diff --git a/docs/api/openapi.yaml b/docs/api/openapi.yaml
index 734d96df3..3d0288869 100644
--- a/docs/api/openapi.yaml
+++ b/docs/api/openapi.yaml
@@ -26856,7 +26856,7 @@ components:
             - ko
         today:
           description: "Optional override of the reference date used to resolve relative phrases (\"tomorrow\", \"next Monday\").
-            Format: `YYYY-MM-DD`. Defaults to the server's UTC day."
+            Format: `YYYY-MM-DD`. Defaults to the account's own day in its time zone."
           type: string
           pattern: ^\d{4}-\d{2}-\d{2}$
       required:
diff --git a/messages/de.json b/messages/de.json
index b370a245b..c34ec8463 100644
--- a/messages/de.json
+++ b/messages/de.json
@@ -2843,7 +2843,7 @@
     "coach": {
       "refusalOutOfScope": "Ich kann nur bei den Gesundheitsdaten in deinem Log helfen: Messwerte, Medikamente, Stimmung, Trends. Fragen außerhalb dieses Themas beantworte ich nicht.",
       "refusalInjection": "In deiner Nachricht stehen Anweisungen, die meine Vorgaben überschreiben sollen. Ich bin der HealthLog-Coach und fasse ausschließlich deine eigenen Gesundheitsdaten zusammen. Formuliere deine Frage bitte in diesem Rahmen neu.",
-      "errorBudget": "Du hast das heutige Coach-Limit erreicht. Das Budget setzt sich um Mitternacht (UTC) zurück.",
+      "errorBudget": "Du hast das heutige Coach-Limit erreicht. Das Budget setzt sich um Mitternacht in deiner Zeitzone zurück.",
       "errorProvider": "Der Coach konnte gerade keinen Auswertungs-Anbieter erreichen. Bitte versuche es in einem Moment erneut.",
       "errorDemo": "In der Demo antwortet der Coach nicht.",
       "errorNoProvider": "Der Coach liest deine erfassten Gesundheitsdaten und beantwortet Fragen dazu (keine medizinische Beratung). Dafür braucht HealthLog einen KI-Anbieter. Verbinde deinen eigenen Schlüssel oder ein lokales Modell.",
@@ -2999,7 +2999,7 @@
       "settingsSaved": "Gespeichert",
       "settingsCancel": "Abbrechen",
       "dailyLimitTitle": "Heute-Limit erreicht",
-      "dailyLimitBody": "Tageslimit erreicht. Das Budget setzt sich um Mitternacht (UTC) zurück.",
+      "dailyLimitBody": "Tageslimit erreicht. Das Budget setzt sich um Mitternacht in deiner Zeitzone zurück.",
       "providerRateLimitTitle": "Provider rate-limited",
       "providerRateLimitBody": "Provider ist temporär überlastet; Reset in ~5 min.",
       "cluster": {
diff --git a/messages/en.json b/messages/en.json
index 232132002..fd91f3c6d 100644
--- a/messages/en.json
+++ b/messages/en.json
@@ -2843,7 +2843,7 @@
     "coach": {
       "refusalOutOfScope": "I can only help with the health metrics in your log: measurements, medications, mood, trends. I cannot answer questions outside that scope.",
       "refusalInjection": "I noticed wording that tries to override my instructions. I am the HealthLog Coach and only summarise your own health data. Please rephrase your question in those terms.",
-      "errorBudget": "You've reached today's Coach usage limit. The budget refreshes at midnight UTC.",
+      "errorBudget": "You've reached today's Coach usage limit. The budget refreshes at midnight in your time zone.",
       "errorProvider": "The Coach could not reach an Insights provider just now. Please try again in a moment.",
       "errorDemo": "The Coach doesn't answer in the demo.",
       "errorNoProvider": "The Coach reads your logged health data and answers questions about it (not medical advice). HealthLog needs an AI provider for that. Connect your own key or a local model.",
@@ -2999,7 +2999,7 @@
       "settingsSaved": "Saved",
       "settingsCancel": "Cancel",
       "dailyLimitTitle": "Daily limit reached",
-      "dailyLimitBody": "Daily limit reached. The budget refreshes at midnight UTC.",
+      "dailyLimitBody": "Daily limit reached. The budget refreshes at midnight in your time zone.",
       "providerRateLimitTitle": "Provider rate-limited",
       "providerRateLimitBody": "Provider temporarily rate-limited; retry in ~5 min.",
       "cluster": {
diff --git a/messages/es.json b/messages/es.json
index 521e07378..487a61a25 100644
--- a/messages/es.json
