From d7a0ecb79a6147157e66c6f4e3dc56cbb0391e6f Mon Sep 17 00:00:00 2001
From: FuelBoard Contributor <fuelboard@localhost>
Date: Sun, 11 Oct 2026 14:34:53 +0100
Subject: [PATCH] Add Worth the Drive fuel savings with road-routed estimates
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Optional Fuel Savings feature (off by default): vehicle MPG in UK imperial gallons, fill amount in pounds or litres, persisted through the existing keychain/app-group store. Ranks the WHOLE station pool by estimated net saving (fuel-price saving at each pump minus the extra return-trip driving cost) using MapKit road distances with a straight-line fallback marked (est.).

The closest station with a valid price for the selected fuel is the comparison baseline and is labelled "Closest station"; other rows read "Save £X.XX after travel" / "£X.XX worse off after travel" / "Break even". Labels live in the shared model so they are unit-tested. The TOP badge still marks the cheapest pump price and reads "CHEAPEST" when the list is ranked by net saving.

Road routing now prioritises the Worth-the-Drive candidates plus the baseline and merges cache entries instead of replacing them, so far-out stations get real routes rather than permanent straight-line estimates. Numeric fields gain a Done button above the keypad (decimalPad has no Return key); the fill-up control is hidden unless the feature is configured; Favourites shares one session fill amount with the station list. 131 tests.
---
 FuelBoard/ContentView.swift                   | 313 +++++++++++++-
 FuelBoard/FavouritesView.swift                |  38 +-
 FuelBoard/FuelSavingsViews.swift              | 140 +++++++
 FuelBoard/KeyboardSupport.swift               |  41 ++
 FuelBoard/RoadDistanceService.swift           |  98 ++++-
 FuelBoard/SettingsView.swift                  |  94 +++++
 FuelBoard/StationDetailView.swift             |  13 +
 FuelBoard/StationsView.swift                  |  45 +-
 .../Sources/FuelBoardShared/FuelSavings.swift |   1 +
 .../FuelSavingsEstimateTests.swift            | 377 +++++++++++++++++
 .../FuelSavingsRoutingTests.swift             |  37 ++
 .../FuelSavingsTests.swift                    |  93 +++++
 .../FuelStoreFileCacheTests.swift             |  69 ++++
 FuelBoardWidgets/FuelPriceWidget.swift        |   5 +-
 Shared/FuelSavings.swift                      | 388 ++++++++++++++++++
 Shared/FuelStore.swift                        | 145 ++++++-
 Shared/MirrorFuelProvider.swift               |  14 +
 17 files changed, 1865 insertions(+), 46 deletions(-)
 create mode 100644 FuelBoard/FuelSavingsViews.swift
 create mode 100644 FuelBoard/KeyboardSupport.swift
 create mode 120000 FuelBoardTests/Sources/FuelBoardShared/FuelSavings.swift
 create mode 100644 FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsEstimateTests.swift
 create mode 100644 FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsRoutingTests.swift
 create mode 100644 FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsTests.swift
 create mode 100644 FuelBoardTests/Tests/FuelBoardSharedTests/FuelStoreFileCacheTests.swift
 create mode 100644 Shared/FuelSavings.swift

diff --git a/FuelBoard/ContentView.swift b/FuelBoard/ContentView.swift
index 4741c88..ef723e7 100644
--- a/FuelBoard/ContentView.swift
+++ b/FuelBoard/ContentView.swift
@@ -22,6 +22,8 @@ struct ContentView: View {
     @State private var distanceUnit: DistanceUnit = FuelStore.loadDistanceUnit()
     @State private var priceDisplayStyle: PriceDisplayStyle = FuelStore.loadPriceDisplayStyle()
     @State private var stationTapAction: StationTapAction = FuelStore.loadStationTapAction()
+    @State private var fuelSavingsSettings: FuelSavingsSettings = FuelStore.loadFuelSavingsSettings()
+    @State private var sessionFuelSavingsAmount: FuelSavingsFillAmount = FuelStore.loadFuelSavingsSettings().preferredAmount
     @State private var favourites: [FavouriteEntry] = FuelStore.loadFavourites()
     @State private var alertsEnabled: Bool = FuelStore.loadAlertsEnabled()
     @State private var alertsRadius: Double = FuelStore.loadAlertsRadius()
@@ -63,15 +65,42 @@ struct ContentView: View {
     private func refreshRoadDistancesIfNeeded() {
         let origin = location ?? FuelStore.loadLocation()
         guard let origin else { return }
+        let priority = worthTheDriveRoutingPriorities(location: origin)
         Task {
             await RoadDistanceService.refreshIfNeeded(
                 stations: stations,
                 lat: origin.lat,
-                lng: origin.lng
+                lng: origin.lng,
+                prioritising: priority
             )
         }
     }
 
+    /// The stations worth spending Apple Maps route requests on: the best
+    /// Worth-the-Drive candidates by estimated net saving, plus the comparison
+    /// baseline (every other row is measured against it).
+    ///
+    /// Ranking is by net saving, so these are typically FURTHER out than the
+    /// nearest stations — the ones nearest-only routing never reached, which is
+    /// why their rows stayed on straight-line estimates.
+    private func worthTheDriveRoutingPriorities(location: Coordinate) -> [FuelStation] {
+        guard fuelSavingsSettings.isConfigured else { return [] }
+        let baseline = nearestSavingsBaseline
+        let ranked = FuelSavingsEstimator.ranked(
+            poolStations,
+            fuel: selectedFuel,
+            baseline: baseline,
+            settings: fuelSavingsSettings,
+            amount: sessionFuelSavingsAmount,
+            journeyMiles: { [self] station in savingsJourneyMiles(for: station, location: location) }
+        )
+        var priorities = Array(ranked.prefix(RoadDistanceService.priorityCandidates))
+        if let baseline, !priorities.contains(where: { $0.id == baseline.id }) {
+            priorities.insert(baseline, at: 0)
+        }
+        return priorities
+    }
+
     private func ensureBackgroundMotionTrackingIfNeeded() {
         if alertsEnabled || liveActivityEnabled {
             locationManager.startBackgroundTracking()
@@ -113,11 +142,11 @@ struct ContentView: View {
     @State private var bannerOffset: CGFloat = 0
     @State private var bannerClearTask: Task<Void, Never>?
 
-    /// The pool the list draws from. In Cheapest mode the chosen miles radius
-    /// bounds it ("best price within X miles"); in Closest mode the radius is
-    /// redundant — the whole country sorted nearest-first, because "nearest"
-    /// must never answer with an empty state. STRICT: no fallback to
-    /// out-of-radius stations in Cheapest mode.
+    /// The pool the list draws from. In Cheapest and Worth-the-Drive modes the
+    /// chosen miles radius bounds it ("best price within X miles"); in Closest
+    /// mode the radius is redundant — the whole country sorted nearest-first,
+    /// because "nearest" must never answer with an empty state. STRICT: no
+    /// fallback to out-of-radius stations in radius-bound modes.
     private var poolStations: [FuelStation] {
         let selling = stations.filter { $0.prices[selectedFuel] != nil }
         guard let location else { return selling }
@@ -180,7 +209,7 @@ struct ContentView: View {
 
     private var sortedStations: [FuelStation] {
         let pool = poolStations
-        switch sortMode {
+        switch effectiveSortMode {
         case .closest:
             guard let location else { return pool.sorted { $0.prices[selectedFuel]! < $1.prices[selectedFuel]! } }
             return pool.sorted { lhs, rhs in
@@ -200,9 +229,165 @@ struct ContentView: View {
                 return lhs.distanceKM(to: location.lat, lng2: location.lng) <
                        rhs.distanceKM(to: location.lat, lng2: location.lng)
             }
+        case .worthTheDrive:
+            return sortedForWorthTheDrive(pool)
         }
     }
 
