diff --git a/apps/mobile/lib/api.dart b/apps/mobile/lib/api.dart
index faf3011..aa46a27 100644
--- a/apps/mobile/lib/api.dart
+++ b/apps/mobile/lib/api.dart
@@ -25,6 +25,14 @@ class Api {
   final FlutterSecureStorage _storage = const FlutterSecureStorage();
   String? token;
 
+  /// Last successful GET response per path. Screens seed their state from it so
+  /// switching tabs shows data instantly while a fresh copy loads behind it.
+  final Map<String, Map<String, dynamic>> _cache = {};
+
+  Map<String, dynamic>? peek(String path) => _cache[path];
+
+  void clearCache() => _cache.clear();
+
   Future<File> _sessionFile() async {
     final dir = await getApplicationSupportDirectory();
     if (!await dir.exists()) {
@@ -109,6 +117,8 @@ class Api {
 
   Future<void> setToken(String? value) async {
     token = value;
+    // Login, logout and session expiry change whose data the cache holds.
+    clearCache();
     try {
       if (value == null) {
         await _storage.delete(key: 'token');
@@ -176,6 +186,7 @@ class Api {
     if (sent.statusCode >= 400) {
       throw ApiException(data['error'] as String? ?? 'server_error', statusCode: sent.statusCode);
     }
+    if (method.toUpperCase() == 'GET') _cache[path] = data;
     return data;
   }
 }
diff --git a/apps/mobile/lib/main.dart b/apps/mobile/lib/main.dart
index 665857e..319d5be 100644
--- a/apps/mobile/lib/main.dart
+++ b/apps/mobile/lib/main.dart
@@ -969,8 +969,8 @@ class TodayScreen extends StatefulWidget {
 const _meals = ['breakfast', 'lunch', 'dinner', 'snacks'];
 
 class _TodayScreenState extends State<TodayScreen> {
-  Map<String, dynamic>? day;
-  Map<String, dynamic>? fasting;
+  late Map<String, dynamic>? day = widget.api.peek('/api/days/today');
+  late Map<String, dynamic>? fasting = widget.api.peek('/api/fasting');
   String error = '';
   Timer? ticker;
 
@@ -1020,6 +1020,7 @@ class _TodayScreenState extends State<TodayScreen> {
   void initState() {
     super.initState();
     AppleHealth.synced.addListener(_onHealthSynced);
+    _ensureTicker();
     unawaited(load());
   }
 
@@ -2004,7 +2005,7 @@ class FastingScreen extends StatefulWidget {
 }
 
 class _FastingScreenState extends State<FastingScreen> {
-  Map<String, dynamic>? fasting;
+  late Map<String, dynamic>? fasting = widget.api.peek('/api/fasting');
   String error = '';
   Timer? ticker;
 
@@ -2250,7 +2251,7 @@ class WeekScreen extends StatefulWidget {
 }
 
 class _WeekScreenState extends State<WeekScreen> {
-  Map<String, dynamic>? week;
+  late Map<String, dynamic>? week = widget.api.peek('/api/weeks');
   String? on;
 
   @override
@@ -2260,8 +2261,11 @@ class _WeekScreenState extends State<WeekScreen> {
   }
 
   Future<void> load() async {
-    final query = on == null ? '' : '?on=$on';
-    final data = await widget.api.send('GET', '/api/weeks$query');
+    final path = '/api/weeks${on == null ? '' : '?on=$on'}';
+    final cached = widget.api.peek(path);
+    if (cached != null && week != cached) setState(() => week = cached);
+    final data = await widget.api.send('GET', path);
+    if (!mounted || path != '/api/weeks${on == null ? '' : '?on=$on'}') return;
     setState(() => week = data);
   }
 
@@ -2548,7 +2552,9 @@ class WeightScreen extends StatefulWidget {
 }
 
 class _WeightScreenState extends State<WeightScreen> {
-  List<Map<String, dynamic>> weights = [];
+  late List<Map<String, dynamic>> weights =
+      ((widget.api.peek('/api/weights')?['weights'] as List?) ?? const [])
+          .cast<Map<String, dynamic>>();
   final controller = TextEditingController();
   String error = '';
 
