How this stopwatch keeps accurate time
A naive stopwatch counts ticks: every hundredth of a second it adds one hundredth to a running total. That approach falls apart in a browser, because browsers deliberately slow timers down in background tabs to save battery, and even in a foreground tab a busy page can delay a tick by several milliseconds. The errors are tiny individually and enormous in aggregate.
This stopwatch never counts ticks. When you press Start it records the exact moment on your browser's high-resolution monotonic clock (performance.now, which measures in fractions of a millisecond and never jumps, even if the system clock changes). Every screen update then recomputes the elapsed time from that original timestamp. If the display freezes because the tab is in the background, nothing is lost: the moment the tab wakes up, the subtraction gives the true elapsed time, including everything that happened while you were away.
Stop banks the time recorded so far; Start resumes from the same total; Reset clears everything, including the lap list. The display shows minutes, seconds and hundredths, and the minutes column simply keeps growing for long sessions, so an hour and a half reads as 90:00.00.
Splits and totals explained
Press Lap while the clock runs and a row is added showing two numbers. The total is the time on the clock at the moment you pressed Lap, measured from the very start. The split is how long that individual lap took on its own, which is just that lap's total minus the previous lap's total. The newest lap sits at the top of the list.
What people actually time
Runners are the classic users: splits show instantly whether each lap of the track is holding pace or drifting, and the total keeps the whole session honest. But the same two columns work for anything repetitive. Time each question in a practice exam paper to find out where the minutes really go. Time each step of a recipe you are trying to speed up. Time how long the standing items in your weekly meeting take, and enjoy the awkward silence when you share the results.
For focused work sessions a countdown usually beats a count-up, because a visible deadline changes behaviour in a way an open-ended clock does not. If that is what you are after, the Pomodoro timer runs 25 minute sessions with proper breaks, and the hours calculator turns a start and end time into hours worked after the fact.
An honest note on precision
The clock behind this page is precise to well under a millisecond, but a hand-operated stopwatch is only as sharp as the hand operating it. Human reaction time is roughly 0.2 seconds, and it applies twice, once at the start and once at the stop, sometimes cancelling out and sometimes stacking. That is why athletics distinguishes hand timing from fully automatic timing, and why official records require the latter. For school sports day, the kitchen and the office, hundredths are plenty. Nothing you time here is stored or sent anywhere; refreshing the page clears the clock and the laps.
Frequently asked questions
How accurate is this stopwatch?
It uses your browser's high-resolution clock (performance.now), which measures in fractions of a millisecond, and the display shows hundredths of a second. In practice the limit is you, not the tool: human reaction time is around two tenths of a second, so any hand-operated stopwatch carries that margin on both the start and the stop.
Does it keep time if I switch tabs?
Yes. The stopwatch records the moment you pressed Start and works the elapsed time out from that timestamp whenever it updates, rather than counting ticks. Browsers slow background tabs down, which can freeze the display, but the moment you come back the correct time is shown, including everything that passed while you were away.
What is the difference between split and total?
Total is the time on the clock when you pressed Lap, measured from the very start. Split is how long that individual lap took, which is simply that lap's total minus the previous lap's total. Runners use splits to see whether each lap is faster or slower than the last.
Is there a limit to how long it can run?
No practical one. The minutes column simply keeps growing, so an hour and a half shows as 90 minutes and change. If you close the tab the stopwatch stops, though, so for timing across days you may prefer noting start and end times and using the hours calculator.
Are my times stored anywhere?
No. Everything runs in your browser and nothing is sent to any server. Refreshing or closing the page clears the clock and the lap list, so copy any times you want to keep before you leave.