+    /// Row/detail savings lookup with the comparison baseline resolved ONCE.
+    ///
+    /// `nearestSavingsBaseline` scans the whole station list, and StationsView
+    /// asks for savings once per visible row (plus again for the detail sheet),
+    /// so handing the view a per-station method would rescan ~8k stations
+    /// dozens of times per render.
+    private func savingsLookup(baseline: FuelStation?) -> (FuelStation) -> FuelSavingsAvailability? {
+        guard fuelSavingsSettings.isConfigured else { return { _ in nil } }
+        guard let location else { return { _ in .unavailable("Location unavailable") } }
+        let baselineJourney = baseline.flatMap { savingsJourneyMiles(for: $0, location: location) }
+        return { station in
+            FuelSavingsEstimator.availability(
+                station: station,
+                fuel: selectedFuel,
+                baseline: baseline,
+                settings: fuelSavingsSettings,
+                amount: sessionFuelSavingsAmount,
+                journey: savingsJourneyMiles(for: station, location: location),
+                baselineJourney: baselineJourney
+            )
+        }
+    }
+
+    /// The nearest station that sells the selected fuel — the Worth-the-Drive
+    /// comparison baseline.
+    ///
+    /// Single O(n) pass on purpose: `min(by:)` re-evaluates its closure twice
+    /// per comparison, and each evaluation reads the road-distance cache. With
+    /// the full UK list that is thousands of redundant lookups per render, all
+    /// on the main thread during scene creation (see `loadRoadDistances`).
+    private var nearestSavingsBaseline: FuelStation? {
+        guard let location else { return nil }
+        var bestStation: FuelStation?
+        var bestMiles = Double.infinity
+        for station in stations where station.prices[selectedFuel] != nil {
+            let miles = savingsFallbackMiles(for: station, location: location)
+            if miles < bestMiles {
+                bestMiles = miles
+                bestStation = station
+            }
+        }
+        return bestStation
+    }
+
+    /// The sort the UI and the list actually use.
+    ///
+    /// The Worth-the-Drive sort is only offered while Fuel Savings is
+    /// configured, but the chosen sort is persisted — so a stored
+    /// `.worthTheDrive` would otherwise keep the fill-up control on screen (and
+    /// leave the picker on a mode it no longer lists) after the feature is
+    /// switched off. Fall back to Cheapest for RENDER ONLY: the stored
+    /// preference is left untouched, so re-enabling the feature restores the
+    /// user's choice.
+    private var effectiveSortMode: SortMode {
+        (sortMode == .worthTheDrive && !fuelSavingsSettings.isConfigured) ? .cheapest : sortMode
+    }
+
+    /// Journey (out and back) miles for a station: the measured road route when
+    /// one has been fetched, otherwise a straight-line out-and-back estimate, so
+    /// that every station the app lists can carry a saving.
+    private func savingsJourneyMiles(for station: FuelStation, location: Coordinate) -> FuelSavingsJourney? {
+        if let roadMeters = FuelStore.roadJourneyMeters(for: station, userLat: location.lat, userLng: location.lng) {
+            return FuelSavingsJourney(miles: roadMeters / 1609.34, basis: .roadRoute)
+        }
+        return FuelSavingsJourney(
+            miles: savingsFallbackMiles(for: station, location: location),
+            basis: .straightLine
+        )
+    }
+
+    private func savingsFallbackMiles(for station: FuelStation, location: Coordinate) -> Double {
+        FuelStore.displayDistanceKM(station: station, userLat: location.lat, userLng: location.lng) * 0.621371 * 2
+    }
+
+    private func sortedForWorthTheDrive(_ pool: [FuelStation]) -> [FuelStation] {
+        guard fuelSavingsSettings.isConfigured, let location else {
+            #if DEBUG
+            print("FB-DRIVE skipped configured=\(fuelSavingsSettings.isConfigured) location=\(self.location == nil ? "none" : "ok") pool=\(pool.count)")
+            #endif
+            return pool.sorted { ($0.prices[selectedFuel] ?? .infinity) < ($1.prices[selectedFuel] ?? .infinity) }
+        }
+        // Every station in the pool is ranked, with a straight-line estimate
+        // until its road route has been measured. Ranking only a road-route
+        // shortlist hid cheaper stations a few miles further out and left later
+        // pages with no savings (see `FuelSavingsEstimator.ranked`).
+        let baseline = nearestSavingsBaseline
+        let ordered = FuelSavingsEstimator.ranked(
+            pool,
+            fuel: selectedFuel,
+            baseline: baseline,
+            settings: fuelSavingsSettings,
+            amount: sessionFuelSavingsAmount,
+            journeyMiles: { [self] station in savingsJourneyMiles(for: station, location: location) }
+        )
+        #if DEBUG
+        logWorthTheDriveSummary(ordered, baseline: baseline, location: location)
+        #endif
+        return ordered
+    }
+
+    #if DEBUG
+    /// Last FB-DRIVE line printed, so the ranking (which runs on every render)
+    /// only reports when the result actually changes.
+    private static var lastDriveLogLine: String?
+
+    /// One summary line per ranking pass (FB-DRIVE) so a device console shows
+    /// whether the Worth the Drive list is actually carrying savings for the
+    /// whole pool — the regression was silent otherwise.
+    private func logWorthTheDriveSummary(_ ordered: [FuelStation],
+                                         baseline: FuelStation?,
+                                         location: Coordinate) {
+        let baselineJourney = baseline.flatMap { savingsJourneyMiles(for: $0, location: location) }
+        var rows: [(station: FuelStation, result: FuelSavingsResult, journey: FuelSavingsJourney?)] = []
+        for station in ordered {
+            // Capture the journey ONCE and print that same value: routing runs
+            // in the background, so re-reading it for the log would mix a stale
+            // journey into a fresh figure and make the numbers unreadable.
+            let journey = savingsJourneyMiles(for: station, location: location)
+            guard let availability = FuelSavingsEstimator.availability(
+                station: station,
+                fuel: selectedFuel,
+                baseline: baseline,
+                settings: fuelSavingsSettings,
+                amount: sessionFuelSavingsAmount,
+                journey: journey,
+                baselineJourney: baselineJourney
+            ), let result = availability.result else { continue }
+            rows.append((station, result, journey))
+        }
+        func describe(_ row: (station: FuelStation, result: FuelSavingsResult, journey: FuelSavingsJourney?)) -> String {
+            let price = row.station.prices[selectedFuel].map { String(format: "%.1fp", $0) } ?? "n/a"
+            return "\"\(row.station.name)\" p=\(price) j=\(String(format: "%.1f", row.journey?.miles ?? 0))mi(\(row.journey?.basis.rawValue ?? "none")) gross=\(String(format: "%.2f", row.result.grossSavingGBP)) extra=\(String(format: "%.2f", row.result.extraDrivingCostGBP)) extraMi=\(String(format: "%.1f", row.result.extraDistanceMiles)) net=\(String(format: "%.2f", row.result.netSavingGBP)) \"\(row.result.headline())\""
+        }
+        let baselineLine: String
+        if let baseline, let baselineJourney {
+            let price = baseline.prices[selectedFuel].map { String(format: "%.1fp", $0) } ?? "n/a"
+            baselineLine = "baseline=\"\(baseline.name)\" p=\(price) j=\(String(format: "%.1f", baselineJourney.miles))mi(\(baselineJourney.basis.rawValue))"
+        } else {
+            baselineLine = "baseline=none"
+        }
+        let leaders = rows.prefix(3).map(describe).joined(separator: " | ")
+        let line = "FB-DRIVE pool=\(ordered.count) withSavings=\(rows.count) \(baselineLine) | \(leaders)"
+        guard ContentView.lastDriveLogLine != line else { return }
+        ContentView.lastDriveLogLine = line
+        print(line)
+        // `FB_DRIVE_FOCUS=<text>` prints one named station's row too, so a
+        // specific complaint can be checked against real routed numbers.
+        if let focus = ProcessInfo.processInfo.environment["FB_DRIVE_FOCUS"], !focus.isEmpty,
+           let row = rows.first(where: { $0.station.name.localizedCaseInsensitiveContains(focus) }) {
+            print("FB-DRIVE focus \(describe(row))")
+        }
+    }
+    #endif
+
     /// Station IDs favourited for the CURRENTLY selected fuel — the star on a
     /// Stations-tab row reflects the fuel being viewed (fuel-scoped favourites).
     private var favouriteIDs: Set<String> {
@@ -320,6 +505,26 @@ struct ContentView: View {
                 selectedFuel = f
                 FuelStore.saveSelectedFuel(f)
             }
+            // QA temp: `FB_DRIVE_DEBUG=1` (DEBUG builds only) forces the
+            // optional Fuel Savings feature ON and selects the Worth the Drive
+            // sort, so the ranking can be exercised from the device console
+            // (FB-DRIVE) without tapping through Settings.
+            //
+            // It must NOT substitute the stored MPG / fill amount: doing that
+            // planted the DEFAULT values (45 MPG) over the stored ones and made
+            // every logged figure wrong — the exact opposite of the hook's
+            // purpose. Only `enabled` is overridden; the store is still the
+            // source for MPG and fill.
+            //
+            // An ENVIRONMENT variable, not a launch argument: devicectl clusters
+            // dash-options per character, so a word like `-worthTheDrive` is
+            // parsed as its own `-t` (--timeout) and the launch is rejected.
+            if ProcessInfo.processInfo.environment["FB_DRIVE_DEBUG"] == "1" {
+                var forced = FuelStore.loadFuelSavingsSettings()
+                forced.enabled = true
+                fuelSavingsSettings = forced
+                sortMode = .worthTheDrive
+            }
             // `-forceOfflineDump` / `-forceConnectionProblem` simulate the two
             // failure legs for the screenshot harness. The auto-refresh below
             // is skipped so the banner stays up (a live fetch would clear it).
@@ -335,6 +540,11 @@ struct ContentView: View {
             }
 #else
             showWidgetMock = false
+#endif
+            // Diagnostic only: `effectiveSortMode` already handles a stored
+            // `.worthTheDrive` that the feature can no longer back.
+#if DEBUG
+            print("FB-SAVINGS launch storedSort=\(sortMode.displayName) effective=\(effectiveSortMode.displayName) configured=\(fuelSavingsSettings.isConfigured) enabled=\(fuelSavingsSettings.enabled) mpg=\(fuelSavingsSettings.mpg) amount=\(fuelSavingsSettings.preferredAmount.value)")
 #endif
             // Onboarding runs first on a fresh install — it owns the initial
             // permission prompts (location, notifications, and the data/local
@@ -399,6 +609,13 @@ struct ContentView: View {
                 Task { await refresh(force: true) }
             }
         }
+        .onChange(of: fuelSavingsSettings) { old, new in
+            // Fuel Savings changed in Settings while the app was running: the
+            // effective sort follows automatically (no stored sort is touched).
+#if DEBUG
+            print("FB-SAVINGS settings changed: enabled=\(old.enabled)->\(new.enabled) configured=\(new.isConfigured)")
+#endif
+        }
         .onChange(of: scenePhase) { _, newPhase in
             if newPhase == .active {
                 // Never start location tracking while onboarding is on screen —
@@ -754,12 +971,13 @@ struct ContentView: View {
     /// The Stations tab, extracted from `body` so the TabView expression stays
     /// within the compiler's type-check budget.
     private var stationsTab: some View {
-        StationsView(
+        let baselineStation = nearestSavingsBaseline
+        return StationsView(
             stations: displayedStations,
             totalCount: sortedStations.count,
             isLoading: isLoading,
             selectedFuel: $selectedFuel,
-            sortMode: $sortMode,
+            sortMode: Binding(get: { effectiveSortMode }, set: { sortMode = $0 }),
             stationLimit: $stationLimit,
             distanceUnit: distanceUnit,
             priceDisplayStyle: priceDisplayStyle,
@@ -768,6 +986,10 @@ struct ContentView: View {
             location: location,
             favouriteIDs: favouriteIDs,
             stationTapAction: stationTapAction,
+            fuelSavingsSettings: fuelSavingsSettings,
+            fuelSavingsAmount: $sessionFuelSavingsAmount,
+            savingsForStation: savingsLookup(baseline: baselineStation),
+            savingsBaselineStationName: baselineStation?.name,
             onToggleFavourite: toggleFavourite,
             onRefresh: { await refresh(force: true) }
         )
@@ -776,13 +998,18 @@ struct ContentView: View {
     /// The Favourites tab, extracted from `body` for the same type-check
     /// budget reason.
     private var favouritesTab: some View {
-        FavouritesView(
+        let baselineStation = nearestSavingsBaseline
+        return FavouritesView(
             favourites: refreshedFavourites,
             selectedFuel: selectedFuel,
             location: location,
             distanceUnit: distanceUnit,
             priceDisplayStyle: priceDisplayStyle,
             stationTapAction: stationTapAction,
+            fuelSavingsSettings: fuelSavingsSettings,
+            fuelSavingsAmount: $sessionFuelSavingsAmount,
+            savingsForStation: savingsLookup(baseline: baselineStation),
+            savingsBaselineStationName: baselineStation?.name,
             onToggleFavourite: toggleFavourite,
             onReorder: reorderFavourites,
             onHistoryUnavailable: { if dataStatus == .live { dataStatus = .connectionProblem } },
@@ -822,6 +1049,7 @@ struct ContentView: View {
             distanceUnit: $distanceUnit,
             priceDisplayStyle: $priceDisplayStyle,
             stationTapAction: $stationTapAction,
+            fuelSavingsSettings: $fuelSavingsSettings,
             dataRefreshMode: $dataRefreshMode,
             alertsFuel: alertsFuel,
             alertsRadiusKM: alertsRadius,
@@ -874,12 +1102,56 @@ struct ContentView: View {
         await refresh(force: true)
     }
 
+    /// Shows whatever prices we already have BEFORE the network call settles, so
+    /// a refresh never hides data behind a full-screen spinner. It deliberately
+    /// does NOT touch `dataStatus`: a fetch that is still in flight must not
+    /// flash an offline/connection banner, and a successful fetch clears the
+    /// state anyway. The catch path below labels the state honestly ONLY if the
+    /// fetch really fails.
+    private func showFallbackStationsWhileRefreshing() {
+        guard stations.isEmpty else { return }
+        if let cached = MirrorFuelProvider.cachedStations(
+            near: location?.lat,
+            lng: location?.lng,
+            fuel: selectedFuel,
+            radiusKM: nil
+        ), !cached.isEmpty {
+            stations = cached
+            return
+        }
+        let saved = FuelStore.loadStations()
+        if !saved.isEmpty {
+            stations = saved
+            return
+        }
+        // Bundled snapshot — real but possibly dated. Shown so the list is
+        // never blank while the fetch is in flight; if the fetch fails, the
+        // catch path re-labels it with the honest bundled-dump date.
+        if let dump = BundledDumpProvider.stations, !dump.isEmpty {
+            stations = dump
+        }
+    }
+
     /// Fetches fresh prices, but only when the cache is stale — unless
     /// `force` is true (pull-to-refresh is the manual override).
     private func refresh(force: Bool = false) async {
-        if !force, FuelStore.isCacheFresh {
+        // Freshness ALONE must never skip the fetch: `lastRefresh` is stored
+        // keychain-first (survives reinstall) while the station file lives in
+        // the App Group container (wiped on reinstall). A "fresh" cache with
+        // no cached stations used to short-circuit here and leave the list
+        // empty for ever after every reinstall. Only skip when there is
+        // genuinely something to show.
+        let cachedCount = FuelStore.loadStations().count
+        if !force, FuelStore.isCacheFresh, cachedCount > 0 {
+            #if DEBUG
+            print("FB-REFRESH skip: cache fresh, \(cachedCount) cached stations")
+            #endif
             return  // data already fresh — skip network entirely
         }
+        #if DEBUG
+        print("FB-REFRESH start force=\(force) cached=\(cachedCount)")
+        #endif
+        showFallbackStationsWhileRefreshing()
         isLoading = true
         defer { isLoading = false }
         do {
@@ -890,6 +1162,9 @@ struct ContentView: View {
                 radiusKM: nil  // full-UK dump; device filters by miles radius
             )
             stations = fetched
+            #if DEBUG
+            print("FB-REFRESH ok: \(fetched.count) stations from \(LiveChainProvider.lastSource ?? "?")")
+            #endif
             FuelStore.saveStations(fetched)
             FuelStore.saveLastRefresh()
             if force, FuelStore.hasPendingWatchRefreshRequest {
@@ -918,6 +1193,9 @@ struct ContentView: View {
             // Live data restored — any status banner no longer applies.
             dataStatus = .live
         } catch {
+            #if DEBUG
+            print("FB-REFRESH fail: \(error)")
+            #endif
             if force, FuelStore.hasPendingWatchRefreshRequest {
                 FuelStore.markWatchRefreshHandled()
             }
@@ -959,7 +1237,11 @@ struct StationRow: View {
     let baselinePrice: Double?
     let isTopResult: Bool
     let isFavourite: Bool
+    /// Label for the cheapest-pump-price badge ("TOP" in price/distance order,
+    /// "CHEAPEST" when the list is ranked by net saving).
+    var topBadgeText: String = "TOP"
     var tapAction: StationTapAction = .openMap
+    var fuelSavings: FuelSavingsAvailability?
     var onToggleFavourite: () -> Void = {}
     var onShowDetails: (FuelStation) -> Void = { _ in }
 
@@ -1025,7 +1307,11 @@ struct StationRow: View {
                         .lineLimit(1)
                         .truncationMode(.tail)
                     if isTopResult {
-                        Text("TOP")
+                        // The badge always marks the CHEAPEST PUMP PRICE (never
+                        // "best saving"), so in Worth the Drive order — where
+                        // the top row is the best net saving — it may sit lower
+                        // down the list, and says so.
+                        Text(topBadgeText)
                             .font(.caption2.bold())
                             .padding(.horizontal, 5)
                             .padding(.vertical, 1)
@@ -1050,6 +1336,9 @@ struct StationRow: View {
                         .foregroundStyle(.secondary)
                         .monospacedDigit()
                 }
+                if fuelSavings != nil {
+                    FuelSavingsSummaryView(availability: fuelSavings, amount: .init(value: 0, unit: .pounds), baselineStationName: nil, compact: true)
+                }
             }
             .frame(maxWidth: .infinity, alignment: .leading)
 
diff --git a/FuelBoard/FavouritesView.swift b/FuelBoard/FavouritesView.swift
index 6289da6..b4ae646 100644
--- a/FuelBoard/FavouritesView.swift
+++ b/FuelBoard/FavouritesView.swift
@@ -15,6 +15,16 @@ struct FavouritesView: View {
     let distanceUnit: DistanceUnit
     let priceDisplayStyle: PriceDisplayStyle
     let stationTapAction: StationTapAction
+    /// Fuel Savings config. When it is configured this tab shows the SAME
+    /// fill-up control and per-row estimate as the Stations list: one session
+    /// amount is shared, so adjusting it in either list updates both, and it
+    /// still never touches the Settings default.
+    let fuelSavingsSettings: FuelSavingsSettings
+    @Binding var fuelSavingsAmount: FuelSavingsFillAmount
+    /// Estimated saving for a favourite, against the nearest eligible station —
+    /// the same baseline and definition the Stations list uses.
+    var savingsForStation: (FuelStation) -> FuelSavingsAvailability? = { _ in nil }
+    var savingsBaselineStationName: String?
     var onToggleFavourite: (FuelStation, FuelType) -> Void = { _, _ in }
     /// Persists a reordered favourites array (after drag-and-drop).
     var onReorder: ([FavouriteEntry]) -> Void = { _ in }
@@ -70,6 +80,10 @@ struct FavouritesView: View {
          distanceUnit: DistanceUnit,
          priceDisplayStyle: PriceDisplayStyle,
          stationTapAction: StationTapAction,
+         fuelSavingsSettings: FuelSavingsSettings = .defaults,
+         fuelSavingsAmount: Binding<FuelSavingsFillAmount>,
+         savingsForStation: @escaping (FuelStation) -> FuelSavingsAvailability? = { _ in nil },
+         savingsBaselineStationName: String? = nil,
          onToggleFavourite: @escaping (FuelStation, FuelType) -> Void = { _, _ in },
          onReorder: @escaping ([FavouriteEntry]) -> Void = { _ in },
          onHistoryUnavailable: (() -> Void)? = nil,
@@ -80,6 +94,10 @@ struct FavouritesView: View {
         self.distanceUnit = distanceUnit
         self.priceDisplayStyle = priceDisplayStyle
         self.stationTapAction = stationTapAction
+        self.fuelSavingsSettings = fuelSavingsSettings
+        _fuelSavingsAmount = fuelSavingsAmount
+        self.savingsForStation = savingsForStation
+        self.savingsBaselineStationName = savingsBaselineStationName
         self.onToggleFavourite = onToggleFavourite
         self.onReorder = onReorder
         self.onHistoryUnavailable = onHistoryUnavailable
@@ -124,6 +142,17 @@ struct FavouritesView: View {
                         )
                     }
 
