WatchTimeStopwatch
A big, precise stopwatch with lap times. Start it, switch tabs, come back — the elapsed time stays correct, because it's computed from timestamps rather than counted tick by tick.
| Lap | Lap time | Total |
|---|
Runs entirely in your browser and needs JavaScript. Nothing is stored; reloading the page resets the stopwatch.
How the stopwatch keeps time
A naive stopwatch adds a hundredth of a second every time a timer fires — and drifts, because browsers don't fire timers with perfect regularity, and they deliberately slow timers down in background tabs to save battery. This stopwatch works differently: it records the moment you press Start on the browser's monotonic clock and, on every screen refresh, displays the difference between then and now. The display can freeze while a tab is hidden, but the arithmetic can't drift — bring the tab back and the elapsed time is exactly right.
The monotonic clock also means the stopwatch is immune to system clock changes. If your computer syncs with a time server, or you cross a time zone mid-timing, a wall-clock-based stopwatch would jump; a monotonic one just keeps counting forward, which is the entire job of a stopwatch.
Precision versus reaction time
The display shows hundredths of a second, and the underlying measurement is finer still. But for anything timed by hand, the dominant error is you: human reaction time to a visual cue averages around a quarter of a second, at both the start and the stop. Hand-timed results are honest to about the nearest half second — which is why athletics stopped accepting hand timing for records and moved to automatic timing decades ago. For cooking, workouts, presentations, and board games, hundredths are plenty.
Frequently asked questions
Does it keep timing if I switch tabs or lock my phone?
Yes. The elapsed time is computed from the start timestamp, so it stays correct no matter how long the tab was hidden. The on-screen digits may pause while hidden, then snap to the right value when you return.
What happens if I close the tab?
The stopwatch resets — nothing is stored, by design. If you need timing that survives a closed tab, note the start time and use the moment of stopping with the date calculator or a timestamp instead.
What's the difference between a lap time and the total?
The lap column shows the time since the previous lap press; the total column shows time since Start. Runners use laps for splits; the same works for timing rounds, sets, or speakers in a meeting.
Counting down to a fixed moment instead of up from one? Use the countdown timer.