diff --git a/backend/src/common/zoned-civil-time.spec.ts b/backend/src/common/zoned-civil-time.spec.ts
index 99279ab..1fafc00 100644
--- a/backend/src/common/zoned-civil-time.spec.ts
+++ b/backend/src/common/zoned-civil-time.spec.ts
@@ -1,5 +1,9 @@
 import { appointmentWithinWorkingHours } from './working-hours';
-import { isValidIanaTimeZone, zonedWeekdayAndMinutes } from './zoned-civil-time';
+import {
+  civilDateInZone,
+  isValidIanaTimeZone,
+  zonedWeekdayAndMinutes,
+} from './zoned-civil-time';
 
 describe('zoned civil time', () => {
   it('accepts IANA zones and rejects garbage', () => {
@@ -20,10 +24,40 @@ describe('zoned civil time', () => {
     const start = new Date('2026-08-20T06:15:00.000Z');
     const end = new Date('2026-08-20T06:45:00.000Z');
     expect(
-      appointmentWithinWorkingHours(start, end, [{ startMinute: 8 * 60, endMinute: 17 * 60 }], 'Asia/Tehran'),
+      appointmentWithinWorkingHours(
+        start,
+        end,
+        [{ startMinute: 8 * 60, endMinute: 17 * 60 }],
+        'Asia/Tehran',
+      ),
     ).toBe(true);
     expect(
-      appointmentWithinWorkingHours(start, end, [{ startMinute: 8 * 60, endMinute: 17 * 60 }], 'UTC'),
+      appointmentWithinWorkingHours(
+        start,
+        end,
+        [{ startMinute: 8 * 60, endMinute: 17 * 60 }],
+        'UTC',
+      ),
     ).toBe(false);
   });
+  describe('civilDateInZone', () => {
+    it('gives the local civil date, which can differ from the UTC date', () => {
+      // 21:30 UTC is already the next day in Tehran (+03:30).
+      const instant = new Date('2025-10-11T21:30:00.000Z');
+      expect(civilDateInZone(instant, 'UTC')).toBe('2025-10-11');
+      expect(civilDateInZone(instant, 'Asia/Tehran')).toBe('2025-10-12');
+    });
+
+    it('gives the previous day for zones behind UTC just after midnight', () => {
+      const instant = new Date('2025-10-11T02:00:00.000Z');
+      expect(civilDateInZone(instant, 'America/New_York')).toBe('2025-10-10');
+      expect(civilDateInZone(instant, 'Europe/Amsterdam')).toBe('2025-10-11');
+    });
+
+    it('zero-pads single-digit months and days', () => {
+      expect(civilDateInZone(new Date('2025-01-05T12:00:00.000Z'), 'UTC')).toBe(
+        '2025-01-05',
+      );
+    });
+  });
 });
diff --git a/backend/src/common/zoned-civil-time.ts b/backend/src/common/zoned-civil-time.ts
index 88679ef..6a50fb4 100644
--- a/backend/src/common/zoned-civil-time.ts
+++ b/backend/src/common/zoned-civil-time.ts
@@ -53,3 +53,23 @@ export function civilDateJsWeekday(isoDate: string): number {
   const utcNoon = new Date(Date.UTC(y, m - 1, d, 12, 0, 0, 0));
   return utcNoon.getUTCDay();
 }
+
+/**
+ * Today's civil date (`YYYY-MM-DD`) in an IANA zone.
+ *
+ * Lets the server derive "today" from a client-supplied time zone instead of trusting a
+ * client-supplied date, which matters for relative deadlines like "by Thursday".
+ */
+export function civilDateInZone(date: Date, timeZone: string): string {
+  const parts = new Intl.DateTimeFormat('en-CA', {
+    timeZone,
+    year: 'numeric',
+    month: '2-digit',
+    day: '2-digit',
+  }).formatToParts(date);
+
+  const year = parts.find((p) => p.type === 'year')?.value ?? '1970';
+  const month = parts.find((p) => p.type === 'month')?.value ?? '01';
+  const day = parts.find((p) => p.type === 'day')?.value ?? '01';
+  return `${year}-${month}-${day}`;
+}
diff --git a/backend/src/modules/voice/due-date.resolver.spec.ts b/backend/src/modules/voice/due-date.resolver.spec.ts
new file mode 100644
index 0000000..db8599a
--- /dev/null
+++ b/backend/src/modules/voice/due-date.resolver.spec.ts
@@ -0,0 +1,221 @@
+import { resolveDueDate } from './due-date.resolver';
+import type { DueIntent } from './voice.types';
+
+// 2025-10-11 is a Saturday — the first day of the Iranian week.
