diff --git a/apps/api/src/lib/csv.ts b/apps/api/src/lib/csv.ts
index 67ba557..7e78596 100644
--- a/apps/api/src/lib/csv.ts
+++ b/apps/api/src/lib/csv.ts
@@ -11,3 +11,62 @@ export function formatDuration(totalSeconds: number): string {
   const sec = s % 60;
   return `${String(h).padStart(2, '0')}:${String(m).padStart(2, '0')}:${String(sec).padStart(2, '0')}`;
 }
+
+// One completed session, flattened for CSV. Times accept Date | number | string.
+export interface SessionCsvRow {
+  id: number;
+  activityName: string | null;
+  userName?: string | null;
+  insoleType: string | null;
+  pairCount: number;
+  startTime: Date | number | string;
+  endTime: Date | number | string | null;
+  durationSeconds: number | null;
+  pausedSeconds: number | null;
+}
+
+// Build the CSV body shared by the worker self-export and the admin all-users export.
+// includeWorker prepends a Worker column; everything else matches the legacy format byte-for-byte.
+export function buildSessionsCsv(
+  rows: SessionCsvRow[],
+  opts: { includeWorker?: boolean } = {},
+): string {
+  const includeWorker = opts.includeWorker ?? false;
+  const header = [
+    ...(includeWorker ? ['Worker'] : []),
+    'ID',
+    'Task',
+    'Insole Type',
+    'No. of Insoles',
+    'Date',
+    'Total Duration',
+    'Paused Duration',
+    'Start Time',
+    'End Time',
+  ]
+    .map(quote)
+    .join(',');
+
+  const dataLines = rows.map((row) => {
+    const start = new Date(row.startTime);
+    const end = row.endTime ? new Date(row.endTime) : null;
+    return [
+      ...(includeWorker ? [row.userName ?? ''] : []),
+      row.id,
+      row.activityName ?? '',
+      row.insoleType ?? 'Kurk',
+      row.pairCount ?? 2,
+      start.toLocaleDateString('nl-BE', { day: '2-digit', month: '2-digit', year: 'numeric' }),
+      formatDuration(row.durationSeconds ?? 0),
+      formatDuration(row.pausedSeconds ?? 0),
+      start.toLocaleTimeString('nl-BE', { hour: '2-digit', minute: '2-digit', second: '2-digit' }),
+      end
+        ? end.toLocaleTimeString('nl-BE', { hour: '2-digit', minute: '2-digit', second: '2-digit' })
+        : '',
+    ]
+      .map(quote)
+      .join(',');
+  });
+
+  return [header, ...dataLines].join('\n');
+}
diff --git a/apps/api/src/routes/sessions.ts b/apps/api/src/routes/sessions.ts
index f08369a..4b2fa77 100644
--- a/apps/api/src/routes/sessions.ts
+++ b/apps/api/src/routes/sessions.ts
@@ -5,7 +5,7 @@ import { db } from '../db/client';
 import { activities, workSessions } from '../db/schema';
 import { getSessionUser } from '../lib/require-user';
 import { toWorkSession } from '../lib/work-session';
-import { quote, formatDuration } from '../lib/csv';
+import { buildSessionsCsv } from '../lib/csv';
 
 export const sessionsRoutes = new Hono();
 
@@ -20,45 +20,18 @@ sessionsRoutes.get('/api/export', async (c) => {
     .where(and(eq(workSessions.userId, sessionUser.id), eq(workSessions.status, 'completed')))
     .orderBy(asc(workSessions.startTime));
 
-  const header = [
-    'ID',
-    'Task',
-    'Insole Type',
-    'No. of Insoles',
-    'Date',
-    'Total Duration',
-    'Paused Duration',
-    'Start Time',
-    'End Time',
-  ]
-    .map(quote)
-    .join(',');
-
-  const dataLines = rows.map(({ session, activityName }) => {
-    const start = new Date(session.startTime);
-    const end = session.endTime ? new Date(session.endTime) : null;
-    return [
-      session.id,
-      activityName ?? '',
-      session.insoleType ?? 'Kurk',
-      session.pairCount ?? 2,
-      start.toLocaleDateString('nl-BE', { day: '2-digit', month: '2-digit', year: 'numeric' }),
-      formatDuration(session.durationSeconds ?? 0),
-      formatDuration(session.pausedSeconds ?? 0),
-      start.toLocaleTimeString('nl-BE', {
-        hour: '2-digit',
-        minute: '2-digit',
-        second: '2-digit',
-      }),
-      end
-        ? end.toLocaleTimeString('nl-BE', { hour: '2-digit', minute: '2-digit', second: '2-digit' })
-        : '',
-    ]
-      .map(quote)
-      .join(',');
-  });
-
-  const csv = [header, ...dataLines].join('\n');
+  const csv = buildSessionsCsv(
+    rows.map(({ session, activityName }) => ({
+      id: session.id,
+      activityName,
+      insoleType: session.insoleType,
+      pairCount: session.pairCount,
+      startTime: session.startTime,
+      endTime: session.endTime,
+      durationSeconds: session.durationSeconds,
+      pausedSeconds: session.pausedSeconds,
+    })),
+  );
 
   return c.body(csv, 200, {
     'Content-Type': 'text/csv; charset=utf-8',
diff --git a/apps/api/test/csv.test.ts b/apps/api/test/csv.test.ts
new file mode 100644
index 0000000..ab2967a
--- /dev/null
+++ b/apps/api/test/csv.test.ts
@@ -0,0 +1,34 @@
+import { describe, it, expect } from 'vitest';
+import { buildSessionsCsv, type SessionCsvRow } from '../src/lib/csv';
+
+const row: SessionCsvRow = {
+  id: 7,
+  activityName: 'Frezen',
+  userName: 'Jan',
+  insoleType: 'Kurk',
+  pairCount: 2,
+  startTime: new Date('2026-06-17T08:00:00Z'),
+  endTime: new Date('2026-06-17T08:01:30Z'),
+  durationSeconds: 90,
+  pausedSeconds: 0,
+};
+
+describe('buildSessionsCsv', () => {
+  it('omits the Worker column by default (legacy header)', () => {
+    const lines = buildSessionsCsv([row]).split('\n');
+    expect(lines[0]).toBe(
+      '"ID","Task","Insole Type","No. of Insoles","Date","Total Duration","Paused Duration","Start Time","End Time"',
+    );
+    expect(lines[1]).toContain('"Frezen"');
+    expect(lines[1]).toContain('"00:01:30"');
+    expect(lines[1]).not.toContain('"Jan"');
+  });
+
+  it('prepends a Worker column when includeWorker is true', () => {
+    const lines = buildSessionsCsv([row], { includeWorker: true }).split('\n');
+    expect(lines[0]).toBe(
+      '"Worker","ID","Task","Insole Type","No. of Insoles","Date","Total Duration","Paused Duration","Start Time","End Time"',
+    );
+    expect(lines[1].startsWith('"Jan"')).toBe(true);
+  });
+});