+                    if fuelSavingsSettings.isConfigured {
+                        Section {
+                            FuelSavingsAdjustmentView(
+                                amount: $fuelSavingsAmount,
+                                referencePricePencePerLitre: cheapestPrice
+                            )
+                        } footer: {
+                            Text(String(localized: "Savings below are estimated against the nearest station with a price for this fuel — the same baseline as the Stations list.", comment: "Favourites fuel-savings explanation"))
+                        }
+                    }
+
                     Section {
                         ForEach(Array(ordered.enumerated()), id: \.element.id) { index, station in
                             StationRow(
@@ -133,9 +162,11 @@ struct FavouritesView: View {
                                 distanceUnit: distanceUnit,
                                 priceDisplayStyle: priceDisplayStyle,
                                 baselinePrice: cheapestPrice,
-                                isTopResult: index == 0,
+                                isTopResult: station.id == cheapest?.id,
                                 isFavourite: activeFuelFavouriteIDs.contains(station.id),
+                                topBadgeText: "CHEAPEST",
                                 tapAction: stationTapAction,
+                                fuelSavings: savingsForStation(station),
                                 onToggleFavourite: { onToggleFavourite(station, activeFuel) },
                                 onShowDetails: { detailStation = $0 }
                             )
@@ -183,7 +214,10 @@ struct FavouritesView: View {
                 StationDetailView(
                     station: station,
                     location: location,
-                    distanceUnit: distanceUnit
+                    distanceUnit: distanceUnit,
+                    fuelSavings: savingsForStation(station),
+                    fuelSavingsAmount: fuelSavingsAmount,
+                    savingsBaselineStationName: savingsBaselineStationName
                 )
             }
             .onAppear {
diff --git a/FuelBoard/FuelSavingsViews.swift b/FuelBoard/FuelSavingsViews.swift
new file mode 100644
index 0000000..df0f392
--- /dev/null
+++ b/FuelBoard/FuelSavingsViews.swift
@@ -0,0 +1,140 @@
+import SwiftUI
+
+struct FuelSavingsAdjustmentView: View {
+    @Binding var amount: FuelSavingsFillAmount
+    let referencePricePencePerLitre: Double?
+
+    @State private var textValue: String = ""
+
+    private var range: ClosedRange<Double> {
+        amount.unit == .pounds ? 10...100 : 10...80
+    }
+
+    var body: some View {
+        VStack(alignment: .leading, spacing: 10) {
+            Text("How much are you filling up?")
+                .font(.subheadline.weight(.semibold))
+            Picker("Fill-up unit", selection: unitBinding) {
+                ForEach(FuelSavingsFillUnit.allCases) { unit in
+                    Text(unit.displayName).tag(unit)
+                }
+            }
+            .pickerStyle(.segmented)
+            HStack {
+                Slider(value: sliderBinding, in: range, step: amount.unit == .pounds ? 5 : 1)
+                TextField(amount.unit == .pounds ? "£" : "Litres", text: valueBinding)
+                    .keyboardType(.decimalPad)
+                    .multilineTextAlignment(.trailing)
+                    .frame(width: 72)
+                    .textFieldStyle(.roundedBorder)
+            }
+            Text("Changes the estimate for this session only — your Settings default stays unchanged.")
+                .font(.caption2)
+                .foregroundStyle(.secondary)
+        }
+        .onAppear { syncText() }
+        .onChange(of: amount.value) { _, _ in syncText() }
+        .onChange(of: amount.unit) { _, _ in syncText() }
+    }
+
+    private var unitBinding: Binding<FuelSavingsFillUnit> {
+        Binding(
+            get: { amount.unit },
+            set: { newUnit in
+                guard newUnit != amount.unit else { return }
+                if let referencePricePencePerLitre,
+                   let converted = try? FuelSavingsCalculator.convert(amount: amount, to: newUnit, referencePricePencePerLitre: referencePricePencePerLitre) {
+                    amount = converted
+                } else {
+                    amount = FuelSavingsFillAmount(value: newUnit == .pounds ? 40 : 30, unit: newUnit)
+                }
+                syncText()
+            }
+        )
+    }
+
+    private var sliderBinding: Binding<Double> {
+        Binding(
+            get: { min(max(amount.value, range.lowerBound), range.upperBound) },
+            set: { amount.value = min(max($0, range.lowerBound), range.upperBound) }
+        )
+    }
+
+    private var valueBinding: Binding<String> {
+        Binding(
+            get: { textValue },
+            set: { raw in
+                textValue = raw
+                if let value = Double(raw), value > 0 {
+                    amount.value = min(value, FuelSavingsCalculator.maximumFillAmount(for: amount.unit))
+                }
+            }
+        )
+    }
+
+    private func syncText() {
+        let value = amount.value
+        textValue = value.rounded() == value ? String(format: "%.0f", value) : String(format: "%.1f", value)
+    }
+}
+
+struct FuelSavingsSummaryView: View {
+    let availability: FuelSavingsAvailability?
+    let amount: FuelSavingsFillAmount
+    let baselineStationName: String?
+    var compact: Bool = false
+
+    var body: some View {
+        switch availability {
+        case .available(let result):
+            VStack(alignment: .leading, spacing: compact ? 2 : 8) {
+                Label(result.status.displayName, systemImage: symbol(for: result.status))
+                    .font(compact ? .caption.weight(.semibold) : .headline)
+                Text(result.headline(compact: compact))
+                    .font(compact ? .caption2.bold().monospacedDigit() : .subheadline.bold().monospacedDigit())
+                if !compact {
+                    if result.status == .baseline {
+                        Text("Your closest station with a price for this fuel — every other saving is measured against it.")
+                            .font(.caption)
+                            .foregroundStyle(.secondary)
+                    } else {
+                        Text("Compared with \(baselineStationName ?? "your nearest station") for \(amountText).").font(.caption).foregroundStyle(.secondary)
+                        LabeledContent("Fuel-price saving", value: FuelSavingsFormat.money(result.grossSavingGBP))
+                        LabeledContent("Extra driving cost", value: FuelSavingsFormat.money(result.extraDrivingCostGBP))
+                        LabeledContent("Extra distance", value: String(format: "%.1f miles", result.extraDistanceMiles))
+                        if result.distanceBasis.isEstimate {
+                            Text("Estimated from straight-line distance — refined once the route is measured.")
+                                .font(.caption2)
+                                .foregroundStyle(.secondary)
+                        }
+                        Text("Estimate covers fuel cost only. It excludes time, parking, tolls and wear.")
+                            .font(.caption2)
+                            .foregroundStyle(.secondary)
+                    }
+                }
+            }
+        case .unavailable(let reason):
+            Text(compact ? "Savings unavailable" : "Worth the Drive unavailable: \(reason)")
+                .font(compact ? .caption2 : .caption)
+                .foregroundStyle(.secondary)
+        case nil:
+            EmptyView()
+        }
+    }
+
+    private var amountText: String {
+        switch amount.unit {
+        case .pounds: return String(format: "£%.0f", amount.value)
+        case .litres: return String(format: "%.0f litres", amount.value)
+        }
+    }
+
+    private func symbol(for status: FuelSavingsStatus) -> String {
+        switch status {
+        case .worthTheDrive: return "checkmark.circle.fill"
+        case .breakEven: return "equal.circle.fill"
+        case .notWorthTheDrive: return "xmark.circle.fill"
+        case .baseline: return "location.circle.fill"
+        }
+    }
+}
diff --git a/FuelBoard/KeyboardSupport.swift b/FuelBoard/KeyboardSupport.swift
new file mode 100644
index 0000000..a89f2f5
--- /dev/null
+++ b/FuelBoard/KeyboardSupport.swift
@@ -0,0 +1,41 @@
+import SwiftUI
+import UIKit
+
+extension View {
+    /// Puts a Done button above the keyboard.
+    ///
+    /// The numeric fields (Settings → Average fuel economy and Typical
+    /// fill-up, and the Worth the Drive fill-up box in the station list) use
+    /// `.decimalPad`, which has NO Return key. Without this there is no way to
+    /// dismiss the keyboard once such a field is tapped, and a
+    /// `TextField(value:format:)` only commits the typed value when editing
+    /// ends — so the number never stuck either.
+    ///
+    /// Apply ONCE per screen, to the list or form containing the fields: the
+    /// keyboard toolbar belongs to the focused field, so a single attachment
+    /// covers every field inside it. Attaching it to each field would show
+    /// several Done buttons at once.
+    ///
+    /// - Parameter action: clears the screen's focus state. Prefer this where a
+    ///   `@FocusState` exists; the default resigns the current first responder,
+    ///   which works for fields inside subviews that have no focus binding.
+    func keyboardDoneButton(action: (() -> Void)? = nil) -> some View {
+        toolbar {
+            ToolbarItemGroup(placement: .keyboard) {
+                Spacer()
+                Button("Done") {
+                    if let action {
+                        action()
+                    } else {
+                        UIApplication.shared.sendAction(
+                            #selector(UIResponder.resignFirstResponder),
+                            to: nil,
+                            from: nil,
+                            for: nil
+                        )
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/FuelBoard/RoadDistanceService.swift b/FuelBoard/RoadDistanceService.swift
index b2f8412..246eb6f 100644
--- a/FuelBoard/RoadDistanceService.swift
+++ b/FuelBoard/RoadDistanceService.swift
@@ -16,9 +16,16 @@ import WidgetKit
 
 enum RoadDistanceService {
     /// Upper bound on stations routed per pass, so a pass stays a bounded set of
-    /// route calls. Raised from 12 so stations past the old nearest-12 cutoff
-    /// still get real road distances instead of a straight-line fallback.
-    static let candidatesPerPass = 40
+    /// route calls. Worth-the-Drive now asks for outward AND return routes, so
+    /// this must stay conservative; a larger value can make first launch feel
+    /// unresponsive while MapKit drains dozens of route requests.
+    static let candidatesPerPass = 12
+    /// How many Worth-the-Drive candidates may claim slots in a pass. Those
+    /// rows are ranked by NET SAVING and are typically FURTHER out than the
+    /// nearest stations — routing only the nearest stations (the old behaviour)
+    /// meant they never got a measured route and stayed on straight-line
+    /// estimates forever.
+    static let priorityCandidates = 6
     /// Only route stations within this straight-line radius (km). Covers the
     /// largest search radius the UI exposes (15 mi ≈ 24.1 km) plus margin, so
     /// every station a widget/Live Activity/list can actually show gets routed.
@@ -31,11 +38,34 @@ enum RoadDistanceService {
 
     /// Refreshes the cached road distances for the in-radius stations around
     /// `lat`/`lng`. Throttled by time + distance; safe to call on every fix.
-    static func refreshIfNeeded(stations: [FuelStation], lat: Double, lng: Double) async {
+    ///
+    /// - Parameter priorityStations: stations to route BEFORE the nearest ones
+    ///   (the Worth-the-Drive candidates and the comparison baseline), so the
+    ///   numbers the user actually reads are road-routed rather than estimated.
+    static func refreshIfNeeded(stations: [FuelStation],
+                                lat: Double,
+                                lng: Double,
+                                prioritising priorityStations: [FuelStation] = []) async {
+        guard await refreshGate.begin() else { return }
+        defer { Task { await refreshGate.end() } }
+
         guard !stations.isEmpty else { return }
 
+        let existing = FuelStore.loadRoadDistances()
+        // Entries can only be merged when they were routed from (near enough)
+        // this same origin — the read path rejects anything else anyway.
+        let originCompatible = existing.map {
+            haversineMeters($0.sourceLat, $0.sourceLng, lat, lng) < moveThresholdMeters
+        } ?? false
+
         // Throttle: keep cached values when fresh and the user hasn't moved far.
-        if let cache = FuelStore.loadRoadDistances() {
+        // `FB_ROUTE_REFRESH=1` forces a pass (DEBUG verification hook).
+#if DEBUG
+        let forcePass = ProcessInfo.processInfo.environment["FB_ROUTE_REFRESH"] == "1"
+#else
+        let forcePass = false
+#endif
+        if !forcePass, let cache = existing {
             let elapsed = Date().timeIntervalSince1970 - cache.updatedAt
             let movedMeters = haversineMeters(cache.sourceLat, cache.sourceLng, lat, lng)
             if elapsed < throttleMinutes * 60 && movedMeters < moveThresholdMeters {
@@ -43,33 +73,55 @@ enum RoadDistanceService {
             }
         }
 
-        // Candidate stations: the nearest-by-straight-line subset that the UI
-        // could actually display, capped so a pass stays bounded.
-        let nearest = stations
-            .sorted { $0.distanceKM(to: lat, lng2: lng) < $1.distanceKM(to: lat, lng2: lng) }
-            .prefix(candidatesPerPass)
-            .filter { $0.distanceKM(to: lat, lng2: lng) <= maxRadiusKM }
+        // Candidates: Worth-the-Drive priorities first, then the nearest
+        // stations. Stations that already have a route from this origin are
+        // skipped so the per-pass budget goes on the ones still missing one.
+        var candidates: [FuelStation] = []
+        var seen = Set<String>()
+        func consider(_ station: FuelStation) {
+            guard candidates.count < candidatesPerPass else { return }
+            guard station.distanceKM(to: lat, lng2: lng) <= maxRadiusKM else { return }
+            guard seen.insert(station.id).inserted else { return }
+            guard !FuelStore.hasRoadDistance(for: station, userLat: lat, userLng: lng) else { return }
+            candidates.append(station)
+        }
+        for station in priorityStations.prefix(priorityCandidates) { consider(station) }
+        let nearest = stations.sorted { $0.distanceKM(to: lat, lng2: lng) < $1.distanceKM(to: lat, lng2: lng) }
+        for station in nearest {
+            if candidates.count >= candidatesPerPass { break }
+            consider(station)
+        }
+
+        guard !candidates.isEmpty else { return }
 
         let origin = CLLocationCoordinate2D(latitude: lat, longitude: lng)
-        var entries: [String: CachedRoadDistance] = [:]
-        for station in nearest {
+        var entries: [String: CachedRoadDistance] = originCompatible ? (existing?.entries ?? [:]) : [:]
+        for station in candidates {
             let dest = CLLocationCoordinate2D(latitude: station.lat, longitude: station.lng)
-            if let meters = await roadMeters(from: origin, to: dest) {
+            async let outward = roadMeters(from: origin, to: dest)
+            async let back = roadMeters(from: dest, to: origin)
+            if let meters = await outward {
                 // Store the exact pin that was routed so the display layer can
                 // refuse to serve this value if the station later appears with
                 // a different coordinate (corrected pin / other data source).
+                let returnMeters = await back
                 entries[station.id] = CachedRoadDistance(meters: meters,
                                                          lat: station.lat,
-                                                         lng: station.lng)
+                                                         lng: station.lng,
+                                                         returnMeters: returnMeters)
             }
         }
-        guard !entries.isEmpty else { return }
+        guard entries.count > (originCompatible ? (existing?.entries.count ?? 0) : 0) || !originCompatible else {
+            return
+        }
 