+++ b/messages/es.json
@@ -2843,7 +2843,7 @@
     "coach": {
       "refusalOutOfScope": "Solo puedo ayudarte con los datos de salud de tu registro: mediciones, medicamentos, estado de ánimo, tendencias. Preguntas fuera de ese ámbito no las respondo.",
       "refusalInjection": "Tu mensaje contiene instrucciones que pretenden sobrescribir mis indicaciones. Soy el coach de HealthLog y solo resumo tus propios datos de salud. Reformula tu pregunta dentro de ese marco.",
-      "errorBudget": "Has alcanzado el límite diario del coach. El cupo se reinicia a medianoche (UTC).",
+      "errorBudget": "Has alcanzado el límite diario del coach. El cupo se reinicia a medianoche en tu zona horaria.",
       "errorProvider": "El coach no ha podido contactar con un proveedor de análisis ahora mismo. Inténtalo en un momento.",
       "errorDemo": "En la demo, el Coach no responde.",
       "errorNoProvider": "El coach lee tus datos de salud registrados y responde preguntas sobre ellos (no es consejo médico). HealthLog necesita un proveedor de IA para ello: conecta tu propia clave o un modelo local.",
@@ -2999,7 +2999,7 @@
       "settingsSaved": "Guardado",
       "settingsCancel": "Cancelar",
       "dailyLimitTitle": "Límite diario alcanzado",
-      "dailyLimitBody": "Límite diario alcanzado. El cupo se reinicia a medianoche (UTC).",
+      "dailyLimitBody": "Límite diario alcanzado. El cupo se reinicia a medianoche en tu zona horaria.",
       "providerRateLimitTitle": "Proveedor con límite de tasa",
       "providerRateLimitBody": "El proveedor está temporalmente saturado; reinicio en ~5 min.",
       "cluster": {
diff --git a/messages/fr.json b/messages/fr.json
index c20ce3479..87d13f4fb 100644
--- a/messages/fr.json
+++ b/messages/fr.json
@@ -2843,7 +2843,7 @@
     "coach": {
       "refusalOutOfScope": "Je ne peux aider que pour les données de santé de ton journal : mesures, médicaments, humeur, tendances. Les questions hors de ce périmètre ne sont pas traitées.",
       "refusalInjection": "Ton message contient des instructions qui cherchent à remplacer mes consignes. Je suis le coach HealthLog et je ne résume que tes propres données de santé. Reformule ta question dans ce cadre.",
-      "errorBudget": "Tu as atteint la limite quotidienne du coach. Le quota se réinitialise à minuit (UTC).",
+      "errorBudget": "Tu as atteint la limite quotidienne du coach. Le quota se réinitialise à minuit dans ton fuseau horaire.",
       "errorProvider": "Le coach n’a pas pu joindre un fournisseur d’analyse maintenant. Réessaie dans un instant.",
       "errorDemo": "Dans la démo, le Coach ne répond pas.",
       "errorNoProvider": "Le coach lit tes données de santé enregistrées et répond aux questions à leur sujet (pas un avis médical). HealthLog a besoin d'un fournisseur d'IA pour cela : connecte ta propre clé ou un modèle local.",
@@ -2999,7 +2999,7 @@
       "settingsSaved": "Enregistré",
       "settingsCancel": "Annuler",
       "dailyLimitTitle": "Limite quotidienne atteinte",
-      "dailyLimitBody": "Limite quotidienne atteinte. Le quota se réinitialise à minuit (UTC).",
+      "dailyLimitBody": "Limite quotidienne atteinte. Le quota se réinitialise à minuit dans ton fuseau horaire.",
       "providerRateLimitTitle": "Fournisseur limité en débit",
       "providerRateLimitBody": "Le fournisseur est temporairement saturé ; réinitialisation dans ~5 min.",
       "cluster": {
diff --git a/messages/it.json b/messages/it.json
index 292b56dd7..01f51b19d 100644
--- a/messages/it.json
+++ b/messages/it.json
@@ -2843,7 +2843,7 @@
     "coach": {
       "refusalOutOfScope": "Posso aiutarti solo con i dati di salute del tuo log: misurazioni, farmaci, umore, trend. Domande fuori da questo ambito non le rispondo.",
       "refusalInjection": "Nel tuo messaggio ci sono istruzioni che cercano di sovrascrivere le mie indicazioni. Sono il coach di HealthLog e riassumo solo i tuoi dati di salute: riformula la domanda in questo perimetro.",
-      "errorBudget": "Hai raggiunto il limite giornaliero del coach. Il budget si reimposta a mezzanotte (UTC).",
