diff --git a/Sources/CodexBar/PreferencesGeneralPane.swift b/Sources/CodexBar/PreferencesGeneralPane.swift
index 39a95a55f..72b13d6a1 100644
--- a/Sources/CodexBar/PreferencesGeneralPane.swift
+++ b/Sources/CodexBar/PreferencesGeneralPane.swift
@@ -96,6 +96,13 @@ struct GeneralPane: View {
                         subtitle: "Notifies when the 5-hour session quota hits 0% and when it becomes " +
                             "available again.",
                         binding: self.$settings.sessionQuotaNotificationsEnabled)
+                    PreferenceToggleRow(
+                        title: "Quota warning notifications",
+                        subtitle: "Warns before quota runs out. Fires once per threshold per window.",
+                        binding: self.$settings.quotaWarningNotificationsEnabled)
+                    if self.settings.quotaWarningNotificationsEnabled {
+                        QuotaWarningThresholdPicker(settings: self.settings)
+                    }
                 }
 
                 Divider()
@@ -163,3 +170,35 @@ struct GeneralPane: View {
             .foregroundStyle(.tertiary)
     }
 }
+
+@MainActor
+private struct QuotaWarningThresholdPicker: View {
+    @Bindable var settings: SettingsStore
+
+    private static let availableThresholds = [80, 50, 20, 10]
+
+    var body: some View {
+        VStack(alignment: .leading, spacing: 4) {
+            Text("Warn at these remaining levels:")
+                .font(.footnote)
+                .foregroundStyle(.secondary)
+            HStack(spacing: 8) {
+                ForEach(Self.availableThresholds, id: \.self) { threshold in
+                    Toggle("\(threshold)%", isOn: Binding(
+                        get: { self.settings.quotaWarningThresholds.contains(threshold) },
+                        set: { isOn in
+                            var current = self.settings.quotaWarningThresholds
+                            if isOn {
+                                if !current.contains(threshold) { current.append(threshold) }
+                            } else {
+                                current.removeAll { $0 == threshold }
+                            }
+                            self.settings.quotaWarningThresholds = current.sorted(by: >)
+                        }))
+                    .toggleStyle(.checkbox)
+                }
+            }
+        }
+        .padding(.leading, 20)
+    }
+}
diff --git a/Sources/CodexBar/QuotaWarningNotifications.swift b/Sources/CodexBar/QuotaWarningNotifications.swift
new file mode 100644
index 000000000..b80edb8fb
--- /dev/null
+++ b/Sources/CodexBar/QuotaWarningNotifications.swift
@@ -0,0 +1,67 @@
+import CodexBarCore
+import Foundation
+
+enum QuotaWarningWindow: String, Sendable {
+    case primary
+    case secondary
+}
+
+struct QuotaWarningEvent: Equatable, Sendable {
+    let threshold: Int
+    let window: QuotaWarningWindow
+    let currentRemaining: Double
+}
+
+enum QuotaWarningNotificationLogic {
+    /// Returns thresholds that were newly crossed downward.
+    /// A threshold is considered crossed when `previousRemaining > threshold` and
+    /// `currentRemaining <= threshold`, and the threshold has not already fired.
+    static func crossedThresholds(
+        previousRemaining: Double?,
+        currentRemaining: Double,
+        thresholds: [Int],
+        alreadyFired: Set<Int>
+    ) -> [Int] {
+        guard let previousRemaining else { return [] }
+
+        var crossed: [Int] = []
+        for threshold in thresholds {
+            let t = Double(threshold)
+            if previousRemaining > t,
+               currentRemaining <= t,
+               !alreadyFired.contains(threshold)
+            {
+                crossed.append(threshold)
+            }
+        }
+        return crossed
+    }
+
+    /// Returns thresholds that should be cleared from `alreadyFired` because
+    /// the remaining percentage has risen back above them.
+    static func restoredThresholds(
+        currentRemaining: Double,
+        alreadyFired: Set<Int>
+    ) -> Set<Int> {
+        Set(alreadyFired.filter { Double($0) < currentRemaining })
+    }
+}
+
+@MainActor
+final class QuotaWarningNotifier {
+    private let logger = CodexBarLog.logger(LogCategories.quotaWarningNotifications)
+
+    init() {}
+
+    func post(event: QuotaWarningEvent, provider: UsageProvider) {
+        let providerName = ProviderDescriptorRegistry.descriptor(for: provider).metadata.displayName
+        let windowLabel = event.window == .primary ? "session" : "weekly"
+
+        let title = "\(providerName) \(windowLabel) quota low"
+        let body = "\(event.threshold)% remaining – currently at \(Int(event.currentRemaining))%."
