Stopwatch
A stopwatch with laps that does not drift in a background tab.
Ready
00:00.00
Settings
Nothing to configure. Start, stop and resume as often as you like; the elapsed total is measured against the clock, so stopping and resuming does not lose time.
Clocks here run against real time, so a background tab does not make them drift. Browsers do hold audio in inactive tabs, so a sound may arrive late even when the time is right.
How this calculation works
Elapsed time is the difference between two readings of the system clock, not a running total of interval callbacks. That distinction matters more than it sounds: a stopwatch that accumulates from timer callbacks loses time whenever the machine is busy, and browsers throttle timers hard in a background tab, so a counting stopwatch can be minutes short after an hour out of view. This one simply subtracts, so backgrounding the tab pauses the display and never the measurement.
What the results mean
- Elapsed
- Total running time. Stopping and resuming adds to the total rather than restarting it, so a session can be paused without losing anything.
- Lap
- The time since the previous lap, not since the start. The split from the beginning is the running total shown above.
- Average lap
- Useful for pacing. A rising trend across laps is usually more informative than any single one.
Common problems and fixes
- The display freezes when I switch tabs
- That is the browser suspending animation in a hidden tab, and it affects the display only. The elapsed time is computed from the clock when you come back, so the figure is correct even though nothing was drawn while you were away. If you need to watch it continuously, open the tab in its own window and keep it visible.
- Laps are lost after a refresh
- Nothing is stored, by design, so a refresh clears the session. Copy the times out before reloading if you need them. For anything you must keep, write the figures down as you go rather than relying on a browser tab surviving.
Frequently asked questions
How accurate is a browser stopwatch?
The underlying clock is accurate to well under a millisecond, but browsers deliberately coarsen timing to defend against side-channel attacks, and the display only updates when the browser paints. The practical limit is your own reaction time on the buttons, which is 150 to 250 milliseconds for most people.
Does it keep running if I close the tab?
No. Closing the tab ends the page and everything with it. Switching tabs or minimising the window is fine, since the elapsed time comes from the clock rather than from anything that has to keep running.
What is the difference between a lap and a split?
A lap is the time since the previous lap mark. A split is the total elapsed at that moment. The laps listed here are lap times, and the large figure at the top is the split.
Put this on your own site
Free to embed, no attribution required beyond the source link the frame carries itself. It runs entirely in your visitor's browser, sets no cookies and loads no third-party script.
<iframe src="https://runthetests.com/embed/stopwatch/" width="100%" height="560" style="border:1px solid #e5e5e5;border-radius:8px" title="Stopwatch" loading="lazy"></iframe>
Preview it at https://runthetests.com/embed/stopwatch/. Embedded pages are marked noindex, so yours stays the canonical copy — not this one.