A simple stopwatch that counts up from zero and stays accurate even if you switch tabs — it reads the real clock, not just a counter, so time never freezes or drifts in the background. Press start to begin timing, pause whenever you need, and tap lap to record split times. Free, and runs entirely in your browser — nothing to install, nothing to sign up for.
About this stopwatch
An online stopwatch is a timer that counts up from zero so you can measure how long something takes. Press Start to begin, Stop to pause without losing your time, and Reset to clear it back to zero. The Lap button records the time for each segment along with the running total — useful for runners timing intervals, cooks timing steps, or anyone timing repeated tasks. It reads the time from your device's clock and only counts while running, so it stays accurate over long sessions. Everything happens in your browser; nothing is uploaded or stored.
Frequently asked questions
- How accurate is this online stopwatch?
- It uses your device's high-resolution clock and only counts the time the stopwatch is actually running, so it stays accurate even when you pause and resume and does not drift over long sessions.
- What does the lap button do?
- Each tap records a lap, showing how long that single lap took and the total time so far. It is handy for timing repeated activities like running intervals or workout sets.
- Does the stopwatch keep running if I switch tabs?
- Yes. The elapsed time is measured from the real clock, so when you come back to the tab the display catches up to the correct time.
How Digital Timekeeping Operates
Digital stopwatches function by calculating the difference between two timestamps generated by the system clock. When the start button is pressed, the application records the current Unix epoch time in milliseconds. As the display updates, the software subtracts this initial starting timestamp from the current system time to determine the total elapsed duration.
This method relies on the high-resolution performance.now() API in modern web browsers, which provides timestamps with microsecond precision. Unlike standard Date objects that can be affected by system time synchronization or manual clock adjustments, this performance timer is monotonic, meaning it only moves forward at a constant rate. This ensures that the duration remains consistent even if the operating system updates its internal clock during a timing session.
The most frequent error users encounter is assuming that a web-based timer can achieve absolute millisecond synchronization across different devices. Browser-based timers are subject to the event loop latency of the JavaScript engine, which can introduce minor jitter if the browser is under heavy processing load. While the underlying calculation is mathematically exact, the visual frame updates may occasionally lag by a few milliseconds depending on the device hardware capabilities.