+      "errorBudget": "Hai raggiunto il limite giornaliero del coach. Il budget si reimposta a mezzanotte nel tuo fuso orario.",
       "errorProvider": "Il coach non è riuscito a contattare un provider di analisi ora. Riprova fra poco.",
       "errorDemo": "Nella demo il Coach non risponde.",
       "errorNoProvider": "Il coach legge i tuoi dati di salute registrati e risponde a domande su di essi (non è consulenza medica). HealthLog ha bisogno di un provider IA per questo: collega la tua chiave o un modello locale.",
@@ -2999,7 +2999,7 @@
       "settingsSaved": "Salvato",
       "settingsCancel": "Annulla",
       "dailyLimitTitle": "Limite giornaliero raggiunto",
-      "dailyLimitBody": "Limite giornaliero raggiunto. Il budget si reimposta a mezzanotte (UTC).",
+      "dailyLimitBody": "Limite giornaliero raggiunto. Il budget si reimposta a mezzanotte nel tuo fuso orario.",
       "providerRateLimitTitle": "Provider con rate-limit",
       "providerRateLimitBody": "Il provider è temporaneamente sovraccarico; reset in ~5 min.",
       "cluster": {
diff --git a/messages/ko.json b/messages/ko.json
index db3908b97..f8d8ad8e6 100644
--- a/messages/ko.json
+++ b/messages/ko.json
@@ -2843,7 +2843,7 @@
     "coach": {
       "refusalOutOfScope": "기록에 있는 건강 지표(측정값, 약, 기분, 추이)만 도와드릴 수 있어요. 그 밖의 질문에는 답할 수 없어요.",
       "refusalInjection": "제 지시를 덮어쓰려는 표현이 보였어요. 저는 HealthLog 코치이고 회원님의 건강 데이터만 정리해 드려요. 그 범위로 질문을 다시 적어 주세요.",
-      "errorBudget": "오늘 코치 사용 한도에 도달했어요. 사용량은 UTC 자정에 초기화돼요.",
+      "errorBudget": "오늘 코치 사용 한도에 도달했어요. 사용량은 내 시간대의 자정에 초기화돼요.",
       "errorProvider": "지금은 코치가 인사이트 제공자에 연결하지 못했어요. 잠시 후 다시 시도해 주세요.",
       "errorDemo": "데모에서는 코치가 답하지 않아요.",
       "errorNoProvider": "코치는 기록된 건강 데이터를 읽고 그에 대한 질문에 답해요(의학적 조언은 아니에요). 그러려면 HealthLog에 AI 제공자가 필요해요. 직접 발급한 키나 로컬 모델을 연결해 주세요.",
@@ -2999,7 +2999,7 @@
       "settingsSaved": "저장됨",
       "settingsCancel": "취소",
       "dailyLimitTitle": "하루 한도 도달",
-      "dailyLimitBody": "하루 한도에 도달했어요. 사용량은 UTC 자정에 초기화돼요.",
+      "dailyLimitBody": "하루 한도에 도달했어요. 사용량은 내 시간대의 자정에 초기화돼요.",
       "providerRateLimitTitle": "제공자 요청 제한",
       "providerRateLimitBody": "제공자가 일시적으로 요청을 제한하고 있어요. 5분쯤 뒤에 다시 시도해 주세요.",
       "cluster": {
diff --git a/messages/pl.json b/messages/pl.json
index dba9b65ea..602f5a443 100644
--- a/messages/pl.json
+++ b/messages/pl.json
@@ -2843,7 +2843,7 @@
     "coach": {
       "refusalOutOfScope": "Mogę pomóc tylko w sprawach danych zdrowotnych z twojego logu: pomiarów, leków, nastroju, trendów. Pytań spoza tego zakresu nie podejmuję.",
       "refusalInjection": "Twoja wiadomość zawiera instrukcje, które próbują nadpisać moje wytyczne. Jestem coachem HealthLog i podsumowuję wyłącznie twoje własne dane zdrowotne. Przeformułuj pytanie w tych ramach.",
-      "errorBudget": "Osiągnięto dzienny limit coacha. Limit resetuje się o północy (UTC).",
+      "errorBudget": "Osiągnięto dzienny limit coacha. Limit resetuje się o północy w Twojej strefie czasowej.",
       "errorProvider": "Coach nie mógł teraz skontaktować się z dostawcą analizy. Spróbuj za chwilę.",
       "errorDemo": "W wersji demo Coach nie odpowiada.",
       "errorNoProvider": "Coach czyta Twoje zapisane dane zdrowotne i odpowiada na pytania o nie (to nie porada medyczna). HealthLog potrzebuje do tego dostawcy AI: połącz własny klucz lub model lokalny.",
@@ -2999,7 +2999,7 @@
       "settingsSaved": "Zapisano",
       "settingsCancel": "Anuluj",
       "dailyLimitTitle": "Osiągnięto dzienny limit",
-      "dailyLimitBody": "Osiągnięto dzienny limit. Limit resetuje się o północy (UTC).",
+      "dailyLimitBody": "Osiągnięto dzienny limit. Limit resetuje się o północy w Twojej strefie czasowej.",
       "providerRateLimitTitle": "Dostawca z ograniczeniem",
       "providerRateLimitBody": "Dostawca jest tymczasowo przeciążony; reset za ~5 min.",
       "cluster": {
diff --git a/src/app/api/admin/provider-health/route.ts b/src/app/api/admin/provider-health/route.ts
index 199d99923..bfe9eeffd 100644
--- a/src/app/api/admin/provider-health/route.ts
+++ b/src/app/api/admin/provider-health/route.ts
@@ -73,11 +73,13 @@ interface ProviderHealthSummary {
 const CENTRAL_TYPES = [...OPERATOR_HELD_PROVIDER_TYPES];
 
