Stopwatch & Lap Timer
A precise stopwatch with lap splits, fastest and slowest markers and CSV export.
Timing That Does Not Drift
A stopwatch built on the system clock has a subtle flaw: the system clock is corrected. If a time sync happens mid-session, the elapsed time jumps — forwards or backwards — and a long measurement is quietly wrong.
This one uses the browser's monotonic clock, which only ever moves forwards at a constant rate and is unaffected by clock corrections, time zone changes or the machine sleeping. Over a long session that is the difference between a measurement and a guess.
Key features
- Monotonic timing — unaffected by system clock corrections, which is what makes long sessions trustworthy.
- Lap splits and totals — each lap's own time alongside the elapsed time when it was recorded.
- Fastest and slowest marked — with a bar per lap, so the pattern is visible without reading numbers.
- Keyboard control — space to start and stop, L for a lap, R to reset.
- CSV export — both the formatted times and the raw milliseconds, for analysis elsewhere.
This tool runs entirely inside your browser using native Web APIs. Your files and text are never uploaded to a server, never logged and never shared with third parties.
How to use: Stopwatch & Lap Timer
- Start the clock
Click start, or press the space bar. - Record laps
Press L or click Lap. Each one records its own split and the elapsed total. - Read the pattern
The fastest and slowest are marked, with a bar showing each lap against the slowest. - Export if you need to
The CSV carries both formatted times and raw milliseconds.
Technical specifications
| Processing location | Entirely in your browser — no server round trip |
|---|---|
| Data uploaded | None. Files and text never leave your device |
| Price | Free — no account, no trial, no usage cap |
| Category | Calculators |
| Works offline | Yes, once the page has loaded |
| Browser support | Chrome 90+, Edge 90+, Firefox 90+, Safari 15+ |
| Interface languages | English, 中文, हिन्दी, Español, العربية |
Frequently asked questions
How accurate is it?
The underlying timing is accurate to well under a millisecond, and the laps are stored at that precision. The practical limit is human reaction time, which is around 200 milliseconds — so for anything hand-timed, the stopwatch is far more precise than the person operating it.
Does it keep running if I switch tabs?
Yes. Elapsed time is calculated from timestamps rather than counted by a timer, so a background tab that stops being repainted loses nothing — the display simply catches up when you come back. Recording a lap does need the tab to be in front, since you have to press the key.
What is the difference between a split and an elapsed time?
The split is that lap on its own — the time since the previous lap. The elapsed time is the total since the clock started. A runner wants the split to see whether they are slowing; a race director wants the elapsed time. Both are recorded, and both are in the export.
Are my laps saved if I reload?
No, and deliberately: a stopwatch that restores an old session when you open it is confusing. Export the CSV before closing if the times matter.