Does this stopwatch keep running if I switch tabs?

Yes. It reads the real clock rather than counting ticks, so background throttling cannot make it drift. Switching tabs or locking the screen does not affect the elapsed time.

How accurate is an online stopwatch?

This one is accurate to the millisecond because it measures against the system clock. Your reaction time pressing the button is a far larger source of error than the timer.

What is the difference between a lap and a split?

A lap is the time since the previous lap. A split is the total elapsed at that moment. Both are shown here, since people use the words interchangeably.

Online stopwatch

Start, lap, stop. Keeps time correctly even in a background tab.

Runs in your browser. Nothing is sent, saved, or shared.

00:00.00

Space to start or pause, L for a lap

Laps

No laps yet. A lap is the time since the previous one; the total is the elapsed time at that point.

Why browser stopwatches usually drift

Most are built by adding ten milliseconds to a counter on a repeating interval. Browsers throttle those intervals hard in a background tab, often to once a second or once a minute, so the count falls behind the moment you switch away.

This one records the wall-clock instant you pressed start and subtracts it from the current time. The display refresh rate has no bearing on the elapsed value, so a tab that was hidden for ten minutes comes back showing exactly ten more minutes.

Laps and splits are different things

A lap is the time since the previous lap. A split is the total elapsed at that point. Both are shown, because people mean different things by lap and reading the wrong column is how a session gets logged wrong.

For intervals, the lap column is the one you want. For a race split, the total is.

How to use the stopwatch

1
Press start
Or hit the space bar, which is faster when your hands are already on the keyboard.
2
Record laps
Each lap shows both the time since the last lap and the total elapsed.
3
Pause or reset
Pausing holds the elapsed time. Reset clears it and the lap list.

Questions people ask

Does this stopwatch keep running if I switch tabs?: Yes. It reads the real clock rather than counting ticks, so background throttling cannot make it drift. Switching tabs or locking the screen does not affect the elapsed time.
How accurate is an online stopwatch?: This one is accurate to the millisecond because it measures against the system clock. Your reaction time pressing the button is a far larger source of error than the timer.
What is the difference between a lap and a split?: A lap is the time since the previous lap. A split is the total elapsed at that moment. Both are shown here, since people use the words interchangeably.