⏱️ Online Stopwatch with Lap Timer

What is the Online Stopwatch?

A stopwatch measures the time that passes between the moment you start it and the moment you stop it, which is called elapsed time. Unlike a clock, which tells you the time of day, a stopwatch always begins at zero and counts up. That makes it the right tool whenever you care about a duration rather than a moment: how long a lap took, how many seconds a chemical reaction ran, or how long you spoke. This is the opposite of a countdown timer, which starts at a set value and counts down to zero before sounding an alarm. If you need a fixed duration with an alert at the end, reach for a countdown timer instead; if you want to measure how long something takes as it happens, this stopwatch is the tool.

Under the hood the stopwatch reads elapsed time from the browser high-resolution performance clock rather than counting ticks. When you press Start it records a reference point, and on every update it works out the elapsed time as the difference between the current instant and that reference. Deriving the time from the live clock on each frame, instead of adding a fixed amount every interval, is what keeps the reading honest. If the browser slows the update timer down, or your device is busy for a moment, the next visible update still shows the true elapsed time because it is measured, not accumulated. It also means adjusting your system clock while the stopwatch runs will not throw the count off.

The lap feature records a checkpoint while the clock keeps running. Each lap shows two numbers: the cumulative time, which is the total elapsed time at the instant you pressed Lap, and the split in parentheses, which is how long that single segment took since the previous lap. Runners, swimmers, and cyclists use lap times to compare each repetition and the cumulative time to judge overall pace. Pausing keeps the accumulated time in place, so pressing Start again continues from where you left off rather than starting over. Only Reset returns the display to 00:00.00 and clears the lap list.

Because everything runs as plain JavaScript in your browser, the stopwatch is free, needs no sign-up, and works offline once the page has loaded. Nothing you time is uploaded or saved, so reloading the page starts you fresh. Typical uses span fitness intervals, cooking and brewing, science and lab experiments, timing typing or reading speed, keeping a talk within its slot, and timing turns in games.

When to use it

• Timing workout intervals, rounds, or rest periods, and comparing each repetition with the lap feature.
• Recording split times for running, swimming, or cycling laps without pausing the count.
• Rehearsing a speech or presentation to keep it within an allotted time.
• Timing cooking, brewing, or science experiments where the duration matters more than the clock time.
• Measuring typing or reading speed by timing how long a passage takes.
• Timing turns, rounds, or challenges in board games and party games.

How to use the Online Stopwatch

1. Press Start to begin timing up from 00:00.00.
2. Press Lap to record a checkpoint while the clock keeps running; each lap is added to the list below.
3. Press Pause to hold the current time; the elapsed count is kept.
4. Press Start again to resume counting from where you paused.
5. Press Reset to clear the time and all recorded laps back to 00:00.00.

Formula & method

Worked examples

How elapsed time maps to the MM:SS.CS display

What each stopwatch control does

Common mistakes to avoid

• Expecting the stopwatch to beep or alarm. A stopwatch counts up and has no end point, so it never sounds an alarm. If you want an alert after a set duration, use a countdown timer, which starts at a chosen value and beeps when it reaches zero.
• Confusing the cumulative time with the split. In the lap list, the first number is the total time elapsed so far and the number in parentheses is the split, how long that one segment took since the previous lap. If your laps are 30 s each, the splits stay near 30 s while the cumulative time keeps climbing (30, 60, 90 and so on).
• Expecting Reset to pause first. Reset clears everything at once, including the lap list. If you only want to hold the current reading, press Pause instead, which keeps the time so you can resume with Start.
• Assuming a background tab updates the display in real time. Browsers slow down timers in hidden or inactive tabs to save power. The elapsed time is still measured correctly from the start point, so the number is right, but the on-screen display may only catch up when you switch back to the tab.

Glossary

Elapsed time

The duration that passes between starting and stopping the stopwatch, always counted up from zero.

Countdown

The opposite of a stopwatch: a timer that starts at a set value and counts down to zero, usually ending with an alarm.

Split

How long a single segment took, measured from the previous lap to the moment you press Lap.

Cumulative (lap) time

The total elapsed time at the instant a lap is recorded, also called the running or total time.

Centiseconds

The two digits after the decimal point in MM:SS.CS, each representing one hundredth (0.01) of a second.

Tab throttling

A browser power-saving behaviour that slows down timers in background tabs, which can delay when the display updates even though the measured time stays accurate.

Frequently asked questions