Time study or exam practice
Count down 25 minutes and be reminded by the chime and the desktop notification.
Loading…
Guide
The page has a stopwatch and a countdown. The stopwatch accumulates elapsed time with performance.now() and refreshes the display about every 31 ms, recording each lap and the cumulative time; the countdown stores an end time of Date.now() + remaining and recomputes the remaining value about every 200 ms, which reduces the cumulative drift caused by a background timer being delayed.
Updated 2026-09-272 min read
Pausing the stopwatch adds the current performance.now() difference to the baseline; when the countdown returns from the background it corrects directly against the absolute end time rather than simply subtracting 200 ms each time.
Count down 25 minutes and be reminded by the chime and the desktop notification.
Take laps on the stopwatch and review each lap and the cumulative time.
Use the 1, 3, 5 or 10 minute presets instead of reaching for a built-in phone app.
The display update may be throttled, but the remaining time is recalculated from the end time.
Timing data is handled only in the current page's memory; notifications are sent locally by the browser, so no countdown content has to be uploaded to a server.
Updated 2026-09-27
Millisecond stopwatch with laps, and a countdown with end chime and desktop notification
00:00.00