 export const GET = apiHandler(async () => {
-  await requireAdmin();
+  const { user } = await requireAdmin();
   annotate({ action: { name: "admin.provider-health.get" } });
 
-  // The UTC day the ledger buckets by — the same key every reservation writes.
-  const dateKey = buildDateKey();
+  // The ledger buckets each account by its own local day; the operator's
+  // "today" is the day in the operator's own zone, which on a single-zone
+  // instance is everyone's.
+  const dateKey = await buildDateKey(user.id);
 
   const groups = await prisma.providerHealth.groupBy({
     // `lastStatus` joins the grouping key rather than an aggregate: the
diff --git a/src/app/api/ai/test/route.ts b/src/app/api/ai/test/route.ts
index eb8166511..1a1e25402 100644
--- a/src/app/api/ai/test/route.ts
+++ b/src/app/api/ai/test/route.ts
@@ -145,7 +145,7 @@ export const POST = apiHandler(async (request: NextRequest) => {
   // `admin-key` is the operator's own credential and draws the operator
   // ceiling; an override names the caller's own key, and every other resolved
   // type is the user's own egress, so those draw the user-plan ceiling.
-  const dateKey = buildDateKey();
+  const dateKey = await buildDateKey(user.id);
   const reservation = await reserveBudget(
     user.id,
     AI_TEST_MAX_TOKENS,
diff --git a/src/app/api/documents/inbound/[id]/extract/route.ts b/src/app/api/documents/inbound/[id]/extract/route.ts
index 1fc8338c5..e011909a8 100644
--- a/src/app/api/documents/inbound/[id]/extract/route.ts
+++ b/src/app/api/documents/inbound/[id]/extract/route.ts
@@ -183,7 +183,7 @@ async function reserveFor(
   providerType: ProviderChainType,
   tokens: number,
 ): Promise<AiRunBudget | null> {
-  const dateKey = buildDateKey();
+  const dateKey = await buildDateKey(userId);
   const reservation = await reserveBudget(
     userId,
     tokens,
diff --git a/src/app/api/documents/inbound/[id]/index/route.ts b/src/app/api/documents/inbound/[id]/index/route.ts
index 7c01083fc..514c266ba 100644
--- a/src/app/api/documents/inbound/[id]/index/route.ts
+++ b/src/app/api/documents/inbound/[id]/index/route.ts
@@ -200,7 +200,7 @@ async function handleVisionIndex(
   const rl = await checkDocumentAiRateLimit(userId);
   if (!rl.allowed) return documentAiRateLimited(rl);
 
-  const dateKey = buildDateKey();
+  const dateKey = await buildDateKey(userId);
   const reservation = await reserveBudget(
     userId,
     DOCUMENT_INDEX_RESERVE_TOKENS,
diff --git a/src/app/api/documents/inbound/[id]/suggest/route.ts b/src/app/api/documents/inbound/[id]/suggest/route.ts
index 28ac50c64..da9d78fcc 100644
--- a/src/app/api/documents/inbound/[id]/suggest/route.ts
+++ b/src/app/api/documents/inbound/[id]/suggest/route.ts
@@ -122,7 +122,7 @@ async function reserveFor(
   userId: string,
   providerType: ProviderChainType,
 ): Promise<AiRunBudget | null> {
-  const dateKey = buildDateKey();
+  const dateKey = await buildDateKey(userId);
   const reservation = await reserveBudget(
     userId,
     AI_BUDGETS.documentAssist.maxTokens,
diff --git a/src/app/api/documents/inbound/[id]/summary/route.ts b/src/app/api/documents/inbound/[id]/summary/route.ts
index 9c2c7c484..c5e293890 100644
--- a/src/app/api/documents/inbound/[id]/summary/route.ts
+++ b/src/app/api/documents/inbound/[id]/summary/route.ts
@@ -216,7 +216,7 @@ async function reserveFor(
   ask: SummaryRequest,
   providerType: ProviderChainType,
 ): Promise<AiRunBudget | null> {
-  const dateKey = buildDateKey();
+  const dateKey = await buildDateKey(ask.userId);
   const reservation = await reserveBudget(
     ask.userId,
     budgetFor(ask.mode),
diff --git a/src/app/api/labs/ocr/extract/route.ts b/src/app/api/labs/ocr/extract/route.ts
index 94a76ee03..a4e21e9d2 100644
--- a/src/app/api/labs/ocr/extract/route.ts
+++ b/src/app/api/labs/ocr/extract/route.ts
@@ -157,7 +157,7 @@ async function handleTextExtract(
   // v1.21.0 (F1) — the operator-cost cap applies only when the picked provider
   // egresses on the operator's own key; a BYOK / Codex / local pick runs on the
   // user's own plan and gets the generous user-plan ceiling.
-  const dateKey = buildDateKey();
+  const dateKey = await buildDateKey(userId);
   const reservation = await reserveBudget(
     userId,
     OCR_RESERVE_TOKENS.text,
@@ -218,7 +218,7 @@ async function handleVisionExtract(
   // v1.21.0 (F1) — the operator-cost cap applies only when the picked vision
   // provider egresses on the operator's own key; a BYOK / Codex pick runs on
   // the user's own plan and gets the generous user-plan ceiling.
-  const dateKey = buildDateKey();
+  const dateKey = await buildDateKey(userId);
   const reservation = await reserveBudget(
     userId,
     OCR_RESERVE_TOKENS.vision,
diff --git a/src/app/api/medications/extract/route.ts b/src/app/api/medications/extract/route.ts
index c8bee510e..aaf949bfb 100644
--- a/src/app/api/medications/extract/route.ts
+++ b/src/app/api/medications/extract/route.ts
@@ -225,7 +225,10 @@ async function handleExtract(request: NextRequest): Promise<Response> {
     chain.map((entry) => entry.providerType),
   );
 
-  const today = todayOverride ?? buildDateKey();
+  // The account's own today: "tomorrow" in a description means the
+  // person's tomorrow, and the same key is the budget day below.
+  const accountToday = await buildDateKey(userId);
+  const today = todayOverride ?? accountToday;
   const { systemPrompt, userPrompt } = buildMedicationExtractionPrompt({
     text,
     today,
@@ -239,7 +242,7 @@ async function handleExtract(request: NextRequest): Promise<Response> {
   // paying for their own key by the operator's ceiling. `resolveDailyCap`
   // charges the operator ceiling only when the chain's primary is the
   // operator's own credential; every other chain gets the user-plan ceiling.
-  const dateKey = buildDateKey();
+  const dateKey = accountToday;
   const estimatedTokens =
     MAX_OUTPUT_TOKENS +
     Math.ceil((systemPrompt.length + userPrompt.length) / 4);
diff --git a/src/components/insights/coach-panel/chat-bubble.tsx b/src/components/insights/coach-panel/chat-bubble.tsx
index 9a712d453..dbd8738b2 100644
--- a/src/components/insights/coach-panel/chat-bubble.tsx
+++ b/src/components/insights/coach-panel/chat-bubble.tsx
@@ -560,7 +560,7 @@ function ChatBubbleImpl({
 
