diff --git a/web/src/App.tsx b/web/src/App.tsx
index e739d3f..759d9f8 100644
--- a/web/src/App.tsx
+++ b/web/src/App.tsx
@@ -32,6 +32,11 @@ export function App({ dataSource }: { dataSource: DataSource }) {
       .catch((e: unknown) => setError(e instanceof Error ? e.message : String(e)));
   }, [dataSource]);
 
+  // Day presets start at the selected site's midnight, as the server's day buckets do.
+  useEffect(() => {
+    useDashboard.getState().setTimeZone(sites?.find((x) => x.id === s.siteId)?.timeZone ?? null);
+  }, [sites, s.siteId]);
+
   // Two-way sync between the URL hash and the current view / open monitor.
   useEffect(() => {
     const apply = () => useDashboard.setState(readHash(location.hash));
diff --git a/web/src/components/RangePicker.tsx b/web/src/components/RangePicker.tsx
index 2d9cb0f..e097cf4 100644
--- a/web/src/components/RangePicker.tsx
+++ b/web/src/components/RangePicker.tsx
@@ -8,12 +8,13 @@ import { Icon } from './Icon';
 export function RangePicker() {
   const preset = useDashboard((s) => s.preset);
   const custom = useDashboard((s) => s.custom);
+  const timeZone = useDashboard((s) => s.timeZone);
   const setPreset = useDashboard((s) => s.setPreset);
   const setCustom = useDashboard((s) => s.setCustom);
   const shift = useDashboard((s) => s.shift);
   const open = useDashboard((s) => s.rangeOpen);
   const setOpen = useDashboard((s) => s.setRangeOpen);
-  const range = selectRange({ preset, custom });
+  const range = selectRange({ preset, custom, timeZone });
   const [from, setFrom] = useState(toLocalInput(range.from));
   const [to, setTo] = useState(toLocalInput(range.to));
   const popRef = useRef<HTMLDivElement>(null);
diff --git a/web/src/lib/ranges.ts b/web/src/lib/ranges.ts
index 83fcf9e..e499042 100644
--- a/web/src/lib/ranges.ts
+++ b/web/src/lib/ranges.ts
@@ -1,4 +1,4 @@
-import { DAY, HOUR, MINUTE, isLiveRange } from '@pulse/core';
+import { DAY, HOUR, MINUTE, isLiveRange, startOfDay } from '@pulse/core';
 import type { Range } from '../data/source';
 
 export type PresetId = '30m' | 'today' | '24h' | '7d' | '30d' | 'custom';
@@ -27,19 +27,28 @@ export function startOfLocalDay(ts: number): number {
   return d.getTime();
 }
 
-/** Live presets end "now"; the query layer keeps the in-progress bucket for them. */
-export function presetRange(id: Exclude<PresetId, 'custom'>, now: number): Range {
+/**
+ * Live presets end "now"; the query layer keeps the in-progress bucket for them.
+ * Day presets start at midnight in `timeZone` (the site's, which the server
+ * buckets by), or in the browser's zone while the site is not known yet.
+ */
+export function presetRange(
+  id: Exclude<PresetId, 'custom'>,
+  now: number,
+  timeZone?: string | null,
+): Range {
+  const dayStart = (ts: number) => (timeZone ? startOfDay(ts, timeZone) : startOfLocalDay(ts));
   switch (id) {
     case '30m':
       return { from: now - 30 * MINUTE, to: now };
     case 'today':
-      return { from: startOfLocalDay(now), to: now };
+      return { from: dayStart(now), to: now };
     case '24h':
       return { from: now - 24 * HOUR, to: now };
     case '7d':
-      return { from: startOfLocalDay(now - 6 * DAY), to: now };
+      return { from: dayStart(now - 6 * DAY), to: now };
     case '30d':
-      return { from: startOfLocalDay(now - 29 * DAY), to: now };
+      return { from: dayStart(now - 29 * DAY), to: now };
   }
 }
 
diff --git a/web/src/pages/AnalyticsPage.tsx b/web/src/pages/AnalyticsPage.tsx
index 73fb984..44343cf 100644
--- a/web/src/pages/AnalyticsPage.tsx
+++ b/web/src/pages/AnalyticsPage.tsx
@@ -27,6 +27,7 @@ export const AnalyticsPage = forwardRef<AnalyticsPageHandle, { siteId: string }>
     const ds = useDataSource();
     const preset = useDashboard((s) => s.preset);
     const custom = useDashboard((s) => s.custom);
+    const timeZone = useDashboard((s) => s.timeZone);
     const refreshKey = useDashboard((s) => s.refreshKey);
     const metric = useDashboard((s) => s.metric);
     const setMetric = useDashboard((s) => s.setMetric);
@@ -34,8 +35,8 @@ export const AnalyticsPage = forwardRef<AnalyticsPageHandle, { siteId: string }>
     const pagesRef = useRef<BreakdownCardHandle>(null);
 
