diff --git a/server/src/nest/atlas/atlas.service.ts b/server/src/nest/atlas/atlas.service.ts
index 0bbfd2acf..b966b9a0d 100644
--- a/server/src/nest/atlas/atlas.service.ts
+++ b/server/src/nest/atlas/atlas.service.ts
@@ -337,9 +337,10 @@ export class AtlasService {
     FROM reservation_endpoints e
     JOIN reservations r ON e.reservation_id = r.id
     WHERE r.trip_id IN (${tripIds.map(() => '?').join(',')}) AND e.role IN ('from', 'to')
+      AND ${AtlasService.TRAVELER_OWNS}
   `,
       )
-      .all(...tripIds) as EndpointRow[];
+      .all(...tripIds, userId) as EndpointRow[];
 
     // A layover the traveler never left is only marked 'stop' while both its legs sit in
     // one booking. Split over two bookings it is a plain 'to' plus 'from' at the same
@@ -1004,7 +1005,8 @@ export class AtlasService {
     WHERE (t.user_id = ? OR tm.user_id = ?) AND e.role IN ('from', 'to')
       AND COALESCE(t.start_date, t.end_date) IS NOT NULL
       AND COALESCE(t.start_date, t.end_date) <= date('now')
-  `, userId, userId);
+      AND ${AtlasService.TRAVELER_OWNS}
+  `, userId, userId, userId);
     const transfers = transferEndpointIds(
       endpointRows.filter(e => e.reservation_type === 'flight' && e.reservation_status !== 'cancelled')
     );
@@ -1043,6 +1045,25 @@ export class AtlasService {
    * between consecutive points are added up so multi-stop flights count
    * correctly.
    */
+  /**
+   * Whether a reservation counts toward one person's own travel figures.
+   *
+   * It does when they are named on it (#1517 assigns members and guests to
+   * bookings), and it does when nobody is named at all — an unassigned booking
+   * still belongs to the whole trip, which is what every reservation made
+   * before 4.0 looks like.
+   *
+   * That second half is what keeps this from being a breaking change: the
+   * assignment table is empty on any install upgrading from 3.4.1, and a plain
+   * join would have taken those users' flown distance to zero overnight. With
+   * no assignments anywhere the result is identical to before (#1966).
+   *
+   * Binds ONE parameter, the user id, and expects the reservation aliased `r`.
+   */
+  private static readonly TRAVELER_OWNS = `
+    (NOT EXISTS (SELECT 1 FROM reservation_travelers rt WHERE rt.reservation_id = r.id)
+     OR EXISTS (SELECT 1 FROM reservation_travelers rt WHERE rt.reservation_id = r.id AND rt.user_id = ?))`;
+
   private flightDistanceKm(userId: number): number {
     const rows = this.db.all<{ reservation_id: number; lat: number; lng: number }>(`
       SELECT re.reservation_id, re.lat, re.lng
@@ -1053,8 +1074,9 @@ export class AtlasService {
       WHERE (t.user_id = ? OR tm.user_id IS NOT NULL)
         AND r.type = 'flight'
         AND r.status != 'cancelled'
+        AND ${AtlasService.TRAVELER_OWNS}
       ORDER BY re.reservation_id, re.sequence
-    `, userId, userId);
+    `, userId, userId, userId);
 
     let total = 0;
     let prev: { id: number; lat: number; lng: number } | null = null;
diff --git a/server/tests/unit/nest/travel-stats.service.test.ts b/server/tests/unit/nest/travel-stats.service.test.ts
index d24d9289d..4f62e5859 100644
--- a/server/tests/unit/nest/travel-stats.service.test.ts
+++ b/server/tests/unit/nest/travel-stats.service.test.ts
@@ -27,7 +27,7 @@ import { describe, it, expect, beforeAll, beforeEach, afterAll, vi } from 'vites
 import { createTables } from '../../../src/db/schema';
 import { runMigrations } from '../../../src/db/migrations';
 import { resetTestDb } from '../../helpers/test-db';
-import { createUser, createTrip, createPlace, createReservation } from '../../helpers/factories';
+import { createUser, createTrip, createPlace, createReservation, addTripMember } from '../../helpers/factories';
 import { AtlasService } from '../../../src/nest/atlas/atlas.service';
 import { DatabaseService } from '../../../src/nest/database/database.service';
 
