Stopwatch
Last updated: 23 October 2026
Time anything to the centisecond with lap splits you can copy in one click — timestamp-based, so it stays accurate even in a background tab.
00:00.00
Why this tool is private
Your numbers are crunched locally in this tab — nothing is sent to a server. No sign-up, no uploads, nothing to install.
How to use the Stopwatch
- Press Start to begin timing. The display shows total minutes, seconds and centiseconds — it keeps counting past 59 minutes rather than rolling into hours.
- Press Lap while the stopwatch is running to record a split. Each new row shows the lap number, that lap's own time, and the total time so far.
- Press Pause to freeze the elapsed time; press Resume to continue from exactly the stored figure — paused time is never counted.
- When laps exist, use the Copy laps button to copy the full list as plain text lines, ready to paste into notes or a spreadsheet.
- Press Reset to return the display to 00:00.00, clear every lap, and start again from a clean slate.
About this Stopwatch
This online stopwatch times anything to the centisecond and records laps as you go: each lap row shows the lap's own duration and the total elapsed time, and the Copy laps button turns the whole list into plain text lines you can paste into a training log, notes app or spreadsheet. Because the elapsed time is derived from timestamps on your device clock rather than counted screen refreshes, it stays accurate even if the tab sits in the background. Minutes are shown as a running total with no hours rollover, so a 75-minute effort reads plainly as 75:00.00.
How this stopwatch measures time
A naive stopwatch adds a small amount to its total every time the screen updates — and drifts whenever the browser slows those updates down, which browsers deliberately do in background tabs. This one never counts updates. When you press Start it records a timestamp; the elapsed time you see is always 'now minus then', recomputed from your device's clock about 40 times a second. Pause banks the elapsed time so far, Resume starts a new timestamp segment, and the total is the sum of the segments — which is why paused minutes never leak into your result.
The display format is minutes, seconds and centiseconds (hundredths of a second): 01:23.45 means one minute, twenty-three seconds and forty-five hundredths. Minutes are total minutes with no hours rollover — a 75-minute run reads 75:00.00, not 1:15:00 — which keeps long timings unambiguous when you copy them. The centiseconds come from the millisecond precision of the device clock, refreshed fast enough to look continuous.
Worked example: timing a set of swim intervals
A swimmer wants to check pacing across four 100-metre repeats. She starts the stopwatch as she pushes off, and presses Lap at each wall touch. The list builds: Lap 1 — 01:32.10 — 01:32.10; Lap 2 — 01:35.44 — 03:07.54; Lap 3 — 01:31.02 — 04:38.56; Lap 4 — 01:29.87 — 06:08.43. The first number in each row is that repeat on its own, the second is the running total — so she can see instantly that repeat two was the slow one and the set finished faster than it started.
Afterwards she taps Copy laps and pastes the four lines straight into her training notes, dates and all her own commentary added around them. The same flow works wherever splits matter: laps of a running track, stages of a recipe where each step's duration matters, segments of a presentation rehearsal, or how long each stage of a board-game turn takes. If a lap press is missed, the totals still anchor the timing — the next lap simply covers two segments.
Reading laps well: splits, totals and pacing
The lap time and the total answer different questions. The total tells you where you are against the clock — useful in a race or a timed test. The lap time tells you how each segment compared with the others, which is where consistency shows: distance runners look for even splits or a slight negative split (second half faster than the first), and a lap that suddenly balloons usually marks exactly where concentration, traffic or fatigue got in. Comparing lap times within one session is more informative than comparing totals across sessions, because each lap is self-contained.
A practical habit: take laps at fixed, meaningful boundaries — every circuit, every page, every exercise — rather than at random moments, and copy the list before you reset. A page of unsaved laps vanishes the moment Reset is pressed. If you need to time several people or attempts in sequence, run them one at a time and copy each set of laps into your notes before starting the next; the stopwatch holds one session at a time, cleanly.
