Stopwatch
A precise online stopwatch with lap times. Start, pause and resume without losing accuracy, record up to 50 laps, and read hundredths of a second on a steady tabular display.
Reviewed by the CalcCafe editorial team · Last updated 18 July 2026 · How we test our tools
Example
Timing interval sprints at the track: press Start as the runner leaves the line, tap Lap each time they pass you, and Pause when the set ends. If they cross at 1:23.45, that is 1 minute, 23 seconds and 45 hundredths. The lap list keeps every split in order, so after four 400 m repeats you can read all four times back without scribbling anything down. Press Start again to resume exactly where you paused — the elapsed time is recomputed from the clock, so nothing is lost — and Reset clears the display and the laps for the next athlete.
How it works
When you press Start, the stopwatch records a reference timestamp (the current time minus any elapsed time already on the clock). It then refreshes the display about 20 times per second, each time computing elapsed = now − reference. Because the elapsed figure is always derived from the system clock rather than by adding up timer ticks, jitter in the refresh interval and pause/resume cycles never accumulate error. Lap stores the current reading in a list (up to 50 entries) without stopping the clock; Reset clears both the time and the laps.
Good to know
The display shows minutes, seconds and hundredths of a second (centiseconds) — the same resolution as a classic handheld sports stopwatch. Hundredths are a sensible limit for a browser tool: human reaction time when pressing a button is around 150–250 ms, so finer digits would imply a precision your thumb cannot deliver. For hand-timed events, treat results as accurate to roughly a tenth of a second.
There is a design detail worth knowing: JavaScript's setInterval is not metronome-accurate — the browser may fire it a few milliseconds late, or much later in a busy or backgrounded tab. A naive stopwatch that adds a fixed amount per tick would drift badly. This one never counts ticks; every refresh recomputes the elapsed time as the difference between the current clock time and the moment you pressed Start. The interval only controls how often the display repaints, so even if ticks arrive late, the time shown is still correct.
Lap and split are different measurements. A lap time is the duration of one segment (this circuit took 1:58.30), while a split is the cumulative time from the start (the runner passed 800 m at 4:02.11). This stopwatch records cumulative splits, which is what you want for race checkpoints; subtract consecutive entries to get individual lap durations.
Typical uses: interval workouts and circuit training, timing rests between sets, steeping tea or timing a boiling egg, speedcubing practice, board-game turns, and rough benchmarking of anything you can see start and finish. One caveat applies to all browser timers: inactive tabs are throttled to save power. The math here means the total stays correct when you come back, but the display will only catch up once the tab is visible again — so keep the tab in view if you need to watch the digits live.
Frequently asked questions
How accurate is this online stopwatch?
The elapsed time is computed from your device's system clock as the difference between now and the moment you pressed Start, so it is as accurate as that clock - typically within milliseconds. The practical limit is your reaction time pressing the buttons, around 0.15-0.25 seconds.
What is the difference between a lap and a split?
A lap time measures one segment on its own; a split is the cumulative time from the start. This stopwatch records cumulative splits when you press Lap - subtract consecutive entries to get individual lap durations.
Is my data uploaded anywhere?
No - this stopwatch runs entirely in your browser and keeps working offline once the page has loaded. Times and laps stay on your device and disappear when you leave the page.
Does the stopwatch keep running if I switch tabs?
Yes. Browsers throttle the display refresh in background tabs, but the elapsed time is recomputed from the clock, so when you return the total is still correct - the digits simply jump forward to the right value.
People also ask
What does the .45 in 1:23.45 mean?
The digits after the dot are hundredths of a second (centiseconds). 1:23.45 means 1 minute, 23 seconds and 45 hundredths - i.e. 83.45 seconds in total.
Can I pause and resume without losing time?
Yes. Pause freezes the reading, and Start resumes from exactly that point by shifting the reference timestamp, so pausing never adds or loses time no matter how long the stopwatch sits paused.
How many laps can I record?
Up to 50 laps are kept in the scrolling list. That covers most workouts and races; press Reset to clear the list and start a fresh session.
How long is 999 hours on a stopwatch?
999 hours is 41 days and 15 hours (999 / 24 = 41.625 days), or 59,940 minutes. The figure comes up because some handheld digital stopwatches have a display limit, such as 99 or 999 hours, after which they stop or roll over. This stopwatch shows minutes, seconds and hundredths, and because it computes elapsed time from the system clock rather than by counting ticks, it stays accurate however long it runs.
Does a stopwatch drain your battery?
A dedicated handheld stopwatch uses so little power that a single coin cell typically lasts for years. A stopwatch running in a web browser costs more, mainly because the screen stays on and the display refreshes about 20 times per second, but that is still a light load compared with video or games. If you are timing something long, dim the screen or plug in; the timing itself keeps working because elapsed time is recomputed from the clock, not from constant screen updates.
What is a 1/100 stopwatch?
A 1/100 stopwatch displays time to the hundredth of a second, so 1:23.45 means 1 minute, 23 seconds and 45 hundredths. This is the standard resolution for sports stopwatches and is what this online stopwatch shows. Some lab and professional timers go to thousandths (1/1000), but for hand-operated timing the extra digit is not meaningful because human reaction time is around 150 to 250 milliseconds.
Is it possible to get .01 on a stopwatch?
Yes, the display can show 0.01 seconds, but you cannot reliably stop a stopwatch on a chosen hundredth on purpose. Pressing a button takes roughly 150 to 250 milliseconds of reaction time, so landing on exactly .01 elapsed, or on any specific hundredth, is a matter of chance rather than skill. That is why hand-timed results should be treated as accurate to about a tenth of a second even though two decimal places are shown.
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Sources & references
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