diff --git a/server/src/routes/etl.ts b/server/src/routes/etl.ts
index 53f065d..145caba 100644
--- a/server/src/routes/etl.ts
+++ b/server/src/routes/etl.ts
@@ -1,34 +1,58 @@
 import { Router, Request, Response } from 'express';
 import { etl } from '../config';
-import { runSync } from '../services/etlSync';
+import { runSync, SyncResult } from '../services/etlSync';
 
 const router = Router();
 
-// POST /api/etl/sync?mode=full|incremental
-router.post('/sync', async (req: Request, res: Response) => {
-  // Auth check
-  const auth = req.headers.authorization;
-  if (etl.secret && auth !== `Bearer ${etl.secret}`) {
+type SyncState =
+  | { status: 'idle' }
+  | { status: 'running'; mode: string; startedAt: string; currentMonth?: string }
+  | { status: 'done'; result: SyncResult; finishedAt: string }
+  | { status: 'error'; error: string; finishedAt: string };
+
+let syncState: SyncState = { status: 'idle' };
+
+function auth(req: Request, res: Response): boolean {
+  const header = req.headers.authorization;
+  if (etl.secret && header !== `Bearer ${etl.secret}`) {
     res.status(401).json({ error: 'Unauthorized' });
+    return false;
+  }
+  return true;
+}
+
+// POST /api/etl/sync?mode=full|incremental — fires and returns immediately
+router.post('/sync', (req: Request, res: Response) => {
+  if (!auth(req, res)) return;
+
+  if (syncState.status === 'running') {
+    res.status(409).json({ error: 'Sync already running', state: syncState });
     return;
   }
 
   const mode = (req.query.mode as string) === 'full' ? 'full' : 'incremental';
+  syncState = { status: 'running', mode, startedAt: new Date().toISOString() };
 
-  try {
-    console.log(`\nETL sync started (${mode})...`);
-    const result = await runSync(mode);
-    console.log(`ETL sync complete: ${result.transactionsFetched} transactions → ${result.recordsWritten} records in ${result.duration}`);
-    res.json(result);
-  } catch (err) {
-    console.error('ETL sync failed:', (err as Error).message);
-    res.status(500).json({ error: 'ETL sync failed', details: (err as Error).message });
-  }
+  res.json({ accepted: true, mode, message: 'Sync started — poll GET /api/etl/status for progress' });
+
+  console.log(`\nETL sync started (${mode})...`);
+  runSync(mode, (month) => {
+    if (syncState.status === 'running') syncState = { ...syncState, currentMonth: month };
+  })
+    .then(result => {
+      console.log(`ETL sync complete: ${result.transactionsFetched} transactions → ${result.recordsWritten} records in ${result.duration}`);
+      syncState = { status: 'done', result, finishedAt: new Date().toISOString() };
+    })
+    .catch(err => {
+      console.error('ETL sync failed:', (err as Error).message);
+      syncState = { status: 'error', error: (err as Error).message, finishedAt: new Date().toISOString() };
+    });
 });
 
 // GET /api/etl/status
-router.get('/status', (_req: Request, res: Response) => {
-  res.json({ configured: !!etl.secret });
+router.get('/status', (req: Request, res: Response) => {
+  if (!auth(req, res)) return;
+  res.json(syncState);
 });
 
 export default router;
diff --git a/server/src/services/etlSync.ts b/server/src/services/etlSync.ts
index e7572ae..6030255 100644
--- a/server/src/services/etlSync.ts
+++ b/server/src/services/etlSync.ts
@@ -96,7 +96,7 @@ export interface SyncResult {
   duration: string;
 }
 
-export async function runSync(mode: 'full' | 'incremental' = 'incremental'): Promise<SyncResult> {
+export async function runSync(mode: 'full' | 'incremental' = 'incremental', onMonth?: (month: string) => void): Promise<SyncResult> {
   const start = Date.now();
 
   const tables = await discoverTableIds();
@@ -113,7 +113,9 @@ export async function runSync(mode: 'full' | 'incremental' = 'incremental'): Pro
   // Fetch from ERP sequentially (API can't handle concurrent requests)
   const allSales: ERPSaleRecord[] = [];
   for (const [startDate, endDate] of months) {
-    console.log(`  Fetching ${startDate.slice(0, 7)}...`);
+    const monthLabel = startDate.slice(0, 7);
+    console.log(`  Fetching ${monthLabel}...`);
+    onMonth?.(monthLabel);
     const chunk = await fetchSales(startDate, endDate) as ERPSaleRecord[];
     allSales.push(...chunk);
   }