Stopwatch

Online stopwatch with lap timing. Perfect for workouts, presentations, and sports. This tool processes all data locally in your browser. No information is ever sent to any server. Completely free, no registration required.

How to Use the Stopwatch

1. Enter your input values above
2. Results update automatically
3. Copy or download the output

What is a Stopwatch?

A Stopwatch measures elapsed time with precision down to milliseconds, with lap/split tracking for recording intermediate times. It's used for athletic training (tracking sprint splits, workout intervals), productivity (monitoring how long tasks actually take), presentations (keeping to time limits), science experiments, cooking, and recreational timing. Unlike a countdown timer (which counts toward zero), a stopwatch starts at zero and counts up until stopped — perfect for measuring how long something takes rather than anticipating when something should end.

How Does It Work?

Press Start to begin timing. The stopwatch ticks up from 00:00:00.000 (hours:minutes:seconds.milliseconds), updating every ~10ms for smooth display. Press Lap to record the current time while the stopwatch keeps running — useful for tracking splits in a race or intervals in a workout. Press Stop to pause; Start again to resume. Reset clears all times and starts fresh. All lap times are displayed in a scrollable list, with the fastest and slowest laps highlighted.

Formula

Elapsed = Current Time − Start Time\nLap Time = Current Time − (Start Time + Sum of Previous Laps)\nAverage Lap = Total Time ÷ Number of Laps\nBest Lap = min(Lap Times) | Worst Lap = max(Lap Times)\n\nFormat: HH:MM:SS.mmm\n• 1:23:45.678 = 1 hour, 23 minutes, 45 seconds, 678 milliseconds\n\nPrecision: displays to centiseconds (1/100th second)\nInternal accuracy: ±10-50ms in browser (sufficient for most uses; not for professional timing)

Who Uses This Tool?

• Runners and swimmers tracking lap splits during training
• Public speakers and presenters timing practice runs
• Cooks timing multiple dishes or cooking stages simultaneously
• Students timing exam sections or study intervals
• Productivity experiments: tracking how long tasks actually take

Pro Tips

• For professional athletic timing, use a dedicated stopwatch or timing system — browser-based timers have ±10-50ms variance due to JavaScript's event loop
• Use Lap (not Stop) to record intermediate times without pausing. Laps are numbered sequentially and color-coded: green (fastest), red (slowest)
• Browser timers can drift over very long durations (hours). For short durations (<10 min), accuracy is good enough for fitness and productivity use
• Export lap times as CSV for analysis in spreadsheets or training logs. Great for tracking progress over weeks and months

Frequently Asked Questions about Stopwatch

How accurate is the millisecond display?

The display updates every ~10 milliseconds. However, browser-based timers have inherent ±10-50ms variance due to JavaScript's single-threaded event loop. It's accurate enough for fitness tracking, cooking, and productivity — but not for professional athletic timing.

Does the stopwatch keep running if I switch tabs?

The stopwatch uses the system clock (Date.now()), not a setInterval counter. So if you switch tabs or even close the browser and reopen it (within the same session), the elapsed time will be accurate. The display may pause in background tabs due to browser throttling, but time catches up when you return.

Free online Stopwatch — no signup, 100% client-side processing. All data stays in your browser.