Why Online Stopwatches Lose Time in Background Tabs (and How to Avoid It)

After 10 minutes in a hidden tab, a tick-counting stopwatch was 600 seconds behind; a clock-based one was exact. Here is why, and how to keep laps accurate.

Why Some Online Timers Lose Time

The simplest way to build a stopwatch in a web page is to run a timer every few milliseconds and add that amount to a total. It works while you watch it. But browsers deliberately slow timers in tabs you are not looking at to save battery and processing power: Chrome, since version 88, can limit chained timers in a page that has been hidden for a while to about one run per minute. A stopwatch that counts its own ticks then falls behind by almost all the time you were away.

We simulated it: 5 minutes with the tab visible, then 10 minutes hidden with timers firing once a minute. A tick-counting stopwatch showed 300.3 seconds after 15 real minutes, 600 seconds behind. A stopwatch that computes elapsed time from the clock showed the full 15 minutes.

How an Accurate Web Stopwatch Works

Our Stopwatch never counts ticks. It stores the moment it was started and the time built up before any pause, and every time it draws, it computes the elapsed time from the device clock. Timers only decide how often the numbers on screen refresh, not what they say. In our test with a controlled clock and timers firing once a minute for ten minutes, it read exactly 10:18.50 against an expected 10:18.50. Because that state is saved, it also survives a reload: after reloading a running stopwatch, it was still running with the right time.

Laps Without Rounding Drift

Store each lap as the total time at the moment you pressed it, and work out lap times as differences between totals. That way the lap times always add up exactly to the total, and rounding to hundredths for display never accumulates. Our CSV export includes both the formatted times and the exact milliseconds.

What Still Limits Accuracy

A browser stopwatch is as accurate as the device clock and the moment the browser handles your click or key, which can add a few milliseconds. It is fine for workouts, classroom activities, presentations and cooking; for officially timed races, use dedicated timing equipment. If your device adjusts its clock while the stopwatch runs, for example syncing over the network, the elapsed time can jump by the size of the adjustment.

Frequently Asked Questions

Published Oct 14, 2026 by Derek Giordano