Online Stopwatch
A precise online stopwatch that reads to the millisecond, records unlimited laps with both lap and split times, and keeps counting even if you reload the page.
How to use Online Stopwatch
- Press Start, or tap the space bar, to begin timing from zero.
- Press Lap (or the L key) each time you want to mark a split — the table records both the individual lap and the cumulative time.
- Pause and resume as often as you need; the elapsed total carries across.
- Download the lap table as a CSV file to keep or analyse in a spreadsheet.
- Press Reset (or R) to clear the clock and start a fresh set of laps.
About Online Stopwatch
Most people reach for an online stopwatch because the physical one is in a drawer somewhere: timing an interval session, a presentation rehearsal, a chemistry experiment, a support call, or how long a build actually takes. What they need is a big readable clock, a lap button that does not require aiming, and a record they can keep afterwards. That is exactly what this page is — no ads over the buttons, no sign-up, and nothing sent anywhere.
Under the surface it is built on performance.now(), the browser's monotonic high-resolution timer. Unlike Date.now(), it cannot jump backwards when the operating system syncs its clock, and it is unaffected by daylight saving. Elapsed time is always recomputed from the start timestamp plus any accumulated paused segments, so the reading is exact regardless of how often the display repaints — an important difference from stopwatches that add sixteen milliseconds per frame and quietly drift by seconds over a long session.
The lap table is the part people keep coming back for. Each row shows the lap time and the running split, the fastest and slowest laps are highlighted so pacing problems are visible at a glance, and the whole table exports to CSV for a spreadsheet. Because the running state is written to local storage as you go, an accidental reload — or a browser crash — does not cost you the session: reopen the page and the clock is still running, at exactly the right time.
Frequently asked questions
How accurate is this online stopwatch?
Timing uses performance.now(), a monotonic high-resolution clock that is immune to system clock changes, and the display refreshes on every animation frame. Practical accuracy is limited by human reaction time on the start and stop presses — roughly 150–250 milliseconds — not by the stopwatch, which is accurate to well under a millisecond.
Does it keep timing in a background tab?
Yes. Elapsed time is derived from timestamps rather than counted up frame by frame, so switching tabs or minimising the window cannot make it lose time. The digits stop repainting while the tab is hidden and jump to the correct value the moment you come back.
What happens if I reload the page by accident?
Nothing is lost. The start timestamp, the accumulated time and every recorded lap are saved in your browser as you go, so a refresh — or even closing and reopening the tab — restores a running stopwatch at the correct elapsed time.
What is the difference between a lap and a split?
A lap is the time since the previous lap marker; a split is the total elapsed time at that marker. A runner doing four circuits sees four lap times that describe each circuit and four splits that describe cumulative race progress. Both are shown for every row, and the fastest and slowest laps are highlighted automatically.
Can I export the lap times?
Yes. The whole table downloads as a CSV with lap number, lap time, split time and both values in raw milliseconds, so you can chart it in a spreadsheet. You can also copy the table as plain text in one click.
Are there keyboard shortcuts?
Space starts and stops, L records a lap, and R resets. Shortcuts are ignored while you are typing in a field, so they never interfere with the rest of the page.
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