Math & Everyday
Stopwatch & Timer
A precise stopwatch with laps, plus a countdown timer.
🔒 Runs entirely in your browser — nothing here is ever uploaded
CalcoTools · Stopwatch & Timer · generated 8/23/2026, 1:04:40 PM
About the Stopwatch & Timer
A precise browser-based stopwatch with lap tracking, plus a separate countdown timer — both running entirely client-side.
How to use it
- Switch between the Stopwatch and Countdown Timer tabs.
- Stopwatch: press Start, use Lap to record splits, and Reset to clear.
- Timer: enter Minutes and Seconds, then press Start.
Formula
Stopwatch elapsed time updates every 10 milliseconds using your browser's interval timer. Countdown decrements once per second from the entered duration.
Worked example
Setting a 5-minute countdown timer counts down from 05:00 to 00:00, then displays a completion state.
Recommendations
- • Browser tabs can slightly throttle timers when inactive in the background — keep the tab active for critical timing.
- • The stopwatch's lap feature keeps a running list of split times without resetting the main clock.
- • Use the countdown timer for cooking or workout intervals, and the stopwatch for open-ended timing like a workout session length.
Frequently asked questions
It updates in 10-millisecond increments using your browser's timer — accurate enough for everyday timing, though not built for scientific-grade precision.