+const SATURDAY = '2025-10-11';
+const THURSDAY = '2025-10-16';
+
+describe('resolveDueDate', () => {
+  describe('weekday intents', () => {
+    it('resolves "this <weekday>" to the coming occurrence in the same week', () => {
+      const result = resolveDueDate(
+        { kind: 'weekday', weekday: 'thursday', which: 'this' },
+        SATURDAY,
+      );
+      expect(result.dueDate).toBe(THURSDAY); // Sat -> Thu is 5 days in a Saturday-start week
+    });
+
+    it('resolves "next <weekday>" to the following week', () => {
+      const result = resolveDueDate(
+        { kind: 'weekday', weekday: 'thursday', which: 'next' },
+        SATURDAY,
+      );
+      expect(result.dueDate).toBe('2025-10-23');
+    });
+
+    it('reads "by Thursday" said on a Thursday as the next one, not today', () => {
+      // A deadline of today is almost never what was meant.
+      const result = resolveDueDate(
+        { kind: 'weekday', weekday: 'thursday', which: 'this' },
+        THURSDAY,
+      );
+      expect(result.dueDate).toBe('2025-10-23');
+    });
+
+    it('resolves the Saturday that starts the next week', () => {
+      const result = resolveDueDate(
+        { kind: 'weekday', weekday: 'saturday', which: 'this' },
+        SATURDAY,
+      );
+      expect(result.dueDate).toBe('2025-10-18');
+    });
+
+    it('rejects an unknown weekday or qualifier', () => {
+      expect(
+        resolveDueDate(
+          {
+            kind: 'weekday',
+            weekday: 'caturday',
+            which: 'this',
+          } as unknown as DueIntent,
+          SATURDAY,
+        ).dueDate,
+      ).toBeNull();
+      expect(
+        resolveDueDate(
+          {
+            kind: 'weekday',
+            weekday: 'thursday',
+            which: 'soon',
+          } as unknown as DueIntent,
+          SATURDAY,
+        ).dueDate,
+      ).toBeNull();
+    });
+  });
+
+  describe('offset intents', () => {
+    it('adds days, weeks and months', () => {
+      expect(
+        resolveDueDate({ kind: 'offset', unit: 'day', amount: 1 }, SATURDAY)
+          .dueDate,
+      ).toBe('2025-10-12');
+      expect(
+        resolveDueDate({ kind: 'offset', unit: 'week', amount: 1 }, SATURDAY)
+          .dueDate,
+      ).toBe('2025-10-18');
+      expect(
+        resolveDueDate({ kind: 'offset', unit: 'month', amount: 1 }, SATURDAY)
+          .dueDate,
+      ).toBe('2025-11-11');
+    });
+
+    it('clamps to the end of a shorter month', () => {
+      expect(
+        resolveDueDate(
+          { kind: 'offset', unit: 'month', amount: 1 },
+          '2025-01-31',
+        ).dueDate,
+      ).toBe('2025-02-28');
+      expect(
+        resolveDueDate(
+          { kind: 'offset', unit: 'month', amount: 1 },
+          '2024-01-31',
+        ).dueDate,
+      ).toBe('2024-02-29');
+    });
+
+    it('crosses a year boundary', () => {
+      expect(
+        resolveDueDate(
+          { kind: 'offset', unit: 'month', amount: 3 },
+          '2025-11-15',
+        ).dueDate,
+      ).toBe('2026-02-15');
+      expect(
+        resolveDueDate(
+          { kind: 'offset', unit: 'day', amount: 30 },
+          '2025-12-20',
+        ).dueDate,
+      ).toBe('2026-01-19');
+    });
+
+    it('rejects negative, fractional and absurd amounts', () => {
+      for (const amount of [-1, 1.5, 10_000, Number.NaN]) {
+        expect(
+          resolveDueDate({ kind: 'offset', unit: 'day', amount }, SATURDAY)
+            .dueDate,
+        ).toBeNull();
+      }
+    });
+  });
+
+  describe('jalali intents', () => {
+    it('converts by arithmetic, not inference', () => {
+      expect(
+        resolveDueDate({ kind: 'jalali', jy: 1404, jm: 7, jd: 25 }, SATURDAY)
+          .dueDate,
+      ).toBe('2025-10-17');
+    });
+