         FuelStore.saveRoadDistances(sourceLat: lat, sourceLng: lng, entries: entries)
         // Wake the widgets so the new road distances surface immediately.
         WidgetCenter.shared.reloadAllTimelines()
     }
 
+    private static let refreshGate = RoadDistanceRefreshGate()
+
     /// Driving distance (metres) between two coordinates via Apple Maps routing.
     private static func roadMeters(from: CLLocationCoordinate2D, to: CLLocationCoordinate2D) async -> Double? {
         let request = MKDirections.Request()
@@ -96,3 +148,17 @@ enum RoadDistanceService {
         return r * 2 * atan2(sqrt(a), sqrt(1 - a))
     }
 }
+
+private actor RoadDistanceRefreshGate {
+    private var isRefreshing = false
+
+    func begin() -> Bool {
+        guard !isRefreshing else { return false }
+        isRefreshing = true
+        return true
+    }
+
+    func end() {
+        isRefreshing = false
+    }
+}
diff --git a/FuelBoard/SettingsView.swift b/FuelBoard/SettingsView.swift
index 5bbf400..e7f010b 100644
--- a/FuelBoard/SettingsView.swift
+++ b/FuelBoard/SettingsView.swift
@@ -19,6 +19,7 @@ struct SettingsView: View {
     @Binding var distanceUnit: DistanceUnit
     @Binding var priceDisplayStyle: PriceDisplayStyle
     @Binding var stationTapAction: StationTapAction
+    @Binding var fuelSavingsSettings: FuelSavingsSettings
     @Binding var dataRefreshMode: DataRefreshMode
     /// The fuel + radius currently configured for alerts (mirrors the Alerts
     /// tab) so the test notification matches what real alerts will say.
@@ -70,6 +71,16 @@ struct SettingsView: View {
     @State private var mediumWidgetDiag: String?
     @State private var installedWidgets: String = ""
 
+    /// Which numeric field in the Fuel Savings section is being edited. Those
+    /// fields use `.decimalPad`, which has no Return key, so the keyboard's
+    /// Done button clears this to dismiss AND commit the typed value.
+    @FocusState private var focusedSavingsField: SavingsField?
+
+    private enum SavingsField: Hashable {
+        case averageMPG
+        case fillAmount
+    }
+
     private func refreshWidgetDiag() {
         smallWidgetDiag = FuelStore.loadWidgetDiag(intentType: "FuelBoardSmallWidget")
         mediumWidgetDiag = FuelStore.loadWidgetDiag(intentType: "FuelBoardWidgetConfigurationIntent")
@@ -137,6 +148,45 @@ struct SettingsView: View {
                     Text("Tapping a station either opens directions straight away or shows its details first.")
                 }
 
+                Section {
+                    Toggle("Enable Worth the Drive", isOn: fuelSavingsEnabledBinding)
+                    HStack {
+                        Text("Average fuel economy")
+                        Spacer()
+                        TextField("45", value: fuelSavingsMPGBinding, format: .number.precision(.fractionLength(0...1)))
+                            .keyboardType(.decimalPad)
+                            .multilineTextAlignment(.trailing)
+                            .frame(width: 80)
+                            .focused($focusedSavingsField, equals: .averageMPG)
+                        Text("MPG")
+                            .foregroundStyle(.secondary)
+                    }
+                    Picker("Fill-up unit", selection: fuelSavingsUnitBinding) {
+                        ForEach(FuelSavingsFillUnit.allCases) { unit in
+                            Text(unit.displayName).tag(unit)
+                        }
+                    }
+                    .pickerStyle(.segmented)
+                    HStack {
+                        Text("Typical fill-up")
+                        Spacer()
+                        TextField("40", value: fuelSavingsAmountBinding, format: .number.precision(.fractionLength(0...1)))
+                            .keyboardType(.decimalPad)
+                            .multilineTextAlignment(.trailing)
+                            .frame(width: 90)
+                            .focused($focusedSavingsField, equals: .fillAmount)
+                    }
+                    if !fuelSavingsSettings.isConfigured && fuelSavingsSettings.enabled {
+                        Text("Enter a realistic UK MPG and fill-up amount before Worth the Drive appears in sorting.")
+                            .font(.caption)
+                            .foregroundStyle(.orange)
+                    }
+                } header: {
+                    Text("Fuel Savings")
+                } footer: {
+                    Text("Worth the Drive estimates fuel cost only, using UK imperial MPG, your typical purchase amount, fuel prices and Apple Maps road distances. Real-world average MPG is better than manufacturer figures; the fill-up amount is your usual purchase, not tank capacity.")
+                }
+
                 Section {
                     Picker("Data checking", selection: $dataRefreshMode) {
                         ForEach(DataRefreshMode.allCases) { mode in
@@ -446,6 +496,9 @@ struct SettingsView: View {
                 }
 
             }
+            // Numeric entry must be escapable: `.decimalPad` has no Return key.
+            .keyboardDoneButton { focusedSavingsField = nil }
+            .scrollDismissesKeyboard(.interactively)
             .navigationTitle("Settings")
             .onAppear {
                 Task { await tipStore.load() }
@@ -565,6 +618,47 @@ struct SettingsView: View {
         return "\(version) (\(build))"
     }
 
+    private var fuelSavingsEnabledBinding: Binding<Bool> {
+        Binding(
+            get: { fuelSavingsSettings.enabled },
+            set: { fuelSavingsSettings.enabled = $0; persistFuelSavingsSettings() }
+        )
+    }
+
+    private var fuelSavingsMPGBinding: Binding<Double> {
+        Binding(
+            get: { fuelSavingsSettings.mpg },
+            set: { fuelSavingsSettings.mpg = min(max($0, 0), FuelSavingsCalculator.maximumMPG); persistFuelSavingsSettings() }
+        )
+    }
+
+    private var fuelSavingsAmountBinding: Binding<Double> {
+        Binding(
+            get: { fuelSavingsSettings.preferredAmount.value },
+            set: {
+                fuelSavingsSettings.preferredAmount.value = min(max($0, 0), FuelSavingsCalculator.maximumFillAmount(for: fuelSavingsSettings.preferredAmount.unit))
+                persistFuelSavingsSettings()
+            }
+        )
+    }
+
+    private var fuelSavingsUnitBinding: Binding<FuelSavingsFillUnit> {
+        Binding(
+            get: { fuelSavingsSettings.preferredAmount.unit },
+            set: { newUnit in
+                fuelSavingsSettings.preferredAmount.unit = newUnit
+                if !fuelSavingsSettings.preferredAmount.isValid {
+                    fuelSavingsSettings.preferredAmount.value = newUnit == .pounds ? 40 : 30
+                }
+                persistFuelSavingsSettings()
+            }
+        )
+    }
+
+    private func persistFuelSavingsSettings() {
+        FuelStore.saveFuelSavingsSettings(fuelSavingsSettings)
+    }
+
     /// "API" when the relay is serving the official Fuel Finder API, "CSV"
     /// when it fell back to the public mirror, "—" when unknown/never fetched.
     private var connectionText: String {
diff --git a/FuelBoard/StationDetailView.swift b/FuelBoard/StationDetailView.swift
index d375273..232766c 100644
--- a/FuelBoard/StationDetailView.swift
+++ b/FuelBoard/StationDetailView.swift
@@ -10,6 +10,9 @@ struct StationDetailView: View {
     let station: FuelStation
     let location: Coordinate?
     let distanceUnit: DistanceUnit
+    var fuelSavings: FuelSavingsAvailability? = nil
+    var fuelSavingsAmount: FuelSavingsFillAmount = FuelSavingsSettings.defaultPreferredAmount
+    var savingsBaselineStationName: String? = nil
     @Environment(\.dismiss) private var dismiss
     @State private var showingReportIssueConfirmation = false
 
@@ -54,6 +57,16 @@ struct StationDetailView: View {
                             .background(Capsule().fill(Color.orange.opacity(0.14)))
                     }
                 }
+                Section {
+                    FuelSavingsSummaryView(
+                        availability: fuelSavings,
+                        amount: fuelSavingsAmount,
+                        baselineStationName: savingsBaselineStationName
+                    )
+                } header: {
+                    Text("Worth the drive?")
+                }
+
                 Section {
                     Button {
                         if let url = station.mapsDirectionsURL {
diff --git a/FuelBoard/StationsView.swift b/FuelBoard/StationsView.swift
index d51bc74..7cebb0b 100644
--- a/FuelBoard/StationsView.swift
+++ b/FuelBoard/StationsView.swift
@@ -16,6 +16,10 @@ struct StationsView: View {
     let location: Coordinate?
     let favouriteIDs: Set<String>
     let stationTapAction: StationTapAction
+    let fuelSavingsSettings: FuelSavingsSettings
+    @Binding var fuelSavingsAmount: FuelSavingsFillAmount
+    var savingsForStation: (FuelStation) -> FuelSavingsAvailability? = { _ in nil }
+    var savingsBaselineStationName: String?
     var onToggleFavourite: (FuelStation, FuelType) -> Void = { _, _ in }
     var onRefresh: () async -> Void = {}
 
@@ -41,7 +45,12 @@ struct StationsView: View {
         let miles = distanceUnit.displayMiles(stationLimit)
         let unit = distanceUnit.label(for: Double(miles))
         let fuel = selectedFuel.displayName
-        let mode = sortMode == .closest ? "Closest" : "Cheapest"
+        let mode: String
+        switch sortMode {
+        case .closest: mode = "Closest"
+        case .cheapest: mode = "Cheapest"
+        case .worthTheDrive: mode = "Worth the Drive"
+        }
         let tapHint = stationTapAction == .openMap
             ? "tap a station for directions."
             : "tap a station for details."
@@ -92,7 +101,7 @@ struct StationsView: View {
 
                 Section("Stations") {
                     Picker("Sort by", selection: $sortMode) {
-                        ForEach(SortMode.allCases) { mode in
+                        ForEach(availableSortModes) { mode in
                             Text(mode.displayName).tag(mode)
                         }
                     }
@@ -102,7 +111,17 @@ struct StationsView: View {
                     }
                     .padding(.vertical, 2)
 
-                    if isLoading {
+                    // Only offered while the feature is actually configured — a
+                    // stale stored sort mode must not keep the control on screen
+                    // for a switched-off feature.
+                    if sortMode == .worthTheDrive && fuelSavingsSettings.isConfigured {
+                        FuelSavingsAdjustmentView(
+                            amount: $fuelSavingsAmount,
+                            referencePricePencePerLitre: baselinePrice
+                        )
+                    }
+
+                    if isLoading && stations.isEmpty {
                         HStack(spacing: 10) {
                             ProgressView()
                             Text("Fetching prices…")
@@ -133,7 +152,9 @@ struct StationsView: View {
                                 baselinePrice: baselinePrice,
                                 isTopResult: station.id == topStationID,
                                 isFavourite: favouriteIDs.contains(station.id),
+                                topBadgeText: sortMode == .worthTheDrive ? "CHEAPEST" : "TOP",
                                 tapAction: stationTapAction,
+                                fuelSavings: savingsForStation(station),
                                 onToggleFavourite: { onToggleFavourite(station, selectedFuel) },
                                 onShowDetails: { detailStation = $0 }
                             )
@@ -180,6 +201,11 @@ struct StationsView: View {
             // large title at rest, scrolls it away and fades the compact
             // inline title in. No custom toolbar needed — the native mechanism
             // only renders text, which is exactly what we want here.
+            // The Worth the Drive fill-up box uses `.decimalPad`, which has no
+            // Return key — give the keyboard a Done button and let a scroll
+            // dismiss it too.
+            .keyboardDoneButton()
+            .scrollDismissesKeyboard(.interactively)
             .navigationTitle("FuelBoard")
             .navigationBarTitleDisplayMode(.large)
             .onAppear {
@@ -273,12 +299,23 @@ struct StationsView: View {
                 StationDetailView(
                     station: station,
                     location: location,
-                    distanceUnit: distanceUnit
+                    distanceUnit: distanceUnit,
+                    fuelSavings: savingsForStation(station),
+                    fuelSavingsAmount: fuelSavingsAmount,
+                    savingsBaselineStationName: savingsBaselineStationName
                 )
             }
         }
     }
 
