Lap time and split time
These are different measurements and the distinction matters when reading results.
- Lap time is the duration of one segment on its own — how long that lap took.
- Split time is the total elapsed at the moment the lap was recorded — cumulative from the start.
| Lap | Lap time | Split time |
|---|---|---|
| 1 | 1:02.40 | 1:02.40 |
| 2 | 0:58.90 | 2:01.30 |
| 3 | 1:01.20 | 3:02.50 |
| 4 | 0:57.80 | 4:00.30 |
This stopwatch records both. Lap 4 was the fastest at 57.80 seconds, and the total run took 4:00.30 — a negative split, since the second half was faster than the first.
Precision and drift
This stopwatch uses performance.now(), a monotonic high-resolution clock that is unaffected by system time changes, and displays to a hundredth of a second.
It stores the start timestamp and computes elapsed time on every frame rather than incrementing a counter. A counter-based timer drifts by seconds over a long run, because browsers throttle background tabs and each tick carries rounding error. Reading the clock instead means the elapsed time is always correct.
For anything officially timed, electronic timing gates are used precisely because the human at the button is the largest source of error, not the clock.
Frequently asked questions
Does the stopwatch keep running if I switch tabs?
Yes. It reads the elapsed time from a monotonic clock rather than counting ticks, so background throttling does not affect accuracy.
The display catches up the moment you return to the tab.
What is the difference between lap and split time?
Lap time is how long one segment took on its own. Split time is the cumulative total at the moment the lap was recorded.
This stopwatch shows both columns.
How accurate is it?
Display precision is a hundredth of a second, and the underlying clock is far finer. In practice the limit is human reaction time at the button — around 200 milliseconds.
For anything official, electronic timing gates remove the human from the loop entirely.
Are there keyboard shortcuts?
Yes. Space starts and stops, L records a lap, and R resets.
They work anywhere on the page, provided you are not typing in a text field.