+    it('handles the leap-year Esfand 30', () => {
+      expect(
+        resolveDueDate(
+          { kind: 'jalali', jy: 1403, jm: 12, jd: 30 },
+          '2025-03-01',
+        ).dueDate,
+      ).toBe('2025-03-20');
+    });
+
+    it('rejects Esfand 30 in a non-leap year', () => {
+      const result = resolveDueDate(
+        { kind: 'jalali', jy: 1404, jm: 12, jd: 30 },
+        SATURDAY,
+      );
+      expect(result.dueDate).toBeNull();
+      expect(result.unresolved?.reason).toBe('invalid_date');
+    });
+  });
+
+  describe('gregorian intents', () => {
+    it('accepts a real date and rejects an impossible one', () => {
+      expect(
+        resolveDueDate({ kind: 'gregorian', y: 2025, m: 10, d: 17 }, SATURDAY)
+          .dueDate,
+      ).toBe('2025-10-17');
+      expect(
+        resolveDueDate({ kind: 'gregorian', y: 2025, m: 2, d: 30 }, SATURDAY)
+          .dueDate,
+      ).toBeNull();
+      expect(
+        resolveDueDate({ kind: 'gregorian', y: 2025, m: 13, d: 1 }, SATURDAY)
+          .dueDate,
+      ).toBeNull();
+    });
+  });
+
+  describe('guard rails', () => {
+    it('treats a past date as unresolved', () => {
+      const result = resolveDueDate(
+        { kind: 'gregorian', y: 2020, m: 1, d: 1 },
+        SATURDAY,
+      );
+      expect(result.dueDate).toBeNull();
+      expect(result.unresolved?.reason).toBe('invalid_date');
+    });
+
+    it('treats a date decades away as unresolved', () => {
+      expect(
+        resolveDueDate({ kind: 'gregorian', y: 2099, m: 1, d: 1 }, SATURDAY)
+          .dueDate,
+      ).toBeNull();
+    });
+
+    it('accepts today itself via a zero-day offset', () => {
+      expect(
+        resolveDueDate({ kind: 'offset', unit: 'day', amount: 0 }, SATURDAY)
+          .dueDate,
+      ).toBe(SATURDAY);
+    });
+
+    it('reports no due date at all when the model said nothing, without flagging it', () => {
+      expect(resolveDueDate(null, SATURDAY)).toEqual({
+        dueDate: null,
+        unresolved: null,
+      });
+      expect(resolveDueDate(undefined, SATURDAY)).toEqual({
+        dueDate: null,
+        unresolved: null,
+      });
+    });
+
+    it('degrades rather than throwing on a malformed today or intent', () => {
+      expect(
+        resolveDueDate({ kind: 'offset', unit: 'day', amount: 1 }, 'not-a-date')
+          .dueDate,
+      ).toBeNull();
+      expect(
+        resolveDueDate({ kind: 'nope' } as unknown as DueIntent, SATURDAY)
+          .dueDate,
+      ).toBeNull();
+    });
+
+    it('echoes what was heard so the review sheet can show it', () => {
+      const result = resolveDueDate(
+        { kind: 'jalali', jy: 1404, jm: 12, jd: 30 },
+        SATURDAY,
+      );
+      expect(result.unresolved?.spoken).toBe('1404/12/30');
+    });
+  });
+});
diff --git a/backend/src/modules/voice/due-date.resolver.ts b/backend/src/modules/voice/due-date.resolver.ts
new file mode 100644
index 0000000..0584e22
--- /dev/null
+++ b/backend/src/modules/voice/due-date.resolver.ts
@@ -0,0 +1,171 @@
+import { jalaliToIsoDate } from '../../common/jalali';
+import { civilDateJsWeekday } from '../../common/zoned-civil-time';
+import type { DueIntent, UnresolvedItem, Weekday } from './voice.types';
+
+/**
+ * Spoken deadline → ISO civil date.
+ *
+ * The model never does calendar arithmetic; it says what it heard and this decides what
+ * that means. Jalali conversion in particular is arithmetic here, not inference — an LLM
+ * asked to turn "۲۵ مهر" into ISO answers confidently and is often wrong, and
+ * `@IsDateString()` would accept the wrong answer.
+ *
+ * Works entirely in civil dates. The caller derives `todayIso` from the actor's IANA zone
+ * (see `civilDateInZone`) rather than passing a zone in here, so nothing in this file has
+ * to reason about instants.