@@ -2759,11 +2765,17 @@ class SettingsScreen extends StatefulWidget {
 }
 
 class _SettingsScreenState extends State<SettingsScreen> {
-  Map<String, dynamic>? profile;
-  Map<String, dynamic>? fasting;
-  Map<String, dynamic>? healthState;
-  final stepGoal = TextEditingController();
-  final exerciseGoal = TextEditingController();
+  late Map<String, dynamic>? profile =
+      (widget.api.peek('/api/profile')?['profile'] as Map?)
+          ?.cast<String, dynamic>();
+  late Map<String, dynamic>? fasting = widget.api.peek('/api/fasting');
+  late Map<String, dynamic>? healthState = widget.api.peek('/api/apple-health');
+  late final stepGoal = TextEditingController(
+    text: healthState == null ? '' : '${healthState!['stepGoal']}',
+  );
+  late final exerciseGoal = TextEditingController(
+    text: healthState == null ? '' : '${healthState!['exerciseGoalMinutes']}',
+  );
   String healthError = '';
   bool healthBusy = false;
   bool autoPublish = false;
@@ -3602,6 +3614,14 @@ class _PermissionsScreenState extends State<PermissionsScreen> {
   @override
   void initState() {
     super.initState();
+    final cached = widget.api.peek('/api/rbac/permissions');
+    if (cached != null) {
+      operations = ((cached['operations'] as List?) ?? []).cast<String>();
+      permissions = ((cached['permissions'] as Map?) ?? {}).map(
+        (key, value) => MapEntry(key.toString(), value == true),
+      );
+      loading = false;
+    }
     unawaited(load());
   }
 
diff --git a/apps/web/src/App.tsx b/apps/web/src/App.tsx
index 05c8ffa..a0605f6 100644
--- a/apps/web/src/App.tsx
+++ b/apps/web/src/App.tsx
@@ -3,6 +3,7 @@ import { createPortal } from "react-dom";
 import { Link, NavLink, Navigate, Route, Routes, useLocation, useNavigate, useParams, useSearchParams } from "react-router-dom";
 import {
   api,
+  peek,
   ApiError,
   type AppleHealthState,
   type DayEntry,
@@ -459,11 +460,11 @@ const MEAL_COLOR: Record<MealCategory, string> = {
 
 function Today({ canVerifyFoods, onFastingChange }: { canVerifyFoods: boolean; onFastingChange: () => void }) {
   const { t } = useI18n();
-  const [loadedDay, setDay] = useState<DayResponse | null>(null);
+  const [loadedDay, setDay] = useState<DayResponse | null>(() => peek<DayResponse>("/api/days/today"));
   // Removed entry waiting out its Undo window; deleted on the server afterwards.
   const [pendingRemoval, setPendingRemoval] = useState<DayEntry | null>(null);
   const removalTimer = useRef<number | null>(null);
-  const [fasting, setFasting] = useState<FastingState | null>(null);
+  const [fasting, setFasting] = useState<FastingState | null>(() => peek<FastingState>("/api/fasting"));
   const [now, setNow] = useState(Date.now());
   const [loggingMeal, setLoggingMeal] = useState<MealCategory | null>(null);
   const [query, setQuery] = useState("");
@@ -878,7 +879,7 @@ function mealLabel(t: Copy, meal: MealCategory) {
 
 function FastingPage({ onFastingChange }: { onFastingChange: () => void }) {
   const { t } = useI18n();
-  const [fasting, setFasting] = useState<FastingState | null>(null);
+  const [fasting, setFasting] = useState<FastingState | null>(() => peek<FastingState>("/api/fasting"));
   const [error, setError] = useState("");
   const [now, setNow] = useState(Date.now());
 
@@ -1102,12 +1103,14 @@ function WeekPage() {
   const { t } = useI18n();
   const [params, setParams] = useSearchParams();
   const on = params.get("on") ?? "";
-  const [week, setWeek] = useState<WeekResponse | null>(null);
+  const weekPath = `/api/weeks${on ? `?on=${on}` : ""}`;
+  const [week, setWeek] = useState<WeekResponse | null>(() => peek<WeekResponse>(weekPath));
   const [error, setError] = useState("");
   useEffect(() => {
-    const query = on ? `?on=${on}` : "";
-    api<WeekResponse>(`/api/weeks${query}`).then(setWeek).catch((err) => setError(message(t, err)));
-  }, [on, t]);
+    const cached = peek<WeekResponse>(weekPath);
+    if (cached) setWeek(cached);
+    api<WeekResponse>(weekPath).then(setWeek).catch((err) => setError(message(t, err)));
+  }, [weekPath, t]);
   if (!week) return error ? <p className="error">{error}</p> : <p className="muted loading">…</p>;
   const today = todayJerusalemDay();
   const isCurrentWeek = addDays(week.sunday, 7) > today;
@@ -1176,7 +1179,7 @@ function formatKcal(value: number): string {
 