+    private var availableSortModes: [SortMode] {
+        var modes: [SortMode] = [.closest, .cheapest]
+        if fuelSavingsSettings.isConfigured {
+            modes.append(.worthTheDrive)
+        }
+        return modes
+    }
+
     /// One price-rating card for the Key sheet: accent icon, title + blurb,
     /// and the rating threshold in the accent colour (mirrors the tip cards).
     private func keyCard(icon: String, color: Color, title: String, blurb: String, threshold: String) -> some View {
diff --git a/FuelBoardTests/Sources/FuelBoardShared/FuelSavings.swift b/FuelBoardTests/Sources/FuelBoardShared/FuelSavings.swift
new file mode 120000
index 0000000..02e2ed3
--- /dev/null
+++ b/FuelBoardTests/Sources/FuelBoardShared/FuelSavings.swift
@@ -0,0 +1 @@
+../../../Shared/FuelSavings.swift
\ No newline at end of file
diff --git a/FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsEstimateTests.swift b/FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsEstimateTests.swift
new file mode 100644
index 0000000..0bb3d49
--- /dev/null
+++ b/FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsEstimateTests.swift
@@ -0,0 +1,377 @@
+import XCTest
+#if SWIFT_PACKAGE
+@testable import FuelBoardShared
+#endif
+
+/// Ranking rules for the Worth the Drive sort.
+///
+/// Regression: the sort used to rank only a shortlist of the nearest stations
+/// whose ROAD ROUTES had been measured, and everything else was listed as
+/// unavailable. Cheaper stations a few miles further out — the exact stations
+/// the sort exists to surface — were dropped from the top of the list, and
+/// stations on later pages showed no savings at all.
+final class FuelSavingsEstimateTests: XCTestCase {
+    private let settings = FuelSavingsSettings(
+        enabled: true,
+        mpg: 45,
+        preferredAmount: FuelSavingsFillAmount(value: 40, unit: .pounds)
+    )
+    private let amount = FuelSavingsFillAmount(value: 40, unit: .pounds)
+
+    private func station(_ id: String,
+                         price: Double?,
+                         lat: Double = 51.5,
+                         lng: Double = -0.1) -> FuelStation {
+        FuelStation(
+            id: id,
+            name: id,
+            brand: "X",
+            address: "",
+            postcode: "",
+            lat: lat,
+            lng: lng,
+            prices: price.map { [FuelType.e10: $0] } ?? [:],
+            priceUpdated: nil
+        )
+    }
+
+    /// Straight-line out-and-back estimate, as the app builds it when no road
+    /// route has been measured yet.
+    private func straightLine(_ miles: Double) -> FuelSavingsJourney {
+        FuelSavingsJourney(miles: miles, basis: .straightLine)
+    }
+
+    func testCheaperStationThreePointFiveMilesAwayIsRankedFirstWithASaving() {
+        // Nearest station: 1 mile away at 145.9p. The station the user can see
+        // in the Cheapest tab: 3.5 miles away at 138.9p.
+        let baseline = station("baseline", price: 145.9)
+        let candidate = station("cheaper-3.5", price: 138.9, lat: 51.55)
+        let filler = (0..<14).map { station("filler-\($0)", price: 150 + Double($0)) }
+        let pool = [baseline, candidate] + filler
+
+        let ranked = FuelSavingsEstimator.ranked(
+            pool,
+            fuel: .e10,
+            baseline: baseline,
+            settings: settings,
+            amount: amount,
+            journeyMiles: { s in
+                switch s.id {
+                case "baseline": return self.straightLine(2.0)
+                case "cheaper-3.5": return self.straightLine(7.0)
+                default: return self.straightLine(20.0)
+                }
+            }
+        )
+
+        XCTAssertEqual(ranked.count, pool.count)
+        XCTAssertEqual(ranked.first?.id, "cheaper-3.5",
+                       "a cheaper station 3.5 miles away must rank above the nearest station")
+
+        let result = FuelSavingsEstimator.availability(
+            station: candidate,
+            fuel: .e10,
+            baseline: baseline,
+            settings: settings,
+            amount: amount,
+            journey: straightLine(7.0),
+            baselineJourney: straightLine(2.0)
+        )?.result
+
+        XCTAssertNotNil(result, "the station must show a saving, not an unavailable state")
+        XCTAssertGreaterThan(result?.netSavingGBP ?? -1, 0)
+        XCTAssertEqual(result?.status, .worthTheDrive)
+        XCTAssertEqual(result?.distanceBasis, .straightLine,
+                       "unmeasured routes are reported as straight-line estimates")
+    }
+
+    func testEveryPricedStationInThePoolIsEstimatedNotJustAShortlist() {
+        // 40 stations, but only the first one has a measured road route — the
+        // old implementation capped the whole ranking to 12 shortlisted
+        // stations and returned "Outside route shortlist" for the rest.
+        let baseline = station("baseline", price: 145.9)
+        let pool = [baseline] + (0..<39).map { station("s\($0)", price: 135 + Double($0)) }
+
+        let ranked = FuelSavingsEstimator.ranked(
+            pool,
+            fuel: .e10,
+            baseline: baseline,
+            settings: settings,
+            amount: amount,
+            journeyMiles: { s in
+                s.id == "baseline"
+                    ? FuelSavingsJourney(miles: 2.0, basis: .roadRoute)
+                    : self.straightLine(2.0 + (Double(s.id.dropFirst()) ?? 6))
+            }
+        )
+
+        XCTAssertEqual(ranked.count, pool.count)
+
+        for station in pool where station.id != "baseline" {
+            let availability = FuelSavingsEstimator.availability(
+                station: station,
+                fuel: .e10,
+                baseline: baseline,
+                settings: settings,
+                amount: amount,
+                journey: straightLine(10.0),
+                baselineJourney: FuelSavingsJourney(miles: 2.0, basis: .roadRoute)
+            )
+            XCTAssertNotNil(availability?.result,
+                            "\(station.id) should carry an estimated saving, not an unavailable state")
+        }
+    }
+
+    func testMeasuredRoadRoutesAreReportedAsRoadRouteBasis() {
+        let baseline = station("baseline", price: 145.9)
+        let candidate = station("candidate", price: 138.9)
+
+        let result = FuelSavingsEstimator.availability(
+            station: candidate,
+            fuel: .e10,
+            baseline: baseline,
+            settings: settings,
+            amount: amount,
+            journey: FuelSavingsJourney(miles: 7.0, basis: .roadRoute),
+            baselineJourney: FuelSavingsJourney(miles: 2.0, basis: .roadRoute)
+        )?.result
+
+        XCTAssertEqual(result?.distanceBasis, .roadRoute)
+        XCTAssertFalse(FuelSavingsDistanceBasis.roadRoute.isEstimate)
+    }
+
+    func testMixedBasisIsReportedAsAnEstimate() {
+        let baseline = station("baseline", price: 145.9)
+        let candidate = station("candidate", price: 138.9)
+
+        // Baseline measured, candidate not: the comparison is only as good as
+        // its weakest leg, so it must be labelled an estimate.
+        let result = FuelSavingsEstimator.availability(
+            station: candidate,
+            fuel: .e10,
+            baseline: baseline,
+            settings: settings,
+            amount: amount,
+            journey: straightLine(7.0),
+            baselineJourney: FuelSavingsJourney(miles: 2.0, basis: .roadRoute)
+        )?.result
+
+        XCTAssertEqual(result?.distanceBasis, .straightLine)
+    }
+
+    func testStationWithoutAPriceIsUnavailable() {
+        let baseline = station("baseline", price: 145.9)
+        let noPrice = station("no-price", price: nil)
+
+        let availability = FuelSavingsEstimator.availability(
+            station: noPrice,
+            fuel: .e10,
+            baseline: baseline,
+            settings: settings,
+            amount: amount,
+            journey: straightLine(4.0),
+            baselineJourney: straightLine(2.0)
+        )
+
+        XCTAssertEqual(availability, .unavailable("No price"))
+    }
+
+    func testFeatureOffProducesNoSavingsRow() {
+        let baseline = station("baseline", price: 145.9)
+        let candidate = station("candidate", price: 138.9)
+
+        let availability = FuelSavingsEstimator.availability(
+            station: candidate,
+            fuel: .e10,
+            baseline: baseline,
+            settings: .defaults,
+            amount: amount,
+            journey: straightLine(4.0),
+            baselineJourney: straightLine(2.0)
+        )
+
+        XCTAssertNil(availability)
+    }
+
+    // MARK: - Required wording and baseline labelling
+
+    private var briefSettings: FuelSavingsSettings {
+        FuelSavingsSettings(enabled: true,
+                            mpg: 30,
+                            preferredAmount: FuelSavingsFillAmount(value: 60, unit: .pounds))
+    }
+
+    private var briefAmount: FuelSavingsFillAmount {
+        FuelSavingsFillAmount(value: 60, unit: .pounds)
+    }
+
+    /// The scenario from the brief: 30 MPG, £60 fill, baseline Rontec Shelf
+    /// (171.9p, 0.4 mi), candidate Shell Whetley Hill (167.9p, 3.8 mi).
+    ///
+    /// Whetley Hill is 4p/litre cheaper, yet it is WORSE OFF — and that is
+    /// correct, not a calculation bug: £60 buys 34.90 L at 171.9p, so the
+    /// cheaper pump saves 34.90 × 4p = £1.40, while the extra 6.8 return miles
+    /// burn 6.8/30 × 4.54609 = 1.03 L at 167.9p = £1.73. Net ≈ −£0.33.
+    func testCheaperStationFurtherAwayIsWorseOffAfterTravel() {
+        let baseline = station("rontec-shelf", price: 171.9)
+        let candidate = station("shell-whetley-hill", price: 167.9)
+
+        let availability = FuelSavingsEstimator.availability(
+            station: candidate,
+            fuel: .e10,
+            baseline: baseline,
+            settings: briefSettings,
+            amount: briefAmount,
+            journey: straightLine(7.6),        // 3.8 mi out and back
+            baselineJourney: straightLine(0.8) // 0.4 mi out and back
+        )
+
+        guard let result = availability?.result else {
+            return XCTFail("expected an estimate, got \(String(describing: availability))")
+        }
+        XCTAssertEqual(result.fillLitres, 34.904, accuracy: 0.005,
+                       "the £60 budget buys litres at the BASELINE pump price")
+        XCTAssertEqual(result.grossSavingGBP, 1.396, accuracy: 0.005)
+        XCTAssertEqual(result.extraDistanceMiles, 6.8, accuracy: 0.001,
+                       "only the return-trip DELTA counts — the shared journey is never counted twice")
+        XCTAssertEqual(result.extraDrivingCostGBP, 1.730, accuracy: 0.005)
+        XCTAssertEqual(result.netSavingGBP, -0.334, accuracy: 0.005)
+        XCTAssertEqual(result.status, .notWorthTheDrive)
+        XCTAssertEqual(result.headline(compact: true), "£0.33 worse off after travel (est.)")
+    }
+
+    func testMeasuredRoadRoutesDropTheEstimateMarker() {
+        let baseline = station("baseline", price: 171.9)
+        let candidate = station("candidate", price: 167.9)
+
+        let availability = FuelSavingsEstimator.availability(
+            station: candidate,
+            fuel: .e10,
+            baseline: baseline,
+            settings: briefSettings,
+            amount: briefAmount,
+            journey: FuelSavingsJourney(miles: 7.6, basis: .roadRoute),
+            baselineJourney: FuelSavingsJourney(miles: 0.8, basis: .roadRoute)
+        )
+
+        XCTAssertEqual(availability?.result?.distanceBasis, .roadRoute)
+        XCTAssertEqual(availability?.result?.headline(compact: true), "£0.33 worse off after travel")
+        XCTAssertEqual(availability?.result?.headline(), "£0.33 worse off after travel")
+    }
+
+    func testBaselineRowIsLabelledClosestStation() {
+        let baseline = station("nearest", price: 171.9)
+
+        let availability = FuelSavingsEstimator.availability(
+            station: baseline,
+            fuel: .e10,
+            baseline: baseline,
+            settings: briefSettings,
+            amount: briefAmount,
+            journey: straightLine(0.8),
+            baselineJourney: straightLine(0.8)
+        )
+
+        XCTAssertEqual(availability?.result?.status, .baseline)
+        XCTAssertEqual(availability?.result?.headline(compact: true), "Closest station")
+        XCTAssertEqual(FuelSavingsStatus.baseline.displayName, "Closest station")
+        XCTAssertEqual(availability?.result?.netSavingGBP, 0)
+        XCTAssertEqual(availability?.result?.extraDistanceMiles, 0)
+    }
+
+    func testPositiveResultHeadlineSaysSaveAfterTravel() {
+        // 4p cheaper AND almost the same distance, so the saving survives travel.
+        let baseline = station("baseline", price: 160.0)
+        let candidate = station("candidate", price: 150.0)
+
+        let availability = FuelSavingsEstimator.availability(
+            station: candidate,
+            fuel: .e10,
+            baseline: baseline,
+            settings: briefSettings,
+            amount: briefAmount,
+            journey: straightLine(6.4),
+            baselineJourney: straightLine(6.0)
+        )
+
+        guard let result = availability?.result else {
+            return XCTFail("expected an estimate, got \(String(describing: availability))")
+        }
+        XCTAssertEqual(result.status, .worthTheDrive)
+        // £60 buys 37.5 L at 160p; 10p/litre cheaper saves £3.75; 0.4 extra
+        // return miles cost ~£0.09. Net ≈ £3.66.
+        XCTAssertEqual(result.netSavingGBP, 3.659, accuracy: 0.005)
+        XCTAssertEqual(result.headline(compact: true), "Save £3.66 after travel (est.)")
+    }
+
+    func testNeutralResultHeadlineIsBreakEven() {
+        // 0.1p cheaper over the same distance: inside the break-even tolerance.
+        let baseline = station("baseline", price: 150.0)
+        let candidate = station("candidate", price: 149.9)
+
+        let availability = FuelSavingsEstimator.availability(
+            station: candidate,
+            fuel: .e10,
+            baseline: baseline,
+            settings: briefSettings,
+            amount: briefAmount,
+            journey: straightLine(6.0),
+            baselineJourney: straightLine(6.0)
+        )
+
+        XCTAssertEqual(availability?.result?.status, .breakEven)
+        XCTAssertEqual(availability?.result?.headline(compact: true), "Break even")
+        XCTAssertEqual(availability?.result?.headline(), "Break even")
+    }
+
+    /// The exact strings the brief asks for.
+    func testHeadlineWordingMatchesTheBrief() {
+        XCTAssertEqual(FuelSavingsResult.baselineHeadline, "Closest station")
+        XCTAssertEqual(FuelSavingsResult.breakEvenHeadline, "Break even")
+
+        let saving = FuelSavingsResult(fillLitres: 34.9,
+                                       grossSavingGBP: 1.40,
+                                       extraDrivingCostGBP: 0.88,