+
+        let idPrefix = "quota-warning-\(provider.rawValue)-\(event.window.rawValue)-\(event.threshold)"
+        self.logger.info("enqueuing", metadata: ["prefix": idPrefix])
+        AppNotifications.shared.post(idPrefix: idPrefix, title: title, body: body)
+    }
+}
diff --git a/Sources/CodexBar/SettingsStore+Defaults.swift b/Sources/CodexBar/SettingsStore+Defaults.swift
index 44d83a023..1e0f3d1c7 100644
--- a/Sources/CodexBar/SettingsStore+Defaults.swift
+++ b/Sources/CodexBar/SettingsStore+Defaults.swift
@@ -101,6 +101,22 @@ extension SettingsStore {
         }
     }
 
+    var quotaWarningNotificationsEnabled: Bool {
+        get { self.defaultsState.quotaWarningNotificationsEnabled }
+        set {
+            self.defaultsState.quotaWarningNotificationsEnabled = newValue
+            self.userDefaults.set(newValue, forKey: "quotaWarningNotificationsEnabled")
+        }
+    }
+
+    var quotaWarningThresholds: [Int] {
+        get { self.defaultsState.quotaWarningThresholdsRaw }
+        set {
+            self.defaultsState.quotaWarningThresholdsRaw = newValue
+            self.userDefaults.set(newValue, forKey: "quotaWarningThresholds")
+        }
+    }
+
     var usageBarsShowUsed: Bool {
         get { self.defaultsState.usageBarsShowUsed }
         set {
diff --git a/Sources/CodexBar/SettingsStore.swift b/Sources/CodexBar/SettingsStore.swift
index 09f3e3caa..0dd818e6d 100644
--- a/Sources/CodexBar/SettingsStore.swift
+++ b/Sources/CodexBar/SettingsStore.swift
@@ -184,6 +184,10 @@ extension SettingsStore {
         if sessionQuotaDefault == nil {
             userDefaults.set(true, forKey: "sessionQuotaNotificationsEnabled")
         }
+        let quotaWarningNotificationsEnabled = userDefaults.object(
+            forKey: "quotaWarningNotificationsEnabled") as? Bool ?? false
+        let quotaWarningThresholdsRaw = userDefaults.array(
+            forKey: "quotaWarningThresholds") as? [Int] ?? [50, 20]
         let usageBarsShowUsed = userDefaults.object(forKey: "usageBarsShowUsed") as? Bool ?? false
         let resetTimesShowAbsolute = userDefaults.object(forKey: "resetTimesShowAbsolute") as? Bool ?? false
         let menuBarShowsBrandIconWithPercent = userDefaults.object(
@@ -235,6 +239,8 @@ extension SettingsStore {
             debugKeepCLISessionsAlive: debugKeepCLISessionsAlive,
             statusChecksEnabled: statusChecksEnabled,
             sessionQuotaNotificationsEnabled: sessionQuotaNotificationsEnabled,
+            quotaWarningNotificationsEnabled: quotaWarningNotificationsEnabled,
+            quotaWarningThresholdsRaw: quotaWarningThresholdsRaw,
             usageBarsShowUsed: usageBarsShowUsed,
             resetTimesShowAbsolute: resetTimesShowAbsolute,
             menuBarShowsBrandIconWithPercent: menuBarShowsBrandIconWithPercent,
diff --git a/Sources/CodexBar/SettingsStoreState.swift b/Sources/CodexBar/SettingsStoreState.swift
index ff3d640bd..256e520a0 100644
--- a/Sources/CodexBar/SettingsStoreState.swift
+++ b/Sources/CodexBar/SettingsStoreState.swift
@@ -11,6 +11,8 @@ struct SettingsDefaultsState: Sendable {
     var debugKeepCLISessionsAlive: Bool
     var statusChecksEnabled: Bool
     var sessionQuotaNotificationsEnabled: Bool
+    var quotaWarningNotificationsEnabled: Bool
+    var quotaWarningThresholdsRaw: [Int]
     var usageBarsShowUsed: Bool
     var resetTimesShowAbsolute: Bool
     var menuBarShowsBrandIconWithPercent: Bool
diff --git a/Sources/CodexBar/UsageStore+Refresh.swift b/Sources/CodexBar/UsageStore+Refresh.swift
index 1e60dfb37..1dc4c1ee0 100644
--- a/Sources/CodexBar/UsageStore+Refresh.swift
+++ b/Sources/CodexBar/UsageStore+Refresh.swift
@@ -25,6 +25,8 @@ extension UsageStore {
                 self.statuses.removeValue(forKey: provider)
                 self.lastKnownSessionRemaining.removeValue(forKey: provider)
                 self.lastKnownSessionWindowSource.removeValue(forKey: provider)
+                self.lastKnownSecondaryRemaining.removeValue(forKey: provider)
+                self.quotaWarningFiredThresholds.removeValue(forKey: provider)
                 self.lastTokenFetchAt.removeValue(forKey: provider)
             }
             return
@@ -79,6 +81,7 @@ extension UsageStore {
         case let .success(result):
