NumberTally Stopwatch
A precise online stopwatch with lap times, keyboard control, and a best-session memory. Timing uses your device clock — not interval counting — so it stays accurate even in background tabs.
00:00.00
minutes : seconds . centiseconds
Tip: press Space to start / pause.
Why this stopwatch stays accurate
Cheap timers count interval ticks ("add 10ms every tick"), which drifts whenever the browser throttles background tabs or the event loop lags. This stopwatch instead records performance.now() timestamps at start, pause, and lap — and computes elapsed time as the difference. The display refreshes on a 10ms interval, but the measured time comes from the clock, so pausing the tab for an hour changes nothing.
Lap times, explained
Each lap records two numbers: the lap time (how long since the previous lap — useful for runners, swimmers, and speakers timing sections) and the total (time since start). The fastest lap is highlighted automatically. Your longest session and most recent session are remembered in this browser.
Frequently Asked Questions
Does the stopwatch keep running if I switch tabs?
Yes. Elapsed time is computed from clock timestamps, so background throttling only pauses the display refresh — the measured time stays exact.
What is the "best session" it remembers?
Your longest completed session (the biggest total when you pressed Reset after running). It and your last session are stored only in this browser's local storage.
How precise is it?
The display shows centiseconds (1/100 s). Under the hood, performance.now() resolves to microseconds, so lap ordering is reliable even for photo finishes.
Why does Space sometimes not work?
Space toggles start/pause unless your cursor is inside a text field or a button has focus (then Space activates that control instead). Click the page background first.
Can I use it for interval training?
Yes — press Lap at each interval boundary. The lap table shows every split with the fastest one highlighted, which works well for run/walk or HIIT timing.