+                                       extraDistanceMiles: 3.5,
+                                       netSavingGBP: 0.52,
+                                       status: .worthTheDrive,
+                                       distanceBasis: .roadRoute)
+        XCTAssertEqual(saving.headline(), "Save £0.52 after travel")
+
+        let loss = FuelSavingsResult(fillLitres: 34.9,
+                                     grossSavingGBP: 1.40,
+                                     extraDrivingCostGBP: 1.71,
+                                     extraDistanceMiles: 6.8,
+                                     netSavingGBP: -0.31,
+                                     status: .notWorthTheDrive,
+                                     distanceBasis: .roadRoute)
+        XCTAssertEqual(loss.headline(), "£0.31 worse off after travel")
+    }
+
+    /// The sort must order by NET saving, not pump price: a pricier station can
+    /// win when the cheaper one is far enough away.
+    func testSortingRanksByNetSavingNotPumpPrice() {
+        let baseline = station("baseline", price: 171.9)
+        let cheapButFar = station("cheap-but-far", price: 167.9)
+        let pricierButNear = station("pricier-but-near", price: 169.9)
+
+        let ranked = FuelSavingsEstimator.ranked(
+            [baseline, cheapButFar, pricierButNear],
+            fuel: .e10,
+            baseline: baseline,
+            settings: briefSettings,
+            amount: briefAmount,
+            journeyMiles: { s in
+                switch s.id {
+                case "baseline": return self.straightLine(0.8)
+                case "cheap-but-far": return self.straightLine(7.6)
+                default: return self.straightLine(1.2)
+                }
+            }
+        )
+
+        XCTAssertEqual(ranked.first?.id, "pricier-but-near",
+                       "net saving decides the order, not the pump price")
+        XCTAssertEqual(ranked.last?.id, "cheap-but-far")
+    }
+}
diff --git a/FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsRoutingTests.swift b/FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsRoutingTests.swift
new file mode 100644
index 0000000..9edfeea
--- /dev/null
+++ b/FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsRoutingTests.swift
@@ -0,0 +1,37 @@
+import XCTest
+#if SWIFT_PACKAGE
+@testable import FuelBoardShared
+#endif
+
+final class FuelSavingsRoutingCacheTests: XCTestCase {
+    override func setUp() {
+        super.setUp()
+        FuelStore.saveRoadDistances(sourceLat: 0, sourceLng: 0, entries: [:])
+    }
+
+    private func station(_ id: String, _ lat: Double, _ lng: Double) -> FuelStation {
+        FuelStation(id: id, name: id, brand: "X", address: "", postcode: "", lat: lat, lng: lng, prices: [.e10: 140], priceUpdated: nil)
+    }
+
+    func testJourneyDistanceUsesSeparateOutAndBackRoadRoutes() {
+        let s = station("a", 51.5074, -0.1278)
+        FuelStore.saveRoadDistances(
+            sourceLat: 51.6,
+            sourceLng: -0.1,
+            entries: ["a": CachedRoadDistance(meters: 3_200, lat: 51.5074, lng: -0.1278, returnMeters: 3_700)]
+        )
+
+        XCTAssertEqual(FuelStore.roadJourneyMeters(for: s, userLat: 51.6, userLng: -0.1), 6_900)
+    }
+
+    func testLegacyOneWayCacheDoublesForJourneyDistance() {
+        let s = station("a", 51.5074, -0.1278)
+        FuelStore.saveRoadDistances(
+            sourceLat: 51.6,
+            sourceLng: -0.1,
+            entries: ["a": CachedRoadDistance(meters: 3_200, lat: 51.5074, lng: -0.1278)]
+        )
+
+        XCTAssertEqual(FuelStore.roadJourneyMeters(for: s, userLat: 51.6, userLng: -0.1), 6_400)
+    }
+}
diff --git a/FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsTests.swift b/FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsTests.swift
new file mode 100644
index 0000000..3f8528e
--- /dev/null
+++ b/FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsTests.swift
@@ -0,0 +1,93 @@
+import XCTest
+#if SWIFT_PACKAGE
+@testable import FuelBoardShared
+#endif
+
+final class FuelSavingsCalculatorTests: XCTestCase {
+    func testUKMPGConversionUsesImperialGallons() {
+        XCTAssertEqual(FuelSavingsCalculator.fuelUsedLitres(distanceMiles: 10, mpg: 45), 1.0102, accuracy: 0.0001)
+    }
+
+    func testPoundsBudgetConvertsToLitresUsingBaselinePrice() throws {
+        let amount = FuelSavingsFillAmount(value: 40, unit: .pounds)
+        let litres = try FuelSavingsCalculator.fillLitres(amount: amount, baselinePricePencePerLitre: 160)
+        XCTAssertEqual(litres, 25.0, accuracy: 0.0001)
+    }
+
+    func testLitresAmountPassesThrough() throws {
+        let amount = FuelSavingsFillAmount(value: 35, unit: .litres)
+        let litres = try FuelSavingsCalculator.fillLitres(amount: amount, baselinePricePencePerLitre: 160)
+        XCTAssertEqual(litres, 35, accuracy: 0.0001)
+    }
+
+    func testNetSavingSubtractsAdditionalDrivingFuelCost() throws {
+        let result = try FuelSavingsCalculator.calculate(
+            mpg: 45,
+            amount: FuelSavingsFillAmount(value: 40, unit: .pounds),
+            baselinePricePencePerLitre: 160,
+            candidatePricePencePerLitre: 150,
+            baselineJourneyMiles: 2,
+            candidateJourneyMiles: 8
+        )
+        XCTAssertEqual(result.fillLitres, 25, accuracy: 0.0001)
+        XCTAssertEqual(result.grossSavingGBP, 2.50, accuracy: 0.0001)
+        XCTAssertEqual(result.extraDistanceMiles, 6, accuracy: 0.0001)
+        XCTAssertEqual(result.extraDrivingCostGBP, 0.9092, accuracy: 0.0001)
+        XCTAssertEqual(result.netSavingGBP, 1.5908, accuracy: 0.0001)
+        XCTAssertEqual(result.status, .worthTheDrive)
+    }
+
+    func testNegativeAndBreakEvenOutcomes() throws {
+        let negative = try FuelSavingsCalculator.calculate(
+            mpg: 45,
+            amount: FuelSavingsFillAmount(value: 10, unit: .litres),
+            baselinePricePencePerLitre: 150,
+            candidatePricePencePerLitre: 149,
+            baselineJourneyMiles: 1,
+            candidateJourneyMiles: 20
+        )
+        XCTAssertEqual(negative.status, .notWorthTheDrive)
+        XCTAssertLessThan(negative.netSavingGBP, 0)
+
+        let even = try FuelSavingsCalculator.calculate(
+            mpg: 45,
+            amount: FuelSavingsFillAmount(value: 10, unit: .litres),
+            baselinePricePencePerLitre: 150,
+            candidatePricePencePerLitre: 150,
+            baselineJourneyMiles: 2,
+            candidateJourneyMiles: 2
+        )
+        XCTAssertEqual(even.status, .breakEven)
+    }
+
+    func testInvalidInputsRejected() {
+        XCTAssertThrowsError(try FuelSavingsCalculator.fillLitres(amount: FuelSavingsFillAmount(value: 40, unit: .pounds), baselinePricePencePerLitre: 0))
+        XCTAssertThrowsError(try FuelSavingsCalculator.calculate(mpg: 0, amount: FuelSavingsFillAmount(value: 40, unit: .pounds), baselinePricePencePerLitre: 160, candidatePricePencePerLitre: 150, baselineJourneyMiles: 1, candidateJourneyMiles: 2))
+        XCTAssertThrowsError(try FuelSavingsCalculator.calculate(mpg: 500, amount: FuelSavingsFillAmount(value: 40, unit: .pounds), baselinePricePencePerLitre: 160, candidatePricePencePerLitre: 150, baselineJourneyMiles: 1, candidateJourneyMiles: 2))
+    }
+
+    func testSwitchingPoundsToLitresPreservesPhysicalQuantity() throws {
+        let pounds = FuelSavingsFillAmount(value: 40, unit: .pounds)
+        let litres = try FuelSavingsCalculator.convert(amount: pounds, to: .litres, referencePricePencePerLitre: 160)
+        XCTAssertEqual(litres.unit, .litres)
+        XCTAssertEqual(litres.value, 25, accuracy: 0.0001)
+        let back = try FuelSavingsCalculator.convert(amount: litres, to: .pounds, referencePricePencePerLitre: 160)
+        XCTAssertEqual(back.value, 40, accuracy: 0.0001)
+    }
+
+    func testSortingPlacesUnavailableAfterSavingsAndBreaksTies() {
+        let a = FuelSavingsRankedStation(stationID: "a", result: .available(.init(fillLitres: 25, grossSavingGBP: 2, extraDrivingCostGBP: 1, extraDistanceMiles: 3, netSavingGBP: 1, status: .worthTheDrive)), distanceMiles: 5, pricePencePerLitre: 150)
+        let b = FuelSavingsRankedStation(stationID: "b", result: .available(.init(fillLitres: 25, grossSavingGBP: 3, extraDrivingCostGBP: 1, extraDistanceMiles: 2, netSavingGBP: 2, status: .worthTheDrive)), distanceMiles: 8, pricePencePerLitre: 149)
+        let c = FuelSavingsRankedStation(stationID: "c", result: .unavailable("No route"), distanceMiles: 1, pricePencePerLitre: 140)
+        XCTAssertEqual(FuelSavingsCalculator.sortedForWorthTheDrive([a, c, b]).map(\.stationID), ["b", "a", "c"])
+    }
+}
+
+final class FuelSavingsSettingsTests: XCTestCase {
+    func testSettingsValidationRequiresEnabledMPGAndFillAmount() {
+        XCTAssertFalse(FuelSavingsSettings(enabled: false, mpg: 45, preferredAmount: .init(value: 40, unit: .pounds)).isConfigured)
+        XCTAssertFalse(FuelSavingsSettings(enabled: true, mpg: 0, preferredAmount: .init(value: 40, unit: .pounds)).isConfigured)
+        XCTAssertFalse(FuelSavingsSettings(enabled: true, mpg: 45, preferredAmount: .init(value: 0, unit: .pounds)).isConfigured)
+        XCTAssertTrue(FuelSavingsSettings(enabled: true, mpg: 45, preferredAmount: .init(value: 40, unit: .pounds)).isConfigured)
+    }
+}
diff --git a/FuelBoardTests/Tests/FuelBoardSharedTests/FuelStoreFileCacheTests.swift b/FuelBoardTests/Tests/FuelBoardSharedTests/FuelStoreFileCacheTests.swift
new file mode 100644
index 0000000..e3f2f77
--- /dev/null
+++ b/FuelBoardTests/Tests/FuelBoardSharedTests/FuelStoreFileCacheTests.swift
@@ -0,0 +1,69 @@
+import XCTest
+@testable import FuelBoardShared
+
+/// Shared payload storage must survive an install whose provisioning profile
+/// has NO `com.apple.security.application-groups` entitlement (free/personal
+/// team and SideStore installs) — the exact situation this test runner is in.
+///
+/// Regression guard: `appGroupFileURL` used to return nil without a group
+/// container, so every save silently failed and every load returned empty. That
+/// left `loadStations()` permanently empty (letting the freshness gate skip the
+/// fetch for ever, i.e. a blank station list) and re-downloaded the ~2.8 MB
+/// dump on every refresh. Storage now falls back to the app's own container.
+final class FuelStoreFileCacheTests: XCTestCase {
+
+    func testSharedFileURLExistsWithoutAppGroupContainer() {
+        XCTAssertNotNil(
+            FuelStore.appGroupFileURL("fuelboard.test.probe.json"),
+            "storage must resolve to a writable location even when the App Group container is unprovisioned"
+        )
+    }
+
+    func testSharedFileRoundTripsWithoutAppGroupContainer() throws {
+        let name = "fuelboard.test.roundtrip.json"
+        let payload = Data("hello-cache".utf8)
+
+        XCTAssertTrue(
+            FuelStore.saveAppGroupFile(payload, name: name),
+            "save must succeed without an App Group container"
+        )
+        XCTAssertEqual(FuelStore.loadAppGroupFile(name), payload)
+
+        if let url = FuelStore.appGroupFileURL(name) {
+            try? FileManager.default.removeItem(at: url)
+        }
+    }
+
+    /// The dump cache is what stops a ~2.8 MB re-download on every refresh, so
+    /// it must round-trip too — not just the station list.
+    func testDumpCacheRoundTripsWithoutAppGroupContainer() {
+        let day = "2026-01-01"
+        let data = Data(repeating: 7, count: 4096)
+
+        MirrorFuelProvider.saveDumpCache(day: day, data: data)
+        let cache = MirrorFuelProvider.loadDumpCache()
+
+        XCTAssertEqual(cache?.day, day, "cached dump day must survive a round-trip")
+        XCTAssertEqual(cache?.data, data, "cached dump payload must survive a round-trip")
+
+        if let url = FuelStore.appGroupFileURL(MirrorFuelProvider.liveDumpCacheFileName) {
+            try? FileManager.default.removeItem(at: url)
+        }
+    }
+
+    /// The road-distance cache is memoized in memory because re-reading it per
+    /// station (it lives in the keychain) stalled the main thread past the iOS
+    /// launch watchdog. A save must therefore invalidate the memo — a stale
+    /// in-memory cache would show wrong distances after a route refresh.
+    func testRoadDistanceMemoRefreshesAfterSave() {
+        FuelStore.saveRoadDistances(sourceLat: 51.0, sourceLng: -1.0, entries: [:])
+        XCTAssertEqual(FuelStore.loadRoadDistances()?.sourceLat, 51.0)
+
+        FuelStore.saveRoadDistances(sourceLat: 52.0, sourceLng: -2.0, entries: [:])
+
+        XCTAssertEqual(
+            FuelStore.loadRoadDistances()?.sourceLat, 52.0,
+            "load must reflect the newest save, not a stale memoized cache"
+        )
+    }
+}
diff --git a/FuelBoardWidgets/FuelPriceWidget.swift b/FuelBoardWidgets/FuelPriceWidget.swift
index eee9e23..8f12de6 100644
--- a/FuelBoardWidgets/FuelPriceWidget.swift
+++ b/FuelBoardWidgets/FuelPriceWidget.swift
@@ -242,8 +242,9 @@ struct FuelPriceTimelineProvider<Configuration: WidgetConfigurationIntent & Widg
                     }
                     return lhs.prices[fuel]! < rhs.prices[fuel]!
                 }
-            case .cheapest:
-                // Cheapest first; distance only breaks ties.
+            case .cheapest, .worthTheDrive:
+                // Cheapest first; distance only breaks ties. Worth-the-Drive is app-only;
+                // widgets fall back to cheapest ordering if a stored config ever carries it.
                 ordered = filtered.sorted { lhs, rhs in
                     let lPrice = lhs.prices[fuel]!
                     let rPrice = rhs.prices[fuel]!
diff --git a/Shared/FuelSavings.swift b/Shared/FuelSavings.swift
new file mode 100644
index 0000000..3f54fd0
--- /dev/null
+++ b/Shared/FuelSavings.swift
@@ -0,0 +1,388 @@
+import Foundation
+
+enum FuelSavingsFillUnit: String, Codable, CaseIterable, Identifiable {
+    case pounds
+    case litres
+
+    var id: String { rawValue }
+
+    var displayName: String {
+        switch self {
+        case .pounds: return "£"
+        case .litres: return "Litres"
+        }
+    }
+}
+
+struct FuelSavingsFillAmount: Codable, Equatable {
+    var value: Double
+    var unit: FuelSavingsFillUnit
+
+    var isValid: Bool {
+        value.isFinite && value > 0 && value <= FuelSavingsCalculator.maximumFillAmount(for: unit)
+    }
+}
+
+struct FuelSavingsSettings: Codable, Equatable {
+    var enabled: Bool
+    var mpg: Double
+    var preferredAmount: FuelSavingsFillAmount
+
+    static let defaultMPG: Double = 45
+    static let defaultPreferredAmount = FuelSavingsFillAmount(value: 40, unit: .pounds)
+
+    static var defaults: FuelSavingsSettings {
+        FuelSavingsSettings(enabled: false, mpg: defaultMPG, preferredAmount: defaultPreferredAmount)
+    }
+
+    var isConfigured: Bool {
+        enabled && FuelSavingsCalculator.isValidMPG(mpg) && preferredAmount.isValid
+    }
+}
+
+enum FuelSavingsStatus: String, Codable, Equatable {
+    case worthTheDrive
+    case breakEven