             let scoped = result.usage.scoped(to: provider)
             await MainActor.run {
+                self.handleQuotaWarningTransition(provider: provider, snapshot: scoped)
                 self.handleSessionQuotaTransition(provider: provider, snapshot: scoped)
                 self.snapshots[provider] = scoped
                 self.lastSourceLabels[provider] = result.sourceLabel
diff --git a/Sources/CodexBar/UsageStore+TokenAccounts.swift b/Sources/CodexBar/UsageStore+TokenAccounts.swift
index 3e55ffa9f..fb6d69fce 100644
--- a/Sources/CodexBar/UsageStore+TokenAccounts.swift
+++ b/Sources/CodexBar/UsageStore+TokenAccounts.swift
@@ -156,6 +156,11 @@ extension UsageStore {
                 scoped
             }
             await MainActor.run {
+                if let account, self.lastWarningAccountID[provider] != account.id {
+                    self.resetQuotaWarningState(for: provider)
+                    self.lastWarningAccountID[provider] = account.id
+                }
+                self.handleQuotaWarningTransition(provider: provider, snapshot: labeled)
                 self.handleSessionQuotaTransition(provider: provider, snapshot: labeled)
                 self.snapshots[provider] = labeled
                 self.lastSourceLabels[provider] = result.sourceLabel
diff --git a/Sources/CodexBar/UsageStore.swift b/Sources/CodexBar/UsageStore.swift
index e3f0bcae4..7d84a807b 100644
--- a/Sources/CodexBar/UsageStore.swift
+++ b/Sources/CodexBar/UsageStore.swift
@@ -39,6 +39,8 @@ extension UsageStore {
             _ = self.settings.refreshFrequency
             _ = self.settings.statusChecksEnabled
             _ = self.settings.sessionQuotaNotificationsEnabled
+            _ = self.settings.quotaWarningNotificationsEnabled
+            _ = self.settings.quotaWarningThresholds
             _ = self.settings.usageBarsShowUsed
             _ = self.settings.costUsageEnabled
             _ = self.settings.randomBlinkEnabled
@@ -152,6 +154,11 @@ final class UsageStore {
     @ObservationIgnored var codexHistoricalDatasetAccountKey: String?
     @ObservationIgnored var lastKnownSessionRemaining: [UsageProvider: Double] = [:]
     @ObservationIgnored var lastKnownSessionWindowSource: [UsageProvider: SessionQuotaWindowSource] = [:]
+    @ObservationIgnored var lastKnownSecondaryRemaining: [UsageProvider: Double] = [:]
+    @ObservationIgnored var quotaWarningFiredThresholds: [UsageProvider: [QuotaWarningWindow: Set<Int>]] = [:]
+    @ObservationIgnored var lastWarningAccountID: [UsageProvider: UUID] = [:]
+    @ObservationIgnored private let quotaWarningNotifier: QuotaWarningNotifier
+    @ObservationIgnored private let quotaWarningLogger = CodexBarLog.logger(LogCategories.quotaWarning)
     @ObservationIgnored var lastTokenFetchAt: [UsageProvider: Date] = [:]
     @ObservationIgnored private var hasCompletedInitialRefresh: Bool = false
     @ObservationIgnored private let tokenFetchTTL: TimeInterval = 60 * 60
@@ -167,6 +174,7 @@ final class UsageStore {
         registry: ProviderRegistry = .shared,
         historicalUsageHistoryStore: HistoricalUsageHistoryStore = HistoricalUsageHistoryStore(),
         sessionQuotaNotifier: any SessionQuotaNotifying = SessionQuotaNotifier(),
+        quotaWarningNotifier: QuotaWarningNotifier = QuotaWarningNotifier(),
         startupBehavior: StartupBehavior = .automatic)
     {
         self.codexFetcher = fetcher
@@ -177,6 +185,7 @@ final class UsageStore {
         self.registry = registry
         self.historicalUsageHistoryStore = historicalUsageHistoryStore
         self.sessionQuotaNotifier = sessionQuotaNotifier
+        self.quotaWarningNotifier = quotaWarningNotifier
         self.startupBehavior = startupBehavior.resolved(isRunningTests: Self.isRunningTestsProcess())
         self.providerMetadata = registry.metadata
         self
@@ -589,6 +598,87 @@ final class UsageStore {
         self.sessionQuotaNotifier.post(transition: transition, provider: provider, badge: nil)
     }
 
+    func handleQuotaWarningTransition(provider: UsageProvider, snapshot: UsageSnapshot) {
+        // Always update tracking state so baselines stay current even when
+        // notifications are disabled. This prevents retroactive alerts when
+        // the user re-enables notifications after quota has dropped.
