Stopwatch

Start, lap, stop

Press Start and it counts up. Press Lap to mark a segment without stopping the clock. Stop when you are done, and the table has every lap with both its own time and the running total.

Everything runs in your browser, and the times are yours — nothing is uploaded, and nothing is kept when you leave.

Laps and splits are different things

The distinction is worth knowing because coaches, race timers and running watches all use both, and they mean opposite things.

A lap is the time for that segment on its own — how long the third lap took.
A split is the total elapsed at the moment you pressed the button — how long you had been going when the third lap ended.

Both columns are shown, labeled “this lap” and “total time”, because which one you want depends entirely on the question. Lap times tell you whether you are slowing down. Splits tell you whether you are on pace.

A worked example. Four 400-metre laps at 90, 92, 95 and 88 seconds gives splits of 1:30, 3:02, 4:37 and 6:05. The laps say the third was the hard one and the fourth was a kick; the splits say the whole thing took just over six minutes. Neither number contains the other’s information.

Why the times are stored the way they are

The stopwatch records cumulative times when you press Lap, and works out each lap by subtracting the one before it.

Doing it the other way — recording each lap’s own duration and adding them for the total — seems equivalent and is not. Each measurement carries a small rounding, and adding a dozen of them lets the sum drift away from what the clock says. A stopwatch whose lap times do not add up to its own reading is broken, whatever else it gets right.

Subtracting from cumulative marks means the last lap’s total is always exactly the reading on the clock, by construction.

Tenths, and why not hundredths

The display stops at a tenth of a second. That is the honest limit for this, for two reasons.

A browser cannot promise better. It shares a thread with the rest of the page, and under load — a heavy site in another tab, a phone thermally throttling — the gap between updates stretches. The underlying number is more precise than the display, but reporting hundredths would imply a repeatability that is not there.

More to the point, you cannot press a button that accurately. Simple visual reaction time is around 200 to 250 milliseconds for most people, and even an expert timekeeper anticipating a finish is working in tenths. This is why hand timing at athletics meets is recorded to a tenth and only electronic timing to a hundredth.

Two extra digits that measure nothing but your reflexes are not extra precision.

It does not lose time when you look away

Most browser stopwatches count upward once a second and add as they go. That works while you are watching, and fails the moment you are not.

Browsers deliberately throttle pages in background tabs to save battery — to once a second, then to once a minute, and on a locked phone often to nothing at all. A stopwatch built by counting simply stops counting, and the total that comes back is however much of the elapsed time the browser happened to allow.

This one reads the clock instead. The total is the difference between now and when you started, minus any time you had it paused, so a hidden tab or a sleeping screen costs exactly nothing. Look back after an hour and the number is right.

The one thing that does stop it is closing the tab. Nothing here runs on a server.

Getting the numbers out

The copy button puts the total and every lap on the clipboard as tab-separated text — lap number, lap time, total time. That pastes into a spreadsheet as three proper columns rather than one, which is the difference between having data and having to retype it.

Laps are deliberately not put in the page address, unlike the settings on the other timers here. A list of split times is a record of something you did, and a shareable link is the wrong place for it. Copy them out if you want to keep them; reloading the page clears them.

What it is good for

Intervals and repeats, where the lap button is the whole point. Timing how long a task actually takes, which is almost never what you estimated. Cooking steps. Timing a speech or a presentation run-through. Anything where you want to measure a duration rather than count down to the end of one.

To count down to zero instead, with an alarm, use the countdown timer. For repeated work blocks with breaks between them, the pomodoro timer handles the cycle.

Using it with a screen reader

A reading that changes twenty times a second cannot be announced — a live region doing that would make the page unusable. So the clock is silent and readable on demand, and the tool speaks only when the state changes: “stopwatch running”, and on stopping, the total spelled out in words rather than as a clock face.

Lap rows are a real table with real headers, so each cell is announced with what it means rather than as a stream of unlabeled numbers, and the fastest and slowest laps are named in text rather than only tinted.

Frequently asked questions

What is the difference between a lap and a split?

A lap is the time for that segment alone; a split is the total elapsed when you took it. The table shows both — "this lap" and "total time" — because runners and swimmers use them for different things.

Does it keep time if I switch tabs or lock the phone?

Yes. The total is read from the clock rather than counted up, so a hidden tab or a sleeping screen costs nothing — the number is correct the moment you look again. Closing the tab does stop it.

Why only tenths of a second?

Because that is the honest limit. A browser cannot promise better under load, and the delay between seeing something and pressing a button is a tenth of a second at best. Showing hundredths would be adding digits the measurement cannot support.

Can I copy the lap times out?

Yes — the copy button in the header puts the total and every lap on the clipboard as tab-separated text, which pastes straight into a spreadsheet as columns.

Are my laps saved?

No. They live in the page and disappear when you reload or close it, and they are deliberately kept out of the page address — a list of split times is not something to put in a shareable link. Copy them out if you need them.

Which lap was fastest?

The fastest is highlighted and both the fastest and slowest are labeled, once there is more than one lap to compare. With a single lap there is nothing to be fastest than.