+    case notWorthTheDrive
+    /// The comparison baseline itself — the station every other saving is
+    /// measured against. Shown as "Closest station", never "Break even".
+    case baseline
+
+    var displayName: String {
+        switch self {
+        case .worthTheDrive: return "Worth the drive"
+        case .breakEven: return "Break even"
+        case .notWorthTheDrive: return "Not worth the drive"
+        case .baseline: return FuelSavingsResult.baselineHeadline
+        }
+    }
+}
+
+/// How the journey distances behind an estimate were obtained.
+enum FuelSavingsDistanceBasis: String, Codable, Equatable {
+    /// Measured road route, out and back, from the routing service.
+    case roadRoute
+    /// Straight-line out-and-back estimate, used until a route is measured.
+    case straightLine
+
+    var isEstimate: Bool { self == .straightLine }
+}
+
+struct FuelSavingsResult: Codable, Equatable {
+    let fillLitres: Double
+    let grossSavingGBP: Double
+    let extraDrivingCostGBP: Double
+    let extraDistanceMiles: Double
+    let netSavingGBP: Double
+    let status: FuelSavingsStatus
+    let distanceBasis: FuelSavingsDistanceBasis
+
+    init(fillLitres: Double,
+         grossSavingGBP: Double,
+         extraDrivingCostGBP: Double,
+         extraDistanceMiles: Double,
+         netSavingGBP: Double,
+         status: FuelSavingsStatus,
+         distanceBasis: FuelSavingsDistanceBasis = .roadRoute) {
+        self.fillLitres = fillLitres
+        self.grossSavingGBP = grossSavingGBP
+        self.extraDrivingCostGBP = extraDrivingCostGBP
+        self.extraDistanceMiles = extraDistanceMiles
+        self.netSavingGBP = netSavingGBP
+        self.status = status
+        self.distanceBasis = distanceBasis
+    }
+}
+
+/// Money formatting for savings strings, in one place so the exact wording the
+/// UI shows is testable.
+enum FuelSavingsFormat {
+    static func money(_ value: Double) -> String {
+        String(format: "£%.2f", value)
+    }
+}
+
+extension FuelSavingsResult {
+    /// Baseline row label — required wording.
+    static let baselineHeadline = "Closest station"
+    /// Neutral result label — required wording.
+    static let breakEvenHeadline = "Break even"
+
+    /// The same estimate relabelled as the comparison baseline: nothing to save
+    /// or lose against itself, and no extra travel.
+    func asBaseline() -> FuelSavingsResult {
+        FuelSavingsResult(
+            fillLitres: fillLitres,
+            grossSavingGBP: 0,
+            extraDrivingCostGBP: 0,
+            extraDistanceMiles: 0,
+            netSavingGBP: 0,
+            status: .baseline,
+            distanceBasis: distanceBasis
+        )
+    }
+
+    /// Row headline, e.g. "Save £0.52 after travel", "£0.31 worse off after
+    /// travel", "Break even", "Closest station".
+    ///
+    /// `compact` (list rows) also marks a straight-line estimate with "(est.)";
+    /// the detail view spells that out in full instead.
+    func headline(compact: Bool = false) -> String {
+        let estimate = (compact && distanceBasis.isEstimate) ? " (est.)" : ""
+        switch status {
+        case .baseline:
+            return Self.baselineHeadline
+        case .breakEven:
+            return Self.breakEvenHeadline
+        case .worthTheDrive:
+            return "Save \(FuelSavingsFormat.money(netSavingGBP)) after travel\(estimate)"
+        case .notWorthTheDrive:
+            return "\(FuelSavingsFormat.money(abs(netSavingGBP))) worse off after travel\(estimate)"
+        }
+    }
+}
+
+/// One station's journey distance, plus how it was obtained.
+struct FuelSavingsJourney: Equatable {
+    let miles: Double
+    let basis: FuelSavingsDistanceBasis
+}
+
+enum FuelSavingsAvailability: Equatable {
+    case available(FuelSavingsResult)
+    case unavailable(String)
+
+    var result: FuelSavingsResult? {
+        if case .available(let result) = self { return result }
+        return nil
+    }
+}
+
+struct FuelSavingsRankedStation: Equatable {
+    let stationID: String
+    let result: FuelSavingsAvailability
+    let distanceMiles: Double
+    let pricePencePerLitre: Double
+}
+
+enum FuelSavingsError: Error, Equatable {
+    case invalidMPG
+    case invalidAmount
+    case invalidPrice
+    case invalidDistance
+}
+
+enum FuelSavingsCalculator {
+    static let imperialGallonLitres = 4.54609
+    static let breakEvenToleranceGBP = 0.05
+    static let minimumMPG: Double = 5
+    static let maximumMPG: Double = 200
+
+    static func maximumFillAmount(for unit: FuelSavingsFillUnit) -> Double {
+        switch unit {
+        case .pounds: return 500
+        case .litres: return 250
+        }
+    }
+
+    static func isValidMPG(_ mpg: Double) -> Bool {
+        mpg.isFinite && mpg >= minimumMPG && mpg <= maximumMPG
+    }
+
+    static func fuelUsedLitres(distanceMiles: Double, mpg: Double) -> Double {
+        distanceMiles / mpg * imperialGallonLitres
+    }
+
+    static func fillLitres(amount: FuelSavingsFillAmount, baselinePricePencePerLitre: Double) throws -> Double {
+        guard amount.isValid else { throw FuelSavingsError.invalidAmount }
+        switch amount.unit {
+        case .litres:
+            return amount.value
+        case .pounds:
+            guard baselinePricePencePerLitre.isFinite, baselinePricePencePerLitre > 0 else {
+                throw FuelSavingsError.invalidPrice
+            }
+            return amount.value / (baselinePricePencePerLitre / 100.0)
+        }
+    }
+
+    static func convert(amount: FuelSavingsFillAmount,
+                        to unit: FuelSavingsFillUnit,
+                        referencePricePencePerLitre: Double) throws -> FuelSavingsFillAmount {
+        guard referencePricePencePerLitre.isFinite, referencePricePencePerLitre > 0 else {
+            throw FuelSavingsError.invalidPrice
+        }
+        guard amount.isValid else { throw FuelSavingsError.invalidAmount }
+        guard amount.unit != unit else { return amount }
+        switch (amount.unit, unit) {
+        case (.pounds, .litres):
+            return FuelSavingsFillAmount(
+                value: amount.value / (referencePricePencePerLitre / 100.0),
+                unit: .litres
+            )
+        case (.litres, .pounds):
+            return FuelSavingsFillAmount(
+                value: amount.value * (referencePricePencePerLitre / 100.0),
+                unit: .pounds
+            )
+        case (.pounds, .pounds), (.litres, .litres):
+            return amount
+        }
+    }
+
+    static func calculate(mpg: Double,
+                          amount: FuelSavingsFillAmount,
+                          baselinePricePencePerLitre: Double,
+                          candidatePricePencePerLitre: Double,
+                          baselineJourneyMiles: Double,
+                          candidateJourneyMiles: Double,
+                          distanceBasis: FuelSavingsDistanceBasis = .roadRoute,
+                          breakEvenToleranceGBP: Double = Self.breakEvenToleranceGBP) throws -> FuelSavingsResult {
+        guard isValidMPG(mpg) else { throw FuelSavingsError.invalidMPG }
+        guard baselinePricePencePerLitre.isFinite, baselinePricePencePerLitre > 0,
+              candidatePricePencePerLitre.isFinite, candidatePricePencePerLitre > 0 else {
+            throw FuelSavingsError.invalidPrice
+        }
+        guard baselineJourneyMiles.isFinite, candidateJourneyMiles.isFinite,
+              baselineJourneyMiles >= 0, candidateJourneyMiles >= 0 else {
+            throw FuelSavingsError.invalidDistance
+        }
+        let fillLitres = try fillLitres(amount: amount, baselinePricePencePerLitre: baselinePricePencePerLitre)
+        let baselinePriceGBP = baselinePricePencePerLitre / 100.0
+        let candidatePriceGBP = candidatePricePencePerLitre / 100.0
+        let grossSaving = fillLitres * (baselinePriceGBP - candidatePriceGBP)
+        let extraDistance = max(0, candidateJourneyMiles - baselineJourneyMiles)
+        let extraFuelLitres = fuelUsedLitres(distanceMiles: extraDistance, mpg: mpg)
+        let extraFuelCost = extraFuelLitres * candidatePriceGBP
+        let netSaving = grossSaving - extraFuelCost
+        let status: FuelSavingsStatus
+        if netSaving > breakEvenToleranceGBP {
+            status = .worthTheDrive
+        } else if netSaving < -breakEvenToleranceGBP {
+            status = .notWorthTheDrive
+        } else {
+            status = .breakEven
+        }
+        return FuelSavingsResult(
+            fillLitres: fillLitres,
+            grossSavingGBP: grossSaving,
+            extraDrivingCostGBP: extraFuelCost,
+            extraDistanceMiles: extraDistance,
+            netSavingGBP: netSaving,
+            status: status,
+            distanceBasis: distanceBasis
+        )
+    }
+
+    static func sortedForWorthTheDrive(_ stations: [FuelSavingsRankedStation]) -> [FuelSavingsRankedStation] {
+        stations.sorted { lhs, rhs in
+            switch (lhs.result.result, rhs.result.result) {
+            case let (l?, r?):
+                if l.netSavingGBP != r.netSavingGBP { return l.netSavingGBP > r.netSavingGBP }
+                if lhs.distanceMiles != rhs.distanceMiles { return lhs.distanceMiles < rhs.distanceMiles }
+                if lhs.pricePencePerLitre != rhs.pricePencePerLitre { return lhs.pricePencePerLitre < rhs.pricePencePerLitre }
+                return lhs.stationID < rhs.stationID
+            case (_?, nil):
+                return true
+            case (nil, _?):
+                return false
+            case (nil, nil):
+                if lhs.distanceMiles != rhs.distanceMiles { return lhs.distanceMiles < rhs.distanceMiles }
+                return lhs.stationID < rhs.stationID
+            }
+        }
+    }
+}
+
+/// Turns stations into savings estimates.
+///
+/// Pure and injectable (no MapKit, CoreLocation or SwiftUI) so the ranking
+/// rules are unit tested directly.
+enum FuelSavingsEstimator {
+    /// Savings for a single station against `baseline`, or nil when there is
+    /// nothing to show at all (feature off).
+    static func availability(station: FuelStation,
+                             fuel: FuelType,
+                             baseline: FuelStation?,
+                             settings: FuelSavingsSettings,
+                             amount: FuelSavingsFillAmount,
+                             journey: FuelSavingsJourney?,
+                             baselineJourney: FuelSavingsJourney?) -> FuelSavingsAvailability? {
+        guard settings.isConfigured else { return nil }
+        guard let baseline, let baselineJourney else { return .unavailable("No comparison station") }
+        guard let baselinePrice = baseline.prices[fuel] else { return .unavailable("No comparison station") }
+        guard let price = station.prices[fuel] else { return .unavailable("No price") }
+        guard let journey else { return .unavailable("Distance unavailable") }
+        // Both legs must be measured for the estimate to count as a road-route
+        // one; otherwise it is reported as a straight-line estimate.
+        let basis: FuelSavingsDistanceBasis =
+            (journey.basis == .roadRoute && baselineJourney.basis == .roadRoute) ? .roadRoute : .straightLine
+        do {
+            let result = try FuelSavingsCalculator.calculate(
+                mpg: settings.mpg,
+                amount: amount,
+                baselinePricePencePerLitre: baselinePrice,
+                candidatePricePencePerLitre: price,
+                baselineJourneyMiles: baselineJourney.miles,
+                candidateJourneyMiles: journey.miles,
+                distanceBasis: basis
+            )
+            // The baseline compares against itself: label it as the closest
+            // station rather than a meaningless "Break even".
+            return .available(station.id == baseline.id ? result.asBaseline() : result)
+        } catch {
+            return .unavailable("Distance unavailable")
+        }
+    }
+
+    /// Ranks a whole pool for the Worth the Drive sort.
+    ///
+    /// EVERY priced station in the pool gets an estimate, not just the handful
+    /// whose road routes happen to have been measured: journeys that have no
+    /// measured route fall back to a straight-line out-and-back estimate (see
+    /// `FuelSavingsDistanceBasis`). Capping this to a shortlist dropped cheaper
+    /// stations that were a few miles further away — the exact stations the
+    /// sort exists to surface — and left later pages with no savings at all.
+    static func ranked(_ stations: [FuelStation],
+                       fuel: FuelType,
+                       baseline: FuelStation?,
+                       settings: FuelSavingsSettings,
+                       amount: FuelSavingsFillAmount,
+                       journeyMiles: (FuelStation) -> FuelSavingsJourney?) -> [FuelStation] {
+        var journeys: [String: FuelSavingsJourney] = [:]
+        journeys.reserveCapacity(stations.count)
+        for station in stations {
+            if let journey = journeyMiles(station) {
+                journeys[station.id] = journey
+            }
+        }
+        let baselineJourney = baseline.flatMap { journeys[$0.id] }
+        let ranked = stations.map { station -> FuelSavingsRankedStation in
+            let journey = journeys[station.id]
+            let availability = availability(station: station,
+                                            fuel: fuel,
+                                            baseline: baseline,
+                                            settings: settings,
+                                            amount: amount,
+                                            journey: journey,
+                                            baselineJourney: baselineJourney) ?? .unavailable("Unavailable")
+            return FuelSavingsRankedStation(
+                stationID: station.id,
+                result: availability,
+                distanceMiles: journey?.miles ?? .greatestFiniteMagnitude,
+                pricePencePerLitre: station.prices[fuel] ?? .infinity
+            )
+        }
+        let order = Dictionary(
+            uniqueKeysWithValues: FuelSavingsCalculator.sortedForWorthTheDrive(ranked)
+                .enumerated()
+                .map { ($0.element.stationID, $0.offset) }
+        )
+        return stations.sorted { lhs, rhs in
+            let left = order[lhs.id] ?? Int.max
+            let right = order[rhs.id] ?? Int.max
+            if left != right { return left < right }
+            return lhs.id < rhs.id
+        }
+    }
+}
diff --git a/Shared/FuelStore.swift b/Shared/FuelStore.swift
index f0ed5bd..6fa6875 100644
--- a/Shared/FuelStore.swift
+++ b/Shared/FuelStore.swift
@@ -45,6 +45,7 @@ struct FavouriteAlertSnapshot: Codable, Equatable {
 enum SortMode: String, Codable, CaseIterable, Identifiable {
     case cheapest
     case closest
+    case worthTheDrive
 