Honest limitations
Centisecond figures look laboratory-precise, but the real precision of hand timing is set by the human pressing the button: reaction time to a start signal or a finish is typically around a fifth of a second, far larger than the hundredths on screen. Treat the last digits as exact arithmetic on your presses, not as proof of the exact moment something happened. The timing basis is your device's clock, so a device whose clock is mis-set or being adjusted can shift results.
There is also no memory here by design: laps are not saved anywhere, closing or reloading the page wipes the session, and there are no accounts, history, averages or charts. The stopwatch also cannot time in your pocket with the screen locked for long stretches in every browser — mobile browsers may freeze the page, though on return the timestamp maths shows the correct elapsed time. For one clean timing with honest splits you can paste anywhere, it does the whole job; for permanent records, copy the laps into your own notes.
How it works
Press Start and this online stopwatch times to the centisecond, counting total minutes so runs over an hour just keep going. Press Lap while it runs to record each split with its own lap time and the total time, then copy the whole lap list as plain text in one click. The elapsed time is calculated from timestamps on your own device clock, not by counting screen refreshes, so it does not drift when the tab is in the background. It all runs in your browser — nothing is uploaded, and no sign-up is needed.
Privacy note: this tool runs locally in your browser. Your input is not uploaded, stored in analytics, or placed in the page URL.
Frequently asked questions
How do laps work — what do the two times in each row mean?
Each press of Lap does two things. It records the time since the previous lap — that lap's own duration — and the total elapsed time at that moment, and both appear in the lap row underneath the display, numbered in the order you recorded them. The stopwatch itself keeps running; a lap is a marker, not a pause. You can record as many laps as you need, and the Copy laps button copies the whole list as plain text.
How accurate is this stopwatch?
The elapsed time is not counted by adding up screen refreshes. The stopwatch stores the timestamp of when you pressed Start (and banks the elapsed time whenever you pause), then calculates the time shown by subtracting those timestamps from the current time — so it is as accurate as your device's clock. The display refreshes about 40 times a second, but even if a background tab refreshes less often, the figure is correct when you return.
What is the maximum time it can measure?
There is no built-in cut-off. The display counts total minutes, seconds and centiseconds — it does not roll over into hours, so after an hour it simply reads 61:23.45 and keeps going, past 100 minutes and beyond, until you press Pause or Reset or close the tab. In practice the limits are your battery and your patience, not the tool; for multi-day timing you would also want to copy any laps you care about before resetting.
Does it keep timing accurately in a background tab?
Yes. Because the elapsed time is worked out from timestamps rather than counted refresh by refresh, switching tabs cannot make it lose or gain time. The display itself may update less frequently while the tab is in the background — browsers ration that work — but the moment you come back it shows the correct elapsed time, and laps you take after returning are timed from the true timestamps too.
What format does Copy laps produce?
As numbered plain-text lines, one per lap, in the order you recorded them — for example 'Lap 2 — 01:05.20 — 02:11.87'. The first time is that lap alone, the second is the total when the lap was taken. Paste them anywhere text goes: a notes app, a training log, a message, or down a spreadsheet column. Copying needs laps to exist — press Lap at least once while the stopwatch is running and the Copy laps button appears.
What is the difference between this and the Countdown Timer?
This stopwatch only counts up. It starts at zero, times how long something takes, and lets you mark laps along the way. The Countdown Timer on this site does the opposite job: you set a length in advance — hours, minutes and seconds — and it counts down to zero and beeps when the time is up. Use the stopwatch when you do not know how long something will take; use the countdown when the length is fixed in advance.
Is anything stored or uploaded while I use it?
Yes. Everything happens in this browser tab: the timing, the lap list and the copying are all done locally, nothing is sent to a server, and no account or install is needed. The flip side is that nothing is saved either — your laps exist only on this page, so copy them before pressing Reset or closing the tab if you want to keep them. Reloading the page clears the stopwatch completely.
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