Online Stopwatch

Precise stopwatch with lap recording. Works in the browser, no install needed.

00:00:00.00

How the stopwatch works

The stopwatch uses performance.now() for sub-millisecond precision and updates the display every 10ms via setInterval to show centiseconds accurately.

Elapsed Time
elapsed = performance.now() − startMark
Uses the high-resolution monotonic clock — unaffected by system clock changes or NTP adjustments.
Lap Time
lapTime = currentElapsed − previousLapTotal
Each lap records both the split time and the running total, so you can compare individual lap performance.

When to use a stopwatch

Sports & Fitness

Time running laps, swimming lengths, circuit training sets or rest intervals with lap-by-lap comparison.

Study Sessions

Use the Pomodoro technique — 25 minutes of focused study, 5-minute break — by watching the stopwatch directly.

Presentations

Time your speech or presentation rehearsal and use lap to mark section transitions so you can review timing later.

Frequently asked questions

Is the stopwatch accurate?

Yes. It uses performance.now() which provides microsecond-resolution timing from the browser's monotonic clock. The display updates every 10ms (centiseconds), so the displayed value is accurate to ±10ms.

Does it keep running if I switch tabs?

The timer continues tracking elapsed time even when the tab is in the background, because it uses wall-clock timing rather than counting ticks. The display catches up when you return to the tab.

How many laps can I record?

There is no hard limit on the number of laps. The lap list scrolls vertically. The most recent lap appears at the top for quick reference.

Can I copy the lap times?

You can select the text in the lap list and copy it manually. A dedicated export button may be added in a future update.

What does "Reset" do?

Reset stops the stopwatch (if running), sets the time back to 00:00:00.00, and clears all recorded laps. You can start fresh immediately after resetting.