Online Stopwatch with Laps - Accurate in a Background Tab, No Signup
Press Start and the stopwatch counts in hundredths of a second. Take laps to see each lap time and the running total, with the fastest and slowest lap marked, then copy the laps as text or CSV.
Maintained by Hirantha Sandaruwan Lakshan. Updated 15 October 2026.
About this tool
The time is worked out from your device's clock every time the screen is redrawn, so it stays correct when you switch tabs or the device sleeps. Nothing is saved or sent anywhere.
How it works
A stopwatch that counts timer ticks drifts, because browsers delay timers in tabs you are not looking at. Chrome, for example, can check the chained timers of a tab that has been hidden for more than five minutes, and silent for 30 seconds, only once a minute (Chrome for Developers, checked 2026-10-15). This stopwatch never counts ticks. When you press Start it notes the clock reading, and when you stop it adds the time since that reading to the time it had already counted. The number on screen is always the time already counted plus the time since the last Start, so a late redraw only means a late refresh, never a wrong answer.
The display is redrawn with requestAnimationFrame, which browsers pause in a background tab to save battery (MDN, checked 2026-10-15). When you come back, the next frame reads the clock and shows the correct time at once. The clock is Date.now(), whole milliseconds since 1 January 1970 UTC. Browsers can reduce its precision for privacy: MDN notes that Firefox with resist fingerprinting switched on rounds to about 16.7 ms. The display shows hundredths of a second, rounded down. The trade-off of using the device clock is that it keeps counting while the device sleeps, which is what you want when timing a task, but changing the system clock while the stopwatch runs would change the reading.
A lap is the time since the previous lap, shown with the total on the stopwatch when you pressed Lap. With two or more laps that are not all equal, the shortest lap is marked Fastest and the longest Slowest, in words as well as colour, and a tie goes to the earlier lap. The table keeps up to 999 laps, newest first. Copy gives plain text or CSV, with each time in clock form and in plain seconds so that a spreadsheet can add the seconds up.
Space starts and stops, L takes a lap and R resets. The shortcuts are ignored while you hold Ctrl, Alt or Command, while you type in a field, and for Space when a button or link has the focus, so they do not get in the way of the rest of the page. You can switch them off. A screen reader is not told the time on every frame; it gets a short polite announcement when you start, stop, take a lap or reset. Nothing is stored: closing or reloading the page clears the time and the laps.
Worked examples
Timing laps of a run
Laps taken at 01:18.12, 02:34.57 and 03:54.37 on the stopwatch give lap times of 01:18.12, 01:16.45 and 01:19.80 (154.57 - 78.12 = 76.45, and 234.37 - 154.57 = 79.80). Lap 2 is marked Fastest and lap 3 Slowest. The average lap is 01:18.12, because 234.37 divided by 3 is 78.12.
A long task with the screen locked
Start at 09:00:00, lock the screen, and look again 1 hour 20 minutes and 34.56 seconds later. The stopwatch reads 1:20:34.56, which is 4,834.56 seconds. It does not matter that nothing was drawn in between, because the reading comes from the clock.
Copying laps into a spreadsheet
Copy as CSV gives a header row, Lap,Lap time,Total time,Lap seconds,Total seconds, and then one row per lap, such as 2,01:16.45,02:34.57,76.45,154.57. The two seconds columns are plain numbers.
Frequently asked questions
Does the stopwatch keep the right time when I switch tabs or lock my phone?
Yes. It stores when you pressed Start and reads your device's clock each time it draws, so time that passes while the tab is hidden is counted in full. The display is not redrawn in a hidden tab, and a phone may freeze the page while it is locked, but the next redraw shows the correct time.
How accurate is this online stopwatch?
The clock gives whole milliseconds and the display shows hundredths of a second, rounded down. Your own reaction time when you press the button, and a screen that redraws about every 17 milliseconds at 60 hertz, matter more than the clock. Browsers can also reduce clock precision for privacy: Firefox with resist fingerprinting on rounds to about 16.7 ms.
What do the keyboard shortcuts do?
Space starts and stops the stopwatch, L records a lap and R resets it. They do nothing while you type in a text box or list, when you hold Ctrl, Alt or Command, or for Space while a button or link has the focus. There is a switch to turn them off.
How many laps can I record, and how do I copy them?
Up to 999 laps. Use Copy laps as text for a message or note, or Copy laps as CSV for a spreadsheet. Each lap has its time and the total on the stopwatch.
Is my time saved if I reload the page?
No. The page keeps nothing in storage and sends nothing anywhere, so reloading or closing the tab clears the time and the laps. Copy the laps first if you need them.
Why is no lap marked fastest or slowest?
At least two laps are needed, and they must not all take exactly the same time. With one lap, or laps that tie, there is nothing to single out.
Does a screen reader read out the time all the time?
No. The running time is marked as a timer with live announcements off. A short polite message is made when you start, stop, take a lap or reset, such as the lap time and the total.
Sources & references
Updated Oct 15, 2026