   // v1.4.25 W5 — map server-emitted error codes to specific Coach
   // i18n keys. Distinct user-quota and provider-rate-limit copy so the
-  // user understands daily-cap (resets at UTC midnight) vs. transient
+  // user understands daily-cap (resets at their local midnight) vs. transient
   // provider load (retry in ~5 min). Codes that have no dedicated
   // translation fall back to the generic provider-unavailable copy.
   const errorKey = errorCode ? errorCodeToI18nKey(errorCode) : null;
diff --git a/src/lib/ai/coach/__tests__/budget.test.ts b/src/lib/ai/coach/__tests__/budget.test.ts
index 3757daa61..aea8edaa7 100644
--- a/src/lib/ai/coach/__tests__/budget.test.ts
+++ b/src/lib/ai/coach/__tests__/budget.test.ts
@@ -22,16 +22,45 @@ vi.mock("@/lib/db", () => ({
   },
 }));
 
+const { zoneOf } = vi.hoisted(() => ({
+  zoneOf: vi.fn(async (userId: string) =>
+    userId === "berlin"
+      ? "Europe/Berlin"
+      : userId === "new-york"
+        ? "America/New_York"
+        : "UTC",
+  ),
+}));
+vi.mock("@/lib/tz/resolver", () => ({ resolveUserTimezone: zoneOf }));
+
+/**
+ * The budget day turns at the account's own midnight, the boundary the daily
+ * briefing and the other per-day generations use. On the UTC day, the first
+ * generations of a new local day east of UTC were counted against the old
+ * day's exhausted ceiling.
+ */
 describe("buildDateKey", () => {
-  it("formats UTC YYYY-MM-DD", () => {
-    // 2026-05-10T22:30Z is UTC May 10 — Berlin would be May 11 already
-    const key = buildDateKey(new Date("2026-05-10T22:30:00.000Z"));
-    expect(key).toBe("2026-05-10");
+  it("is the account's local day, not the UTC day", async () => {
+    // 22:30 UTC on May 10 is already 00:30 on May 11 in Berlin (CEST).
+    const at = new Date("2026-05-10T22:30:00.000Z");
+    await expect(buildDateKey("berlin", at)).resolves.toBe("2026-05-11");
+    await expect(buildDateKey("utc", at)).resolves.toBe("2026-05-10");
+    expect(zoneOf).toHaveBeenCalledWith("berlin");
   });
 
-  it("rolls forward at UTC midnight", () => {
-    const key = buildDateKey(new Date("2026-05-11T00:01:00.000Z"));
-    expect(key).toBe("2026-05-11");
+  it("turns at local midnight on either side of it", async () => {
+    // Berlin: 23:59 local on May 10, then 00:01 local on May 11.
+    await expect(
+      buildDateKey("berlin", new Date("2026-05-10T21:59:00.000Z")),
+    ).resolves.toBe("2026-05-10");
+    await expect(
+      buildDateKey("berlin", new Date("2026-05-10T22:01:00.000Z")),
+    ).resolves.toBe("2026-05-11");
+    // West of UTC the local day ends after the UTC one: 02:00 UTC on May 11
+    // is still the evening of May 10 in New York.
+    await expect(
+      buildDateKey("new-york", new Date("2026-05-11T02:00:00.000Z")),
+    ).resolves.toBe("2026-05-10");
   });
 });
 
diff --git a/src/lib/ai/coach/budget.ts b/src/lib/ai/coach/budget.ts
index f1d387e0a..2849190b2 100644
--- a/src/lib/ai/coach/budget.ts
+++ b/src/lib/ai/coach/budget.ts
@@ -9,12 +9,13 @@
  *     us add per-day analytics ("avg replies per active user") later
  *     without further migrations.
  *
- * `dateKey` is a UTC `YYYY-MM-DD` string. UTC, not Europe/Berlin: the
- * job runner that may seed off-hour tasks (planned v1.5) needs a
- * boundary that does not jump on DST. Display layers can format with
- * the user's timezone.
+ * `dateKey` is a `YYYY-MM-DD` string: the calendar day in the account's own
+ * time zone (`buildDateKey`), the same boundary as the daily briefing and
+ * every other per-day surface.
  */
 import { prisma } from "@/lib/db";
+import { userDayKey } from "@/lib/tz/format";
+import { resolveUserTimezone } from "@/lib/tz/resolver";
 import type { ProviderChainType } from "@/lib/ai/provider-chain";
 
 /**
@@ -215,8 +216,9 @@ export interface DailySpend {
 
 export async function readDailySpend(
   userId: string,
-  dateKey: string = buildDateKey(),
+  dateKey?: string,
 ): Promise<DailySpend> {
+  dateKey ??= await buildDateKey(userId);
   const row = await prisma.coachUsage.findUnique({
     where: { userId_dateKey: { userId, dateKey } },
     select: { totalTokens: true, operatorTokens: true },
@@ -228,15 +230,24 @@ export async function readDailySpend(
 }
 