     // Presets are re-evaluated on each refresh tick, so live windows slide forward.
-    const range = selectRange({ preset, custom });
-    const key = `${siteId}|${preset}|${custom?.from}|${custom?.to}|${refreshKey}`;
+    const range = selectRange({ preset, custom, timeZone });
+    const key = `${siteId}|${preset}|${custom?.from}|${custom?.to}|${timeZone}|${refreshKey}`;
     const summary = useQuery(key, () => ds.summary(siteId, range));
     const series = useQuery(key, () => ds.timeseries(siteId, range));
     const realtime = useQuery(`${siteId}|${refreshKey}`, () => ds.realtime(siteId));
diff --git a/web/src/state/store.ts b/web/src/state/store.ts
index d34242e..ad36642 100644
--- a/web/src/state/store.ts
+++ b/web/src/state/store.ts
@@ -8,6 +8,8 @@ export type Metric = 'visitors' | 'pageviews';
 export interface DashboardState {
   view: View;
   siteId: string | null;
+  /** Time zone of the selected site; day presets start at its midnight. */
+  timeZone: string | null;
   preset: PresetId;
   /** Only meaningful when `preset === 'custom'`. */
   custom: Range | null;
@@ -22,6 +24,7 @@ export interface DashboardState {
 
   setView(view: View): void;
   setSite(siteId: string): void;
+  setTimeZone(timeZone: string | null): void;
   setPreset(preset: Exclude<PresetId, 'custom'>): void;
   setCustom(range: Range): void;
   shift(direction: -1 | 1, now?: number): void;
@@ -36,6 +39,7 @@ export interface DashboardState {
 export const useDashboard = create<DashboardState>()((set, get) => ({
   view: 'analytics',
   siteId: null,
+  timeZone: null,
   preset: '24h',
   custom: null,
   metric: 'visitors',
@@ -47,6 +51,7 @@ export const useDashboard = create<DashboardState>()((set, get) => ({
 
   setView: (view) => set({ view }),
   setSite: (siteId) => set({ siteId }),
+  setTimeZone: (timeZone) => set({ timeZone }),
   setPreset: (preset) => set({ preset, custom: null }),
   setCustom: (range) => set({ preset: 'custom', custom: range }),
   shift: (direction, now = Date.now()) => {
@@ -61,10 +66,13 @@ export const useDashboard = create<DashboardState>()((set, get) => ({
   openMonitor: (monitorId) => set({ monitorId }),
 }));
 
-export function selectRange(s: Pick<DashboardState, 'preset' | 'custom'>, now = Date.now()): Range {
+export function selectRange(
+  s: Pick<DashboardState, 'preset' | 'custom'> & Partial<Pick<DashboardState, 'timeZone'>>,
+  now = Date.now(),
+): Range {
   if (s.preset === 'custom' && s.custom) return s.custom;
   const preset = s.preset === 'custom' ? '24h' : s.preset;
-  return presetRange(preset, now);
+  return presetRange(preset, now, s.timeZone);
 }
 
 export function presetLabel(s: Pick<DashboardState, 'preset'>): string {
diff --git a/web/test/lib.test.ts b/web/test/lib.test.ts
index 5d1e895..3e3221a 100644
--- a/web/test/lib.test.ts
+++ b/web/test/lib.test.ts
@@ -50,6 +50,17 @@ describe('ranges', () => {
     expect(isLive(presetRange('7d', now), now)).toBe(true);
   });
 
+  it('starts day presets at midnight in the site time zone, not the browser one', () => {
+    expect(presetRange('today', now, 'UTC').from).toBe(Date.parse('2026-06-10T00:00:00Z'));
+    expect(presetRange('today', now, 'Asia/Kolkata').from).toBe(Date.parse('2026-06-09T18:30:00Z'));
+    expect(presetRange('7d', now, 'America/New_York').from).toBe(
+      Date.parse('2026-06-04T04:00:00Z'),
+    );
+    expect(selectRange({ preset: 'today', custom: null, timeZone: 'Asia/Kolkata' }, now).from).toBe(
+      Date.parse('2026-06-09T18:30:00Z'),
+    );
+  });
+
   it('shifts windows without leaving the retained history', () => {
     const r = { from: now - 2 * HOUR, to: now };
     expect(shiftRange(r, -1, now)).toEqual({ from: now - 4 * HOUR, to: now - 2 * HOUR });