Stopwatch

What this tool does

Stopwatch provides precise start/stop/reset timing with millisecond precision using a high-resolution clock, plus lap recording that shows both each lap’s own split duration and the cumulative total time at that point.

A basic timer is easy to find, but one with accurate lap splitting, showing both each individual lap’s duration and the running cumulative total, needs a bit more than a simple start/stop button.

This stopwatch uses performance.now(), a high-resolution browser clock unaffected by rendering load, for accurate timing, with a Lap button that records a split at any point while running.

How to use Stopwatch

1. Press Start to begin timing.
2. Press Lap at any point to record a split.
3. Press Stop to pause, or Reset to clear everything and start over.
4. Press Start again at any time to resume from where you paused.

Tips for better results

• Each recorded lap shows two numbers: its own individual split duration (just that lap’s length) and the total cumulative time elapsed at that point, useful for comparing lap-to-lap pacing.
• Timing uses performance.now() rather than setInterval alone, which keeps it accurate even if the browser tab is doing other work in the background.
• Laps are listed most-recent-first, the newest lap appears at the top of the list as you record more.
• Resetting clears both the elapsed time and the full lap history, there’s no way to recover a cleared lap list, so note down any splits you need before resetting.

Common use cases

• Timing a workout, run, or any physical activity with lap splits.
• Measuring how long individual steps of a task take, one lap per step.
• Timing a presentation or speech rehearsal to check its overall length.
• Comparing pacing across multiple repeated attempts at a timed task.

Common mistakes to avoid

• Confusing a lap’s individual split duration with the cumulative total shown alongside it, both numbers are shown per lap specifically to avoid this ambiguity, read the smaller split number for "how long was just this lap."
• Resetting before noting down needed lap times, since reset clears the full lap history with no way to recover it afterward.
• Expecting the stopwatch to keep running accurately if the device goes to sleep or the browser is fully closed, browser timers generally pause under those conditions; keep the device awake for an uninterrupted timing session.