 /**
- * Build the UTC day-key for a given clock. Defaults to "now".
+ * The budget day of one account at `at` (default now): the calendar day in
+ * the account's own time zone.
  *
- * UTC choice: the budget guards spend against the operator's LLM
- * bill — the bill cycles at the provider's UTC midnight, so aligning
- * the local meter to the same boundary keeps reasoning trivial.
+ * Up to v1.42.1 this was the UTC day. The daily briefing and the other
+ * per-day generations run on the account's local day, so in a zone east of
+ * UTC the first ones of a new local day still counted against the old UTC
+ * day, whose ceiling the evening had used up: a burst of refusals right
+ * after local midnight. The day now turns where the person's day turns.
+ *
+ * A caller resolves the key once per request or job and hands the same key
+ * to the reservation and the reconcile, so both land on one row even when
+ * the call spans midnight.
  */
-export function buildDateKey(at: Date = new Date()): string {
-  // eslint-disable-next-line healthlog/no-utc-day-key -- UTC by design: the spend meter follows the provider's UTC billing day (see the doc comment)
-  return at.toISOString().slice(0, 10);
+export async function buildDateKey(
+  userId: string,
+  at: Date = new Date(),
+): Promise<string> {
+  return userDayKey(at, await resolveUserTimezone(userId));
 }
 
 /**
diff --git a/src/lib/ai/coach/self-context-questions.ts b/src/lib/ai/coach/self-context-questions.ts
index 86d352c7d..ac0959832 100644
--- a/src/lib/ai/coach/self-context-questions.ts
+++ b/src/lib/ai/coach/self-context-questions.ts
@@ -240,7 +240,7 @@ export async function deriveClarifyingQuestions(
     // serialises them on the row's unique key instead. The cap follows the
     // chain's cost owner, so a user on their own plan is not held to the
     // operator-cost ceiling.
-    const dateKey = buildDateKey();
+    const dateKey = await buildDateKey(userId);
     const reservation = await reserveBudget(
       userId,
       QUESTIONS_MAX_TOKENS,
diff --git a/src/lib/ai/coach/turn/budget.ts b/src/lib/ai/coach/turn/budget.ts
index 85a78cc69..603a08019 100644
--- a/src/lib/ai/coach/turn/budget.ts
+++ b/src/lib/ai/coach/turn/budget.ts
@@ -68,7 +68,7 @@ export async function reserveTurnBudget(args: {
   // egresses through the operator's own key or account; a chain on the
   // person's own plan or key gets the generous user-plan ceiling.
   const dailyCap = resolveDailyCap(chain);
-  const reqDateKey = buildDateKey();
+  const reqDateKey = await buildDateKey(userId);
   const firstRound = toolMode
     ? Math.max(1, Math.floor(args.firstRound ?? AI_BUDGETS.coach.maxTokens))
     : AI_BUDGETS.coach.maxTokens;
diff --git a/src/lib/documents/auto-stage-labs.ts b/src/lib/documents/auto-stage-labs.ts
index ef9133ee8..fc694a56e 100644
--- a/src/lib/documents/auto-stage-labs.ts
+++ b/src/lib/documents/auto-stage-labs.ts
@@ -290,7 +290,7 @@ export async function maybeAutoStageLabFacts(
   // ceiling under the cost owner the auto-index resolved.
   // v1.38.19 — auto-staging runs off the upload, with no one waiting
   // on it: a background surface, so half the day's ceiling.
-  const dateKey = buildDateKey();
+  const dateKey = await buildDateKey(userId);
   const reservation = await reserveBudget(
     userId,
     AI_BUDGETS.ocrExtractText.maxTokens,
diff --git a/src/lib/documents/fenced-chat.ts b/src/lib/documents/fenced-chat.ts
index 1af3eb30a..90a834650 100644
--- a/src/lib/documents/fenced-chat.ts
+++ b/src/lib/documents/fenced-chat.ts
@@ -312,7 +312,7 @@ export async function streamFencedReply(
   await appendMessage({ conversationId, role: "user", content: message });
 
   // ── Budget reservation (atomic, before the provider call) ──
-  const dateKey = buildDateKey();
+  const dateKey = await buildDateKey(userId);
   const reservation = await reserveBudget(
     userId,
     AI_BUDGETS.documentChat.maxTokens,
diff --git a/src/lib/documents/index-document.ts b/src/lib/documents/index-document.ts
index 9674b2e1d..80c3ff25d 100644
--- a/src/lib/documents/index-document.ts
+++ b/src/lib/documents/index-document.ts
@@ -242,7 +242,7 @@ async function tryProviderIndex(
     return { outcome: null, note: null };
   }
 