     var id: String { rawValue }
 
@@ -52,6 +53,7 @@ enum SortMode: String, Codable, CaseIterable, Identifiable {
         switch self {
         case .cheapest: return "Cheapest"
         case .closest: return "Closest"
+        case .worthTheDrive: return "Worth the Drive"
         }
     }
 }
@@ -419,15 +421,47 @@ struct FuelStore {
     static let relaySourceKey = "fuelboard.relaySource"      // String — "api" | "csv"
     static let stationCountKey = "fuelboard.stationCount"    // String — station count
     static let dataUpdatedKey = "fuelboard.dataUpdated"      // govUK dataset update time
+    static let fuelSavingsEnabledKey = "fuelboard.fuelSavings.enabled"
+    static let fuelSavingsMPGKey = "fuelboard.fuelSavings.mpg"
+    static let fuelSavingsAmountKey = "fuelboard.fuelSavings.amount"
+    static let fuelSavingsUnitKey = "fuelboard.fuelSavings.unit"
 
     // Large shared payloads belong in the App Group container, not
     // UserDefaults/CFPreferences (which has a roughly 4 MB limit).
     static let stationsFileName = "fuelboard.stations.json"
 
+    /// Where a shared payload is written: the App Group container when the
+    /// provisioning profile grants it, otherwise the app's OWN container.
+    ///
+    /// This fallback is essential in the field. Free/personal-team and SideStore
+    /// profiles do NOT include the `com.apple.security.application-groups`
+    /// entitlement, so `containerURL(forSecurityApplicationGroupIdentifier:)`
+    /// returns nil at runtime. Without this fallback NOTHING persisted on those
+    /// installs: `loadStations()` was permanently empty (so the freshness gate
+    /// could skip the fetch for ever and leave a blank list) and the ~2.8 MB
+    /// dump was re-downloaded on every refresh. The app's own container is not
+    /// shared with the widget/watch extension, but the app itself must keep a
+    /// working cache.
     static func appGroupFileURL(_ name: String) -> URL? {
-        FileManager.default
-            .containerURL(forSecurityApplicationGroupIdentifier: appGroupSuite)?
-            .appendingPathComponent(name, isDirectory: false)
+        let fm = FileManager.default
+        if let group = fm.containerURL(forSecurityApplicationGroupIdentifier: appGroupSuite),
+           fm.fileExists(atPath: group.path) {
+            // Only use the App Group container when the system actually
+            // provisioned it at install time (i.e. the profile carries the
+            // `com.apple.security.application-groups` entitlement). Never try to
+            // create it: when the entitlement is missing the path either does
+            // not exist or is not writable, and probing it that way failed every
+            // write instead of falling back.
+            return group.appendingPathComponent(name, isDirectory: false)
+        }
+        guard let dir = fm.urls(for: .applicationSupportDirectory, in: .userDomainMask).first else {
+            return nil
+        }
+        if !fm.fileExists(atPath: dir.path),
+           (try? fm.createDirectory(at: dir, withIntermediateDirectories: true)) == nil {
+            return nil
+        }
+        return dir.appendingPathComponent(name, isDirectory: false)
     }
 
     static func loadAppGroupFile(_ name: String) -> Data? {
@@ -467,6 +501,10 @@ struct FuelStore {
     }
 
     static func loadStations() -> [FuelStation] {
+        #if DEBUG
+        let probe = appGroupFileURL(stationsFileName)
+        print("FB-STORAGE load \(stationsFileName) url=\(probe?.path ?? "nil") present=\(probe.map { FileManager.default.fileExists(atPath: $0.path) } ?? false)")
+        #endif
         if let data = loadAppGroupFile(stationsFileName),
            let stations = try? JSONDecoder().decode([FuelStation].self, from: data),
            !stations.isEmpty {
@@ -500,7 +538,10 @@ struct FuelStore {
 
     static func saveStations(_ stations: [FuelStation]) {
         if let data = try? JSONEncoder().encode(stations) {
-            _ = saveAppGroupFile(data, name: stationsFileName)
+            let ok = saveAppGroupFile(data, name: stationsFileName)
+            #if DEBUG
+            print("FB-STORAGE save \(stationsFileName) bytes=\(data.count) ok=\(ok) url=\(appGroupFileURL(stationsFileName)?.path ?? "nil")")
+            #endif
         }
     }
 
@@ -632,6 +673,41 @@ struct FuelStore {
         saveString(action.rawValue, service: stationTapActionKey)
     }
 
+    // MARK: Fuel savings — Worth the Drive?
+
+    static func loadFuelSavingsSettings() -> FuelSavingsSettings {
+        let enabled = loadString(service: fuelSavingsEnabledKey) == "1"
+        let mpg = loadString(service: fuelSavingsMPGKey).flatMap(Double.init) ?? FuelSavingsSettings.defaultMPG
+        let amount = loadString(service: fuelSavingsAmountKey).flatMap(Double.init) ?? FuelSavingsSettings.defaultPreferredAmount.value
+        let unit = loadString(service: fuelSavingsUnitKey).flatMap(FuelSavingsFillUnit.init(rawValue:)) ?? FuelSavingsSettings.defaultPreferredAmount.unit
+#if DEBUG
+        // The two stores are mirrors and can DISAGREE (the keychain survives
+        // app deletion, the app-group defaults do not). Print both raw copies
+        // plus which one won, so a setting that flips between launches is
+        // diagnosable instead of guesswork.
+        func raw(_ service: String) -> (keychain: String, appGroup: String) {
+            let keychain = keychainData(service: service).flatMap { String(data: $0, encoding: .utf8) } ?? "-"
+            let appGroup = UserDefaults(suiteName: appGroupSuite)?.string(forKey: service) ?? "-"
+            return (keychain, appGroup)
+        }
+        let enabledRaw = raw(fuelSavingsEnabledKey)
+        let mpgRaw = raw(fuelSavingsMPGKey)
+        print("FB-SAVINGS read enabled=\(enabled ? 1 : 0) [kc=\(enabledRaw.keychain) ag=\(enabledRaw.appGroup)] mpg=\(mpg) [kc=\(mpgRaw.keychain) ag=\(mpgRaw.appGroup)]")
+#endif
+        return FuelSavingsSettings(
+            enabled: enabled,
+            mpg: mpg,
+            preferredAmount: FuelSavingsFillAmount(value: amount, unit: unit)
+        )
+    }
+
+    static func saveFuelSavingsSettings(_ settings: FuelSavingsSettings) {
+        saveString(settings.enabled ? "1" : "0", service: fuelSavingsEnabledKey)
+        saveString(String(settings.mpg), service: fuelSavingsMPGKey)
+        saveString(String(settings.preferredAmount.value), service: fuelSavingsAmountKey)
+        saveString(settings.preferredAmount.unit.rawValue, service: fuelSavingsUnitKey)
+    }
+
     /// Superscript digit glyphs for the pounds & pence format's small raised
     /// third digit (the forecourt style: "£1.29⁹").
     private static let superscriptDigits: [Character] = ["⁰", "¹", "²", "³", "⁴", "⁵", "⁶", "⁷", "⁸", "⁹"]
@@ -1148,20 +1224,41 @@ struct FuelStore {
     /// catches any real pin change.
     static let roadDistancePinToleranceDegrees: Double = 1e-4
 
+    /// In-memory copy of the road-distance cache.
+    ///
+    /// `loadRoadDistances()` reads the KEYCHAIN — a synchronous `securityd` XPC
+    /// round-trip plus a full base64+JSON decode — and `displayDistanceKM` is
+    /// called PER STATION inside comparisons (`min(by:)`, `sorted`). Re-reading
+    /// it on every call meant tens of thousands of synchronous XPC round-trips
+    /// on the main thread during scene creation, which stalled past the 20 s iOS
+    /// launch watchdog and got the app SIGKILLed (0x8BADF00D). Decode once per
+    /// process, reuse, and refresh on save.
+    private static var roadDistanceMemo: RoadDistanceCache?
+    /// Distinguishes "not loaded yet" from "loaded, and there is no cache".
+    private static var roadDistanceMemoLoaded = false
     static func saveRoadDistances(sourceLat: Double, sourceLng: Double, entries: [String: CachedRoadDistance]) {
         let cache = RoadDistanceCache(sourceLat: sourceLat, sourceLng: sourceLng,
                                       updatedAt: Date().timeIntervalSince1970, entries: entries)
         if let data = try? JSONEncoder().encode(cache) {
             saveString(data.base64EncodedString(), service: roadDistancesKey)
         }
+        roadDistanceMemo = cache
+        roadDistanceMemoLoaded = true
     }
 
     static func loadRoadDistances() -> RoadDistanceCache? {
-        guard let raw = loadString(service: roadDistancesKey),
-              let data = Data(base64Encoded: raw),
-              let cache = try? JSONDecoder().decode(RoadDistanceCache.self, from: data)
-        else { return nil }
-        return cache
+        if roadDistanceMemoLoaded { return roadDistanceMemo }
+        let decoded: RoadDistanceCache?
+        if let raw = loadString(service: roadDistancesKey),
+           let data = Data(base64Encoded: raw),
+           let cache = try? JSONDecoder().decode(RoadDistanceCache.self, from: data) {
+            decoded = cache
+        } else {
+            decoded = nil
+        }
+        roadDistanceMemo = decoded
+        roadDistanceMemoLoaded = true
+        return decoded
     }
 
     /// Cached road distance (metres) to a station from the user's location, or
@@ -1169,6 +1266,26 @@ struct FuelStore {
     /// is now / the station's own pin doesn't match the coordinate that was
     /// routed.
     static func roadDistanceMeters(for station: FuelStation, userLat: Double, userLng: Double) -> Double? {
+        roadDistanceEntry(for: station, userLat: userLat, userLng: userLng)?.meters
+    }
+
+    /// Complete out-and-back routed journey distance (metres). New caches store
+    /// the return route separately because Apple Maps may choose a different
+    /// return path; legacy one-way caches safely fall back to doubling outward.
+    static func roadJourneyMeters(for station: FuelStation, userLat: Double, userLng: Double) -> Double? {
+        guard let entry = roadDistanceEntry(for: station, userLat: userLat, userLng: userLng) else { return nil }
+        return entry.meters + (entry.returnMeters ?? entry.meters)
+    }
+
+    /// Whether a usable routed distance is already cached for this station from
+    /// (near enough) this origin. The routing pass uses it to spend its per-pass
+    /// budget on stations that still need a route instead of re-routing the
+    /// same nearest handful forever.
+    static func hasRoadDistance(for station: FuelStation, userLat: Double, userLng: Double) -> Bool {
+        roadDistanceEntry(for: station, userLat: userLat, userLng: userLng) != nil
+    }
+
+    private static func roadDistanceEntry(for station: FuelStation, userLat: Double, userLng: Double) -> CachedRoadDistance? {
         guard let cache = loadRoadDistances(),
               let entry = cache.entries[station.id] else { return nil }
         // The cache is only valid near the location it was built from.
@@ -1185,7 +1302,7 @@ struct FuelStore {
         // live / cached station sets from injecting each other's road metres.
         guard abs(entry.lat - station.lat) <= roadDistancePinToleranceDegrees,
               abs(entry.lng - station.lng) <= roadDistancePinToleranceDegrees else { return nil }
-        return entry.meters
+        return entry
     }
 
     /// Distance (km) to display for a station: cached ROAD distance when
@@ -1266,6 +1383,14 @@ struct CachedRoadDistance: Codable {
     let meters: Double
     let lat: Double
     let lng: Double
+    let returnMeters: Double?
+
+    init(meters: Double, lat: Double, lng: Double, returnMeters: Double? = nil) {
+        self.meters = meters
+        self.lat = lat
+        self.lng = lng
+        self.returnMeters = returnMeters
+    }
 }
 
 /// `FuelStore.roadDistancesKey`). `entries` maps stationID → road metres +
diff --git a/Shared/MirrorFuelProvider.swift b/Shared/MirrorFuelProvider.swift
index 3ff3410..f40e465 100644
--- a/Shared/MirrorFuelProvider.swift
+++ b/Shared/MirrorFuelProvider.swift
@@ -81,6 +81,14 @@ struct MirrorFuelProvider: FuelPriceProviding {
         )
     }
 
+    static func cachedStations(near lat: Double? = nil, lng: Double? = nil,
+                               fuel: FuelType = .e10, radiusKM: Double? = nil) -> [FuelStation]? {
+        guard let cache = loadDumpCache(),
+              let stations = try? FuelPriceProvider.decodeStations(from: cache.data) else { return nil }
+        latestMeta = FuelPriceProvider.decodeRelayMeta(from: cache.data)
+        return focused(stations, near: lat, lng: lng, fuel: fuel, radiusKM: radiusKM)
+    }
+
     func fetchStations(near lat: Double?, lng: Double?, fuel: FuelType, radiusKM: Double?) async throws -> [FuelStation] {
         // 1. Tiny pointer fetch — the freshest snapshot day.
         guard let latest = await FuelHistoryStore.fetchLatest(base: baseURL),
@@ -104,10 +112,16 @@ struct MirrorFuelProvider: FuelPriceProviding {
                 throw FuelProviderError.mirrorUnavailable
             }
             Self.saveDumpCache(day: day, data: fetched)
+            #if DEBUG
+            print("FB-STORAGE dump cached day=\(day) bytes=\(fetched.count) reuse=\(Self.canReuseCache(cachedDay: Self.loadDumpCache()?.day, latestDay: day))")
+            #endif
             data = fetched
         }
         let stations = try FuelPriceProvider.decodeStations(from: data)
         Self.latestMeta = FuelPriceProvider.decodeRelayMeta(from: data)
+        #if DEBUG
+        print("FB-MIRROR day=\(day) bytes=\(data.count) decoded=\(stations.count)")
+        #endif
         return Self.focused(stations, near: lat, lng: lng, fuel: fuel, radiusKM: radiusKM)
     }
 }