 function WeightPage() {
   const { t } = useI18n();
-  const [weights, setWeights] = useState<WeightPoint[]>([]);
+  const [weights, setWeights] = useState<WeightPoint[]>(() => peek<{ weights: WeightPoint[] }>("/api/weights")?.weights ?? []);
   const [error, setError] = useState("");
   async function load() {
     const data = await api<{ weights: WeightPoint[] }>("/api/weights");
@@ -1258,17 +1261,19 @@ function SettingsPage({ me, setMe, onFastingChange, onLogout }: { me: Me; setMe:
   const { section } = useParams();
   const navigate = useNavigate();
   const { mode: themeMode, setMode: setThemeMode } = useTheme();
-  const [profile, setProfile] = useState<Profile | null>(null);
-  const [fasting, setFasting] = useState<FastingState | null>(null);
-  const [fastingEnabledDraft, setFastingEnabledDraft] = useState(false);
-  const [reminderOffsets, setReminderOffsets] = useState<ReminderOffset[]>([0]);
+  const cachedProfile = peek<{ profile: Profile }>("/api/profile");
+  const cachedFasting = peek<FastingState>("/api/fasting");
+  const [profile, setProfile] = useState<Profile | null>(cachedProfile?.profile ?? null);
+  const [fasting, setFasting] = useState<FastingState | null>(cachedFasting);
+  const [fastingEnabledDraft, setFastingEnabledDraft] = useState(cachedFasting?.enabled ?? false);
+  const [reminderOffsets, setReminderOffsets] = useState<ReminderOffset[]>(cachedFasting?.reminderOffsets ?? [0]);
   const [autoPublish, setAutoPublish] = useState(me.user.autoPublishFoods);
   const [currentPassword, setCurrentPassword] = useState("");
   const [newPassword, setNewPassword] = useState("");
   const [confirmPassword, setConfirmPassword] = useState("");
   const [passwordStatus, setPasswordStatus] = useState("");
   const [passwordError, setPasswordError] = useState("");
-  const [health, setHealth] = useState<AppleHealthState | null>(null);
+  const [health, setHealth] = useState<AppleHealthState | null>(() => peek<AppleHealthState>("/api/apple-health"));
   const [error, setError] = useState("");
   const pwChecks = checkSignupPassword(newPassword, confirmPassword);
   const canReadHealth = me.permissions.includes("appleHealth:read");
@@ -1623,7 +1628,7 @@ function Chevron({ back = false }: { back?: boolean }) {
 
 function PermissionsPage() {
   const { t } = useI18n();
-  const [permissions, setPermissions] = useState<Record<Operation, boolean> | null>(null);
+  const [permissions, setPermissions] = useState<Record<Operation, boolean> | null>(() => peek<PermissionsResponse>("/api/rbac/permissions")?.permissions ?? null);
   const [error, setError] = useState("");
 
   useEffect(() => {
@@ -1684,7 +1689,7 @@ function FoodForm() {
   const { id } = useParams();
   const [params] = useSearchParams();
   const navigate = useNavigate();
-  const [food, setFood] = useState<Food | null>(null);
+  const [food, setFood] = useState<Food | null>(() => (id ? peek<{ food: Food }>(`/api/foods/${id}`)?.food ?? null : null));
   const [error, setError] = useState("");
   const barcode = params.get("barcode") ?? food?.barcode ?? "";
   const returnMeal = params.get("meal");
diff --git a/apps/web/src/api.ts b/apps/web/src/api.ts
index 61feb80..dcbd2f5 100644
--- a/apps/web/src/api.ts
+++ b/apps/web/src/api.ts
@@ -17,7 +17,21 @@ export function getStoredToken(): string | null {
   }
 }
 
+// Last successful GET response per path. Pages seed their state from it so
+// navigating back shows data instantly while a fresh copy loads behind it.
+const responseCache = new Map<string, unknown>();
+
+export function peek<T>(path: string): T | null {
+  return (responseCache.get(path) as T | undefined) ?? null;
+}
+
+export function clearApiCache(): void {
+  responseCache.clear();
+}
+
 export function setStoredToken(token: string | null): void {
+  // Login, logout and session expiry all change who the cached data belongs to.
+  clearApiCache();
   try {
     if (token) {
       localStorage.setItem(TOKEN_KEY, token);
@@ -51,6 +65,7 @@ export async function api<T>(path: string, init: RequestInit = {}): Promise<T> {
   if (typeof data.token === "string" && data.token.length > 0) {
     setStoredToken(data.token);
   }
+  if (!init.method || init.method.toUpperCase() === "GET") responseCache.set(path, data);
   return data as T;
 }