-  const dateKey = buildDateKey();
+  const dateKey = await buildDateKey(userId);
   const reservation = await reserveBudget(
     userId,
     AI_BUDGETS.documentTranscribe.maxTokens,
diff --git a/src/lib/insights/briefing-provider.ts b/src/lib/insights/briefing-provider.ts
index fb2686927..422ec7fbc 100644
--- a/src/lib/insights/briefing-provider.ts
+++ b/src/lib/insights/briefing-provider.ts
@@ -93,7 +93,7 @@ export interface RunBriefingCompletionArgs {
    * a pinned seed would reproduce the phrasing the re-roll exists to vary.
    */
   seed?: number;
-  /** UTC day-key override; defaults to today. Tests pin it. */
+  /** Budget day-key override; defaults to the account's today. Tests pin it. */
   dateKey?: string;
   /**
    * v1.41 — `daily_briefing` on the calls that may reason (the generation and
@@ -122,7 +122,7 @@ export interface RunBriefingCompletionArgs {
 export async function runBriefingCompletion(
   args: RunBriefingCompletionArgs,
 ): Promise<RunRawWithFallbackResult> {
-  const dateKey = args.dateKey ?? buildDateKey();
+  const dateKey = args.dateKey ?? (await buildDateKey(args.userId));
 
   // v1.41 — one resolution per call: the operator's switch and cap, the payer
   // from the chain's primary. `undefined` is today's wire.
diff --git a/src/lib/insights/status-provider.ts b/src/lib/insights/status-provider.ts
index d098fe15c..6646c9771 100644
--- a/src/lib/insights/status-provider.ts
+++ b/src/lib/insights/status-provider.ts
@@ -250,7 +250,7 @@ export async function runStatusCompletion(
   // credential (`admin-openai` / `admin-codex`). A self-hoster on their own key
   // or a local model is measured against the generous user-plan ceiling, so
   // their own hardware/plan is never rationed by the operator's bill.
-  const dateKey = buildDateKey();
+  const dateKey = await buildDateKey(userId);
   // Thinking is billed as output, so a reasoning call reserves its thinking
   // budget too; the reconcile below settles on the reported count.
   const estimatedTokens =
diff --git a/src/lib/jobs/coach-nudge-ai.ts b/src/lib/jobs/coach-nudge-ai.ts
index 3df90feeb..4ffb0e27e 100644
--- a/src/lib/jobs/coach-nudge-ai.ts
+++ b/src/lib/jobs/coach-nudge-ai.ts
@@ -211,7 +211,7 @@ export const composeNudgeWithAI: ComposeNudgeWithAI = async (params) => {
     const maxTokens = budget.maxTokens ?? 160;
     // v1.38.19 — a background surface: half the day's ceiling.
     const dailyCap = resolveDailyCapFor("job", chain);
-    const dateKey = buildDateKey();
+    const dateKey = await buildDateKey(params.userId);
 
     // Per-user budget gate (atomic reserve; refunds itself on refusal).
     const reservation = await reserveBudget(
diff --git a/src/lib/jobs/document-content-index-backfill.ts b/src/lib/jobs/document-content-index-backfill.ts
index 357619313..f355cb7d3 100644
--- a/src/lib/jobs/document-content-index-backfill.ts
+++ b/src/lib/jobs/document-content-index-backfill.ts
@@ -268,7 +268,7 @@ export async function runContentIndexBackfillForUser(
         break outer;
       }
 
-      const dateKey = buildDateKey();
+      const dateKey = await buildDateKey(userId);
       const reservation = await reserveBudget(
         userId,
         AI_BUDGETS.documentTranscribe.maxTokens,
diff --git a/src/lib/jobs/document-summary.ts b/src/lib/jobs/document-summary.ts
index 02f495b81..de889748f 100644
--- a/src/lib/jobs/document-summary.ts
+++ b/src/lib/jobs/document-summary.ts
@@ -223,7 +223,7 @@ export async function runDocumentSummaryJob(
     return;
   }
 
-  const dateKey = buildDateKey();
+  const dateKey = await buildDateKey(userId);
   const reservation = await reserveBudget(
     userId,
     AI_BUDGETS.documentSummary.maxTokens,
diff --git a/src/lib/jobs/reaction-line.ts b/src/lib/jobs/reaction-line.ts
index a30e48d3b..1051aae19 100644
--- a/src/lib/jobs/reaction-line.ts
+++ b/src/lib/jobs/reaction-line.ts
@@ -592,7 +592,7 @@ export async function runReactionLine(
         generationClaimId,
         job.userId,
         revision,
-        buildDateKey(),
+        await buildDateKey(job.userId),
         // v1.38.19 — a background surface: half the day's ceiling.
         resolveDailyCapFor("job", chain),
         resolveCostOwner(chain),
diff --git a/src/lib/openapi/routes/medications/schemas.ts b/src/lib/openapi/routes/medications/schemas.ts
index 83d8de485..8f6bce5d3 100644
--- a/src/lib/openapi/routes/medications/schemas.ts
+++ b/src/lib/openapi/routes/medications/schemas.ts
@@ -1036,7 +1036,7 @@ export const medicationExtractRequest = z
       .regex(/^\d{4}-\d{2}-\d{2}$/)
       .optional()
       .describe(
-        'Optional override of the reference date used to resolve relative phrases ("tomorrow", "next Monday"). Format: `YYYY-MM-DD`. Defaults to the server\'s UTC day.',
+        'Optional override of the reference date used to resolve relative phrases ("tomorrow", "next Monday"). Format: `YYYY-MM-DD`. Defaults to the account\'s own day in its time zone.',
       ),
   })
   .meta({
diff --git a/tests/integration/coach-budget-reservation.test.ts b/tests/integration/coach-budget-reservation.test.ts
index 2b4f28443..0ddc28a1d 100644
--- a/tests/integration/coach-budget-reservation.test.ts
+++ b/tests/integration/coach-budget-reservation.test.ts
@@ -9,7 +9,7 @@
  * prove both contracts against a real Postgres; a mocked client could not
  * detect a missing atomic increment.
  */
-import { beforeEach, describe, expect, it } from "vitest";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 
 import { getPrismaClient, truncateAllTables } from "./setup";
 