+ */
+
+/** JS `getUTCDay()` numbering: Sunday = 0. */
+const WEEKDAY_TO_JS: Record<Weekday, number> = {
+  saturday: 6,
+  sunday: 0,
+  monday: 1,
+  tuesday: 2,
+  wednesday: 3,
+  thursday: 4,
+  friday: 5,
+};
+
+/** Refuse absurd deadlines however they were arrived at. */
+const MAX_DAYS_AHEAD = 365 * 5;
+
+export type DueResolution = {
+  dueDate: string | null;
+  unresolved: UnresolvedItem | null;
+};
+
+const ISO_DATE = /^\d{4}-\d{2}-\d{2}$/;
+
+function isRealCivilDate(iso: string): boolean {
+  if (!ISO_DATE.test(iso)) return false;
+  const [y, m, d] = iso.split('-').map(Number);
+  if (m < 1 || m > 12 || d < 1 || d > 31) return false;
+  const probe = new Date(Date.UTC(y, m - 1, d));
+  return (
+    probe.getUTCFullYear() === y &&
+    probe.getUTCMonth() === m - 1 &&
+    probe.getUTCDate() === d
+  );
+}
+
+function toIso(utcMs: number): string {
+  return new Date(utcMs).toISOString().slice(0, 10);
+}
+
+function utcMsOf(iso: string): number {
+  const [y, m, d] = iso.split('-').map(Number);
+  return Date.UTC(y, m - 1, d);
+}
+
+function addDays(iso: string, days: number): string {
+  return toIso(utcMsOf(iso) + days * 86_400_000);
+}
+
+/** Calendar-month addition with end-of-month clamping (31 Jan + 1 month = 28/29 Feb). */
+function addMonths(iso: string, months: number): string {
+  const [y, m, d] = iso.split('-').map(Number);
+  const targetMonthIndex = m - 1 + months;
+  const targetYear = y + Math.floor(targetMonthIndex / 12);
+  const targetMonth = ((targetMonthIndex % 12) + 12) % 12;
+  const lastDay = new Date(
+    Date.UTC(targetYear, targetMonth + 1, 0),
+  ).getUTCDate();
+  return toIso(Date.UTC(targetYear, targetMonth, Math.min(d, lastDay)));
+}
+
+function unresolved(spoken: string): DueResolution {
+  return { dueDate: null, unresolved: { spoken, reason: 'invalid_date' } };
+}
+
+function describe(intent: DueIntent): string {
+  switch (intent?.kind) {
+    case 'weekday':
+      return `${intent.which} ${intent.weekday}`;
+    case 'offset':
+      return `+${intent.amount} ${intent.unit}`;
+    case 'jalali':
+      return `${intent.jy}/${intent.jm}/${intent.jd}`;
+    case 'gregorian':
+      return `${intent.y}-${intent.m}-${intent.d}`;
+    default:
+      return '';
+  }
+}
+
+/**
+ * `which: 'this'` means the soonest occurrence strictly after today, so "by Thursday" said
+ * on a Thursday means the next one — a deadline of today is almost never what was meant.
+ * `'next'` adds a further week. The Iranian week starts Saturday, which this arithmetic is
+ * agnostic to (it counts forward from today), but the tests pin it explicitly.
+ */
+function resolveWeekday(
+  intent: Extract<DueIntent, { kind: 'weekday' }>,
+  todayIso: string,
+) {
+  const targetJs = WEEKDAY_TO_JS[intent.weekday];
+  if (targetJs === undefined) return null;
+  if (intent.which !== 'this' && intent.which !== 'next') return null;
+
+  const todayJs = civilDateJsWeekday(todayIso);
+  let delta = (targetJs - todayJs + 7) % 7;
+  if (delta === 0) delta = 7;
+  if (intent.which === 'next') delta += 7;
+  return addDays(todayIso, delta);
+}
+
+function resolveOffset(
+  intent: Extract<DueIntent, { kind: 'offset' }>,
+  todayIso: string,
+) {
+  const { amount, unit } = intent;
+  if (!Number.isInteger(amount) || amount < 0) return null;
+  if (unit === 'day')
+    return amount <= MAX_DAYS_AHEAD ? addDays(todayIso, amount) : null;
+  if (unit === 'week')
+    return amount <= 260 ? addDays(todayIso, amount * 7) : null;
+  if (unit === 'month')
+    return amount <= 60 ? addMonths(todayIso, amount) : null;
+  return null;
+}
+
+export function resolveDueDate(
+  intent: DueIntent | null | undefined,
+  todayIso: string,
+): DueResolution {
+  if (!intent || typeof intent !== 'object') {
+    return { dueDate: null, unresolved: null };
+  }
+  if (!isRealCivilDate(todayIso)) {
+    return unresolved(describe(intent));
+  }
+
+  let resolved: string | null = null;
+  switch (intent.kind) {
+    case 'weekday':
+      resolved = resolveWeekday(intent, todayIso);
+      break;
+    case 'offset':
+      resolved = resolveOffset(intent, todayIso);
+      break;
+    case 'jalali':
+      resolved = jalaliToIsoDate(intent.jy, intent.jm, intent.jd);
+      break;
+    case 'gregorian': {
+      const candidate = `${String(intent.y).padStart(4, '0')}-${String(intent.m).padStart(2, '0')}-${String(intent.d).padStart(2, '0')}`;
+      resolved = isRealCivilDate(candidate) ? candidate : null;
+      break;
+    }
+    default:
+      resolved = null;
+  }
+
+  if (!resolved) return unresolved(describe(intent));
+
+  // An absolute date the model invented can land anywhere; a deadline in the past or
+  // decades away is not a deadline.
+  const daysAhead = (utcMsOf(resolved) - utcMsOf(todayIso)) / 86_400_000;
+  if (daysAhead < 0 || daysAhead > MAX_DAYS_AHEAD)
+    return unresolved(describe(intent));
+
+  return { dueDate: resolved, unresolved: null };
+}