Stopwatch & Timer
Stopwatch with lap tracking, countdown timer with alarm, and an interval timer.
Add intervals below to run a sequence of timed steps back-to-back, or send splits from the Pace Calculator.
00:00.00
The stopwatch uses performance.now() — a high-resolution monotonic clock —
combined with requestAnimationFrame for smooth display updates. Because the
elapsed time is computed as a delta from a reference timestamp (not by summing ticks),
timing stays accurate even when the tab is backgrounded or the frame rate drops.
The countdown timer alarm uses the Web Audio API to synthesize three short beeps directly in the browser — no audio files needed.
The interval timer runs a sequence of timed steps back-to-back: each step counts down, beeps, and auto-advances to the next, so you can time a circuit workout, a set of running splits, or any repeating routine without touching the timer between steps. Add steps by hand, or send a splits sequence straight from the Pace Calculator.
How accurate is the stopwatch?
The stopwatch uses performance.now(), a high-resolution monotonic clock accurate to sub-millisecond precision. Displayed time is computed as a delta from a reference timestamp, not by summing ticks — so accuracy is maintained even if the tab is backgrounded or the frame rate drops.
Will the countdown timer alarm play if the tab is in the background?
Most browsers throttle or suspend JavaScript timers in background tabs, which can delay the alarm trigger. Keep the tab visible or prevent your browser from suspending it. The timer continues counting (the reference timestamp is preserved), but the alarm may fire a few seconds late.
Can I run the stopwatch and timer at the same time?
Yes — both run independently on the same page. Start the timer, then start the stopwatch; they use separate animation loops and do not interfere with each other.
What is the interval timer for?
The interval timer runs a list of timed steps one after another — each counts down, beeps, and automatically starts the next. It is useful for circuit or HIIT workouts, running splits, cooking stages, or any routine with several timed segments. Use Skip to jump to the next step, or Pause to hold the current one.
How do I load running splits into the interval timer?
Open the Pace Calculator, enter your distance and pace (or time), and click "Send to timer" above the splits table. Each split segment becomes an interval step, so the timer beeps as you reach each checkpoint at your target pace.