@@ -226,3 +226,109 @@ describe('travel-stats quirk fixes', () => {
     expect(stats.coords).toContainEqual({ lat: 0, lng: 0 });
   });
 });
+
+/**
+ * Whose trip it is, and whose flight (#1966).
+ *
+ * 4.0 lets a booking name the people it is for (#1517), and the figures never
+ * read that: they scoped by trip membership, so on a shared trip everyone was
+ * credited with everyone's flights. Two people flying to the same place from
+ * different cities each got both departures, and the countries each of them had
+ * "visited" included the other's.
+ *
+ * The rule has a second half that matters more than the first: a booking with
+ * nobody named on it still counts for everyone. Every reservation made before
+ * 4.0 looks exactly like that, so without it this would have taken the flown
+ * distance of every existing install to zero.
+ */
+describe('personal figures on a shared trip (#1966)', () => {
+  const PAST_START = '2023-05-01';
+  const PAST_END = '2023-05-10';
+
+  const endpoint = (reservationId: number, role: 'from' | 'to', sequence: number, lat: number, lng: number, code: string) =>
+    testDb.prepare(
+      'INSERT INTO reservation_endpoints (reservation_id, role, sequence, name, lat, lng, code) VALUES (?, ?, ?, ?, ?, ?, ?)'
+    ).run(reservationId, role, sequence, `Endpoint ${sequence}`, lat, lng, code);
+
+  const assignTo = (reservationId: number, userId: number) =>
+    testDb.prepare('INSERT INTO reservation_travelers (reservation_id, user_id) VALUES (?, ?)').run(reservationId, userId);
+
+  /** A shared trip: A flies Rome→New York, B flies Mexico City→New York. */
+  function sharedTrip() {
+    const { user: alice } = createUser(testDb);
+    const { user: bob } = createUser(testDb);
+    const trip = createTrip(testDb, alice.id, { title: 'Shared', start_date: PAST_START, end_date: PAST_END });
+    addTripMember(testDb, trip.id, bob.id);
+
+    const fromRome = createReservation(testDb, trip.id, { type: 'flight', title: 'FCO-JFK' });
+    endpoint(fromRome.id, 'from', 0, 41.8003, 12.2389, 'FCO');
+    endpoint(fromRome.id, 'to', 1, 40.6413, -73.7781, 'JFK');
+
+    const fromMexico = createReservation(testDb, trip.id, { type: 'flight', title: 'MEX-JFK' });
+    endpoint(fromMexico.id, 'from', 0, 19.4363, -99.0721, 'MEX');
+    endpoint(fromMexico.id, 'to', 1, 40.6413, -73.7781, 'JFK');
+
+    return { alice, bob, trip, fromRome, fromMexico };
+  }
+
+  it('credits each traveler with their own flight only', () => {
+    const { alice, bob, fromRome, fromMexico } = sharedTrip();
+    assignTo(fromRome.id, alice.id);
+    assignTo(fromMexico.id, bob.id);
+
+    const a = atlas.getTravelStats(alice.id);
+    const b = atlas.getTravelStats(bob.id);
+
+    // Rome to New York is a good deal further than Mexico City to New York, so
+    // equal distances would mean both are still counting both flights.
+    expect(a.totalDistanceKm).toBeGreaterThan(0);
+    expect(b.totalDistanceKm).toBeGreaterThan(0);
+    expect(a.totalDistanceKm).not.toBe(b.totalDistanceKm);
+  });
+
+  it('does not stamp another traveler s departure country on your passport', () => {
+    const { alice, bob, fromRome, fromMexico } = sharedTrip();
+    assignTo(fromRome.id, alice.id);
+    assignTo(fromMexico.id, bob.id);
+
+    // Alice never went through Mexico.
+    expect(atlas.getTravelStats(alice.id).countries).not.toContain('MX');
+    expect(atlas.getTravelStats(bob.id).countries).not.toContain('IT');
+  });
+
+  /*
+   * The case that keeps this from being a breaking change. The assignment table
+   * is empty on every install upgrading from 3.4.1.
+   */
+  it('still counts a booking nobody is named on, for everyone on the trip', () => {
+    const { alice, bob } = sharedTrip();
+
+    const a = atlas.getTravelStats(alice.id);
+    const b = atlas.getTravelStats(bob.id);
+    expect(a.totalDistanceKm).toBeGreaterThan(0);
+    expect(a.totalDistanceKm).toBe(b.totalDistanceKm);
+  });
+
+  it('counts a booking they are both named on, once for each of them', () => {
+    const { alice, bob, fromRome, fromMexico } = sharedTrip();
+    assignTo(fromRome.id, alice.id);
+    assignTo(fromRome.id, bob.id);
+    assignTo(fromMexico.id, alice.id);
+    assignTo(fromMexico.id, bob.id);
+
+    const a = atlas.getTravelStats(alice.id);
+    const b = atlas.getTravelStats(bob.id);
+    expect(a.totalDistanceKm).toBe(b.totalDistanceKm);
+    expect(a.countries).toEqual(b.countries);
+  });
+
+  it('leaves a traveler assigned nothing with the unassigned bookings only', () => {
+    const { alice, bob, fromRome } = sharedTrip();
+    assignTo(fromRome.id, bob.id);
+
+    // Alice keeps the Mexico flight (nobody named) but loses the Rome one.
+    const a = atlas.getTravelStats(alice.id);
+    expect(a.countries).not.toContain('IT');
+    expect(a.totalDistanceKm).toBeGreaterThan(0);
+  });
+});