diff --git a/README.md b/README.md
index 6538134..08c09dd 100644
--- a/README.md
+++ b/README.md
@@ -98,6 +98,23 @@ export TIME_TRACK_DEVICE_ID="laptop-2026"
 
 Only finished entries are sent. Each completed entry receives a stable UUID. On first load after upgrading, historic entries are assigned UUIDs and the local data file is updated, so repeating a sync submits the same entry IDs for server-side idempotency. The active session is never uploaded.
 
+### Automatic sync (systemd user timer)
+
+A systemd user pair can run `sync` on a schedule:
+
+- `time-track-sync.service` (oneshot; reads `%h/.config/time-track-sync/env` and runs `time_track.py sync`)
+- `time-track-sync.timer` (every 15 minutes, `Persistent=true` to catch up after sleep)
+
+The env file holds the same three variables as above, with mode 600. Because the client re-sends all finished entries and the server dedupes by entry UUID, resending is safe; a race with a concurrently toggling tracker can at worst skip one cycle. The timer does not upload the active session.
+
+Useful commands:
+
+```sh
+systemctl --user start time-track-sync.service            # run a sync now
+systemctl --user list-timers time-track-sync.timer        # next scheduled run
+journalctl --user -u time-track-sync.service -f           # live logs
+```
+
 ## Waybar behavior
 
 - **Left click**: start or stop a session.