The duration remains correct because it is computed from a monotonic clock. Visual updates may slow down in background tabs because browsers save resources.
Online Stopwatch
Precise stopwatch with laps and splits in your browser
Duration should be measured with a monotonic clock, not the system clock
A stopwatch measures duration, not date. This tool uses the Performance API, which provides monotonic time: it does not go backwards when the system clock is adjusted. The interface updates at the browser cadence, while the duration is computed from real elapsed time.
Time, pause and record laps
- Click start to begin counting and pause to freeze the current time.
- Use lap to record total elapsed time and the split since the previous lap.
- Use reset to clear the stopwatch and remove the lap list.
Sources and references for this tool
These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.