+        defer {
+            if let secondary = snapshot.secondary {
+                self.lastKnownSecondaryRemaining[provider] = secondary.remainingPercent
+            }
+        }
+
+        guard self.settings.quotaWarningNotificationsEnabled else { return }
+        let thresholds = self.settings.quotaWarningThresholds.sorted(by: >)
+        guard !thresholds.isEmpty else { return }
+
+        if let primary = snapshot.primary {
+            self.processWarningWindow(
+                provider: provider,
+                window: .primary,
+                currentRemaining: primary.remainingPercent,
+                previousRemaining: self.lastKnownSessionRemaining[provider],
+                thresholds: thresholds)
+        }
+
+        if let secondary = snapshot.secondary {
+            self.processWarningWindow(
+                provider: provider,
+                window: .secondary,
+                currentRemaining: secondary.remainingPercent,
+                previousRemaining: self.lastKnownSecondaryRemaining[provider],
+                thresholds: thresholds)
+        }
+    }
+
+    /// Resets quota warning baselines and fired thresholds for a provider.
+    /// Call when the selected token account changes to avoid false alerts
+    /// caused by a different account's remaining quota.
+    func resetQuotaWarningState(for provider: UsageProvider) {
+        self.lastKnownSecondaryRemaining.removeValue(forKey: provider)
+        self.quotaWarningFiredThresholds.removeValue(forKey: provider)
+    }
+
+    private func processWarningWindow(
+        provider: UsageProvider,
+        window: QuotaWarningWindow,
+        currentRemaining: Double,
+        previousRemaining: Double?,
+        thresholds: [Int])
+    {
+        var firedSet = self.quotaWarningFiredThresholds[provider]?[window] ?? []
+
+        let restored = QuotaWarningNotificationLogic.restoredThresholds(
+            currentRemaining: currentRemaining, alreadyFired: firedSet)
+        firedSet.subtract(restored)
+
+        let crossed = QuotaWarningNotificationLogic.crossedThresholds(
+            previousRemaining: previousRemaining,
+            currentRemaining: currentRemaining,
+            thresholds: thresholds,
+            alreadyFired: firedSet)
+
+        for threshold in crossed {
+            let event = QuotaWarningEvent(
+                threshold: threshold, window: window, currentRemaining: currentRemaining)
+            self.quotaWarningLogger.info(
+                "threshold crossed",
+                metadata: [
+                    "provider": provider.rawValue,
+                    "window": window.rawValue,
+                    "threshold": "\(threshold)",
+                    "remaining": "\(currentRemaining)",
+                ])
+            self.quotaWarningNotifier.post(event: event, provider: provider)
+            firedSet.insert(threshold)
+        }
+
+        if self.quotaWarningFiredThresholds[provider] == nil {
+            self.quotaWarningFiredThresholds[provider] = [:]
+        }
+        self.quotaWarningFiredThresholds[provider]?[window] = firedSet
+    }
+
     private func refreshStatus(_ provider: UsageProvider) async {
         guard self.settings.statusChecksEnabled else { return }
         guard let meta = self.providerMetadata[provider] else { return }
diff --git a/Sources/CodexBarCore/Logging/LogCategories.swift b/Sources/CodexBarCore/Logging/LogCategories.swift
index 37a7726ef..352839f62 100644
--- a/Sources/CodexBarCore/Logging/LogCategories.swift
+++ b/Sources/CodexBarCore/Logging/LogCategories.swift
@@ -45,6 +45,8 @@ public enum LogCategories {
     public static let openRouterUsage = "openrouter-usage"
     public static let providerDetection = "provider-detection"
     public static let providers = "providers"
