diff --git a/client/src/store/slices/daysSlice.test.ts b/client/src/store/slices/daysSlice.test.ts
index 0b36cbaa4..af182e7d3 100644
--- a/client/src/store/slices/daysSlice.test.ts
+++ b/client/src/store/slices/daysSlice.test.ts
@@ -42,6 +42,29 @@ describe('daysSlice', () => {
       expect(optimistic[0].title).toBe('Departure');
     });
 
+    it('FE-TSLICE-DAYS-001b: a day without a date moves to the front and keeps no date', async () => {
+      const days = [
+        buildDay({ id: 1, trip_id: 1, day_number: 1, date: '2025-06-01' }),
+        buildDay({ id: 2, trip_id: 1, day_number: 2, date: '2025-06-02' }),
+        buildDay({ id: 3, trip_id: 1, day_number: 3, date: null }),
+      ];
+      seedStore(useTripStore, { days });
+
+      let optimistic: Day[] = [];
+      server.use(
+        http.put('/api/trips/1/days/reorder', () => {
+          optimistic = useTripStore.getState().days;
+          return HttpResponse.json({ success: true });
+        }),
+        http.get('/api/trips/1/days', () => HttpResponse.json({ days })),
+      );
+
+      await useTripStore.getState().reorderDays(1, [3, 1, 2]);
+
+      expect(optimistic.map(d => d.id)).toEqual([3, 1, 2]);
+      expect(optimistic.map(d => d.date)).toEqual([null, '2025-06-01', '2025-06-02']);
+    });
+
     it('FE-TSLICE-DAYS-002: sends the requested order and refreshes days plus bookings', async () => {
       seedStore(useTripStore, { days: datedDays(), reservations: [] });
 
diff --git a/client/src/store/slices/daysSlice.ts b/client/src/store/slices/daysSlice.ts
index 4820b2706..30b2c0477 100644
--- a/client/src/store/slices/daysSlice.ts
+++ b/client/src/store/slices/daysSlice.ts
@@ -4,6 +4,7 @@ import type { StoreApi } from 'zustand'
 import type { TripStoreState } from '../tripStore'
 import type { Day } from '../../types'
 import { getApiErrorMessage } from '../../types'
+import { reorderedDayDates } from '@trek/shared'
 
 type SetState = StoreApi<TripStoreState>['setState']
 type GetState = StoreApi<TripStoreState>['getState']
@@ -47,12 +48,12 @@ export const createDaysSlice = (set: SetState, get: GetState): DaysSlice => ({
   reorderDays: async (tripId, orderedIds) => {
     const prevDays = get().days
     const byId = new Map(prevDays.map(d => [d.id, d]))
-    const sortedDates = prevDays.map(d => d.date).filter((d): d is string => !!d).sort((a, b) => (a < b ? -1 : a > b ? 1 : 0))
+    const dates = reorderedDayDates(prevDays, orderedIds)
     const optimistic = orderedIds
       .map((id, i) => {
         const d = byId.get(id)
         if (!d) return null
-        return { ...d, day_number: i + 1, date: sortedDates.length ? (sortedDates[i] ?? null) : d.date }
+        return { ...d, day_number: i + 1, date: dates.get(id) ?? null }
       })
       .filter((d): d is NonNullable<typeof d> => d !== null)
 
diff --git a/server/src/nest/days/days.mcp.ts b/server/src/nest/days/days.mcp.ts
index f1cfc52d0..b453a2683 100644
--- a/server/src/nest/days/days.mcp.ts
+++ b/server/src/nest/days/days.mcp.ts
@@ -157,7 +157,7 @@ export class DaysMcp {
   @Tool({
     name: 'reorder_days',
     description:
-      'Reorder the days of a trip by listing every one of its day IDs in the desired order. This moves whole days of the itinerary; to move places around inside a single day use reorder_day_assignments instead. Each day keeps its places, notes, stays and bookings, and on a dated trip the calendar dates stay pinned to their slots, so the content moves across the dates.',
+      'Reorder the days of a trip by listing every one of its day IDs in the desired order. This moves whole days of the itinerary; to move places around inside a single day use reorder_day_assignments instead. Each day keeps its places, notes, stays and bookings, and on a dated trip the calendar dates stay pinned to their slots, so the content moves across the dates; a day without a date keeps none wherever it is moved.',
     inputSchema: {
       tripId: idSchema,
       orderedIds: dayReorderRequestSchema.shape.orderedIds
diff --git a/server/src/nest/days/days.service.ts b/server/src/nest/days/days.service.ts
index aa3fb095c..a0b94be55 100644
--- a/server/src/nest/days/days.service.ts
+++ b/server/src/nest/days/days.service.ts
@@ -28,7 +28,7 @@ import { QueryHelpersService } from '../query-helpers/query-helpers.service';
 import { RealtimeService } from '../realtime/realtime.service';
 import { InjectRepository } from '@mikro-orm/nestjs';
 import { Injectable } from '@nestjs/common';
-import { addIsoDays, MAX_TRIP_DAYS, planDatedAppend } from '@trek/shared';
+import { addIsoDays, MAX_TRIP_DAYS, planDatedAppend, reorderedDayDates } from '@trek/shared';
 import type { RoadtripDayBoundary, TrekWsPayload, TrekWsTripEventName } from '@trek/shared';
 
 type Trip = TripAccess;
@@ -594,12 +594,9 @@ export class DaysService {
     }
 
     const oldDateById = new Map(rows.map((r) => [r.id, r.date]));
-    // Dates stay pinned to slots: position i keeps the i-th date (ascending).
-    const sortedDates = rows
-      .map((r) => r.date)
-      .filter((d): d is string => !!d)
-      .sort((a, b) => (a < b ? -1 : a > b ? 1 : 0));
-    const isDated = sortedDates.length > 0;
+    // Dates stay pinned to the slots of the dated days; a day without a date keeps none.
+    const newDates = reorderedDayDates(rows, orderedIds);
+    const isDated = rows.some((r) => !!r.date);
 