@@ -180,3 +180,64 @@ describe("reserveBudget (real Postgres)", () => {
     expect(row?.totalTokens).toBeGreaterThan(0);
   });
 });
+
+/**
+ * The budget day turns at the account's own midnight, the boundary the daily
+ * briefing uses. On the UTC day a Berlin account's first generations after
+ * local midnight still counted against the previous day's spent ceiling.
+ */
+describe("the budget day is the account's local day", () => {
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it("opens a fresh day at local midnight while the UTC day is still running", async () => {
+    const { buildDateKey, reserveBudget } =
+      await import("@/lib/ai/coach/budget");
+    const user = await getPrismaClient().user.create({
+      data: {
+        username: "budget-berlin",
+        email: "budget-berlin@example.test",
+        role: "USER",
+        timezone: "Europe/Berlin",
+      },
+    });
+    // 22:30 UTC on 2026-06-19 is 00:30 on 2026-06-20 in Berlin (CEST).
+    vi.useFakeTimers({
+      toFake: ["Date"],
+      now: new Date("2026-06-19T22:30:00.000Z"),
+    });
+
+    // The evening used the whole ceiling, booked to the day that just ended.
+    await getPrismaClient().coachUsage.create({
+      data: {
+        userId: user.id,
+        dateKey: "2026-06-19",
+        totalTokens: 1000,
+        operatorTokens: 1000,
+        messageCount: 3,
+      },
+    });
+
+    const dateKey = await buildDateKey(user.id);
+    expect(dateKey).toBe("2026-06-20");
+    const first = await reserveBudget(
+      user.id,
+      200,
+      dateKey,
+      1000,
+      "operator",
+      "job",
+    );
+    expect(first.allowed).toBe(true);
+    const rows = await getPrismaClient().coachUsage.findMany({
+      where: { userId: user.id },
+      orderBy: { dateKey: "asc" },
+      select: { dateKey: true, totalTokens: true },
+    });
+    expect(rows).toEqual([
+      { dateKey: "2026-06-19", totalTokens: 1000 },
+      { dateKey: "2026-06-20", totalTokens: 200 },
+    ]);
+  });
+});
diff --git a/tests/integration/coach-chat.test.ts b/tests/integration/coach-chat.test.ts
index 9ae2ae8d9..bafa99d28 100644
--- a/tests/integration/coach-chat.test.ts
+++ b/tests/integration/coach-chat.test.ts
@@ -230,7 +230,9 @@ describe("POST /api/insights/chat — integration", () => {
     // the reservation is refunded so the ledger stays at the cap.
     const { userId } = await seedUserWithSession();
     const prisma = getPrismaClient();
-    const dateKey = new Date().toISOString().slice(0, 10);
+    // The account's own day, the key the route reserves under.
+    const { buildDateKey } = await import("@/lib/ai/coach/budget");
+    const dateKey = await buildDateKey(userId);
     // v1.21.0 — the daily cap is now provider-aware: the seeded user resolves
     // to a user-egress chain, so the applicable ceiling is USER_PLAN_CAP. Seed
     // the spend at that ceiling so the reservation trips the gate. (Seeding the
diff --git a/tests/integration/document-ai-runs.test.ts b/tests/integration/document-ai-runs.test.ts
index 2b82d6575..ffa9dbba5 100644
--- a/tests/integration/document-ai-runs.test.ts
+++ b/tests/integration/document-ai-runs.test.ts
@@ -483,7 +483,7 @@ describe("the reaper", () => {
     const { readDailySpend, buildDateKey } =
       await import("@/lib/ai/coach/budget");
     expect(
-      (await readDailySpend(user.id, buildDateKey())).total,
+      (await readDailySpend(user.id, await buildDateKey(user.id))).total,
     ).toBeGreaterThan(0);
 
     const { reapAiRuns } = await import("@/lib/documents/ai-runs/store");
@@ -493,7 +493,9 @@ describe("the reaper", () => {
       timedOut: 0,
       deleted: 0,
     });
-    expect((await readDailySpend(user.id, buildDateKey())).total).toBe(0);
+    expect(
+      (await readDailySpend(user.id, await buildDateKey(user.id))).total,
+    ).toBe(0);
 
     const run = await getPrismaClient().documentAiRun.findUniqueOrThrow({
       where: { id: runId },
diff --git a/tests/integration/rate-limit-429-headers.test.ts b/tests/integration/rate-limit-429-headers.test.ts
index 87800caef..db4608027 100644
--- a/tests/integration/rate-limit-429-headers.test.ts
+++ b/tests/integration/rate-limit-429-headers.test.ts
@@ -185,7 +185,7 @@ describe("429 rate-limit headers (real Postgres)", () => {
     await getPrismaClient().coachUsage.create({
       data: {
         userId: TEST_USER_ID,
-        dateKey: buildDateKey(),
+        dateKey: await buildDateKey(TEST_USER_ID),
         totalTokens: USER_PLAN_CAP,
         messageCount: 1,
       },