+    public static let quotaWarning = "quotaWarning"
+    public static let quotaWarningNotifications = "quotaWarningNotifications"
     public static let sessionQuota = "sessionQuota"
     public static let sessionQuotaNotifications = "sessionQuotaNotifications"
     public static let settings = "settings"
diff --git a/Tests/CodexBarTests/QuotaWarningNotificationLogicTests.swift b/Tests/CodexBarTests/QuotaWarningNotificationLogicTests.swift
new file mode 100644
index 000000000..052a68e37
--- /dev/null
+++ b/Tests/CodexBarTests/QuotaWarningNotificationLogicTests.swift
@@ -0,0 +1,93 @@
+import Testing
+@testable import CodexBar
+
+@Suite
+struct QuotaWarningNotificationLogicTests {
+    @Test
+    func doesNothingWithoutPreviousValue() {
+        let crossed = QuotaWarningNotificationLogic.crossedThresholds(
+            previousRemaining: nil, currentRemaining: 40,
+            thresholds: [80, 50, 20], alreadyFired: [])
+        #expect(crossed.isEmpty)
+    }
+
+    @Test
+    func detectsSingleThresholdCrossing() {
+        let crossed = QuotaWarningNotificationLogic.crossedThresholds(
+            previousRemaining: 55, currentRemaining: 45,
+            thresholds: [80, 50, 20], alreadyFired: [])
+        #expect(crossed == [50])
+    }
+
+    @Test
+    func detectsMultipleThresholdCrossings() {
+        let crossed = QuotaWarningNotificationLogic.crossedThresholds(
+            previousRemaining: 55, currentRemaining: 15,
+            thresholds: [80, 50, 20], alreadyFired: [])
+        #expect(crossed == [50, 20])
+    }
+
+    @Test
+    func doesNotRefireAlreadyFiredThreshold() {
+        let crossed = QuotaWarningNotificationLogic.crossedThresholds(
+            previousRemaining: 55, currentRemaining: 45,
+            thresholds: [80, 50, 20], alreadyFired: [50])
+        #expect(crossed.isEmpty)
+    }
+
+    @Test
+    func clearsRestoredThresholds() {
+        let restored = QuotaWarningNotificationLogic.restoredThresholds(
+            currentRemaining: 60, alreadyFired: [80, 50, 20])
+        #expect(restored == [50, 20])
+    }
+
+    @Test
+    func doesNotCrossOnUpwardMovement() {
+        let crossed = QuotaWarningNotificationLogic.crossedThresholds(
+            previousRemaining: 45, currentRemaining: 55,
+            thresholds: [80, 50, 20], alreadyFired: [])
+        #expect(crossed.isEmpty)
+    }
+
+    @Test
+    func handlesExactThresholdBoundary() {
+        let crossed = QuotaWarningNotificationLogic.crossedThresholds(
+            previousRemaining: 50.001, currentRemaining: 50.0,
+            thresholds: [80, 50, 20], alreadyFired: [])
+        #expect(crossed == [50])
+    }
+
+    @Test
+    func handlesEmptyThresholds() {
+        let crossed = QuotaWarningNotificationLogic.crossedThresholds(
+            previousRemaining: 80, currentRemaining: 10,
+            thresholds: [], alreadyFired: [])
+        #expect(crossed.isEmpty)
+    }
+
+    @Test
+    func doesNotCrossWhenStayingAboveThreshold() {
+        let crossed = QuotaWarningNotificationLogic.crossedThresholds(
+            previousRemaining: 90, currentRemaining: 85,
+            thresholds: [80, 50, 20], alreadyFired: [])
+        #expect(crossed.isEmpty)
+    }
+
+    @Test
+    func doesNotRestoreThresholdAboveCurrentRemaining() {
+        let restored = QuotaWarningNotificationLogic.restoredThresholds(
+            currentRemaining: 60, alreadyFired: [80, 50, 20])
+        #expect(!restored.contains(80))
+        #expect(restored.contains(50))
+        #expect(restored.contains(20))
+    }
+
+    @Test
+    func crossesAllThresholdsOnLargeDrop() {
+        let crossed = QuotaWarningNotificationLogic.crossedThresholds(
+            previousRemaining: 100, currentRemaining: 5,
+            thresholds: [80, 50, 20], alreadyFired: [])
+        #expect(crossed == [80, 50, 20])
+    }
+}