     await this.uow.transactional(async () => {
       // Two-phase renumber to dodge UNIQUE(trip_id, day_number) collisions —
@@ -610,7 +607,7 @@ export class DaysService {
       }
       const newDateById = new Map<number, string | null>();
       for (const [i, id] of orderedIds.entries()) {
-        const date = isDated ? (sortedDates[i] ?? null) : null;
+        const date = newDates.get(id) ?? null;
         await this.daysRepo.setDayNumberAndDate(id, i + 1, date);
         newDateById.set(id, date);
       }
diff --git a/server/tests/integration/dayReorder.test.ts b/server/tests/integration/dayReorder.test.ts
index 42a78ff11..732cae356 100644
--- a/server/tests/integration/dayReorder.test.ts
+++ b/server/tests/integration/dayReorder.test.ts
@@ -121,6 +121,18 @@ describe('reorderDays', () => {
     expect(r?.reservation_time).toBe('2026-03-01T19:00');
   });
 
+  it('moves a day without a date to the front of a dated trip without giving it a date', async () => {
+    const trip = createTrip(testDb, userId, { start_date: '2026-03-01', end_date: '2026-03-02' });
+    const [d1, d2] = await orderedDays(trip.id);
+    const extra = createDay(testDb, trip.id); // no date, appended as day 3
+
+    await reorderDays(trip.id, [extra.id, d1.id, d2.id]);
+
+    const after = await orderedDays(trip.id);
+    expect(after.map((d) => d.id)).toEqual([extra.id, d1.id, d2.id]);
+    expect(after.map((d) => d.date)).toEqual([null, '2026-03-01', '2026-03-02']);
+  });
+
   it('rejects an orderedIds list that is not a permutation of the trip days', async () => {
     const trip = createTrip(testDb, userId, { start_date: '2026-03-01', end_date: '2026-03-03' });
     const [d1, d2] = await orderedDays(trip.id);
diff --git a/shared/src/trip/day-grid.spec.ts b/shared/src/trip/day-grid.spec.ts
index b081b6f3c..a0df2cc32 100644
--- a/shared/src/trip/day-grid.spec.ts
+++ b/shared/src/trip/day-grid.spec.ts
@@ -5,6 +5,7 @@ import {
   nextTripDate,
   planDatedAppend,
   planDayGrid,
+  reorderedDayDates,
   resolveDayGridRange,
 } from './day-grid';
 import { MAX_TRIP_DAYS } from './trip.schema';
@@ -238,3 +239,38 @@ describe('planDayGrid', () => {
     });
   });
 });
+
+describe('reorderedDayDates', () => {
+  const days = [
+    { id: 1, date: '2026-10-01' },
+    { id: 2, date: '2026-10-02' },
+    { id: 3, date: '2026-10-03' },
+    { id: 4, date: null },
+  ];
+
+  it('keeps the dates on their slots while dated days change places', () => {
+    expect([...reorderedDayDates(days, [3, 1, 2, 4])]).toEqual([
+      [3, '2026-10-01'],
+      [1, '2026-10-02'],
+      [2, '2026-10-03'],
+      [4, null],
+    ]);
+  });
+
+  it('moves a day without a date to the front without handing it a date', () => {
+    expect([...reorderedDayDates(days, [4, 1, 2, 3])]).toEqual([
+      [4, null],
+      [1, '2026-10-01'],
+      [2, '2026-10-02'],
+      [3, '2026-10-03'],
+    ]);
+  });
+
+  it('leaves every day without a date on a trip without dates', () => {
+    const undated = [{ id: 1, date: null }, { id: 2 }];
+    expect([...reorderedDayDates(undated, [2, 1])]).toEqual([
+      [2, null],
+      [1, null],
+    ]);
+  });
+});
diff --git a/shared/src/trip/day-grid.ts b/shared/src/trip/day-grid.ts
index 59ac677aa..048418d24 100644
--- a/shared/src/trip/day-grid.ts
+++ b/shared/src/trip/day-grid.ts
@@ -66,6 +66,32 @@ export function planDatedAppend(
   return { date, fits: tripSpanDays(trip.start_date, date) <= MAX_TRIP_DAYS };
 }
 
+/**
+ * The date every day carries after the days are put in a new order. The dates stay
+ * with the positions, so content moves across the calendar, but only the dated days
+ * take part: a day without a date keeps none wherever it is moved, and the dated days
+ * take the trip's dates in ascending order as they now come. Handing out the dates by
+ * plain position instead gave a day added without a date the first date when it was
+ * moved to the front and took the date of the last dated day, so the undated row
+ * stayed at the end and the move looked as if nothing had happened.
+ */
+export function reorderedDayDates(
+  days: readonly { id: number; date?: string | null }[],
+  orderedIds: readonly number[],
+): Map<number, string | null> {
+  const dated = new Set(days.filter((d) => !!d.date).map((d) => d.id));
+  const sortedDates = days
+    .map((d) => d.date)
+    .filter((d): d is string => !!d)
+    .sort((a, b) => (a < b ? -1 : a > b ? 1 : 0));
+  const result = new Map<number, string | null>();
+  let next = 0;
+  for (const id of orderedIds) {
+    result.set(id, dated.has(id) ? (sortedDates[next++] ?? null) : null);
+  }
+  return result;
+}
+
 /** The dates and day count an update leaves a trip with, and whether its day rows are rebuilt. */
 export interface DayGridRange {
   newStart: string | null | undefined;