Online Stopwatch
A precise stopwatch with lap and split timing. Press Start to begin, Lap to record a segment, and Reset to clear. Everything runs in your browser and works offline.
How this stopwatch works
Unlike a clock, which reports the current time of day, a stopwatch measures a duration: the amount of time that passes between two moments. This tool does that by reading the browser's high-resolution timer, performance.now(), when you press Start and again on every animation frame. Subtracting the two values gives the elapsed time. Because that timer is monotonic, meaning it only ever moves forward at a steady rate, the measurement is immune to changes in your system clock, daylight-saving shifts, or network time synchronization that could otherwise make a naive timer jump.
The visible digits refresh using requestAnimationFrame, which lets the browser update the display in step with your screen, typically around 60 times per second. Crucially, the elapsed time is recalculated from the real start timestamp on each frame rather than by adding a fixed amount, so the total stays accurate even if the browser throttles updates while the tab is in the background. When you return to the tab, the reading immediately reflects the true elapsed time rather than a count of frames that were skipped.
Laps and splits explained
The two timing concepts people most often confuse are the lap and the split. A split time is the total elapsed time from the start to the instant you press the button, while a lap time is the duration of only the most recent segment. If you press Lap at the one-minute mark and again at the two-minute-thirty mark, the splits are 1:00 and 2:30, but the laps are 1:00 and 1:30. This stopwatch records both at once, listing the individual lap in the Split column and the running total in the Total column so you never have to subtract by hand.
Lap timing is what makes a stopwatch useful for anything repetitive. Runners use it to compare each lap of a track, swimmers to check each length of the pool, and presenters to keep each section of a talk on schedule. To make patterns obvious, the fastest lap in your list is highlighted in green and the slowest in red, so you can see at a glance where you sped up or slowed down without reading every row.
Common uses for an online stopwatch
A browser stopwatch is handy precisely because it needs no app and no hardware. Athletes and coaches use it for interval training and timed drills. Cooks lean on it for steeping tea, resting dough, or timing a boil when a kitchen timer is out of reach. Students and professionals use it for the Pomodoro technique and other focused-work intervals, and for rehearsing timed presentations or exam essays.
It is equally at home in technical and everyday settings: timing how long a process takes, measuring reaction speed, running science-fair experiments, or simply settling who finished first. Because the tool keeps a full lap history on screen, it works as a quick stand-in for a proper lap counter whenever you need to capture several segments in a row.
Frequently Asked Questions
How accurate is this online stopwatch?
The stopwatch measures time with the browser's high-resolution performance clock, which is monotonic and does not jump when your system clock changes. The display shows hundredths of a second. Actual precision depends on the browser, device, and input timing; the visible digits are not a guarantee of millisecond accuracy.
What is the difference between a lap and a split?
A split is the cumulative time from the start to the moment you press the button. A lap is the time of just the most recent segment, that is, the difference between two consecutive splits. This stopwatch shows both: the Total split column is cumulative, and the Lap time column is the individual interval.
Does the stopwatch keep running if I switch tabs?
Yes. Because timing is based on elapsed real time rather than a counter that increments each frame, the measured duration stays correct even if the browser pauses animation in a background tab. When you return to the tab, the display catches up to the true elapsed time.
Will I lose my time if the page reloads?
Reloading the page resets the stopwatch, since it runs entirely in your browser with no saved state. If you need a permanent record, note your lap times before refreshing. This local-only design also means none of your timing data is sent anywhere.
Can I use the stopwatch offline?
Yes. Once the page has loaded, the stopwatch needs no further network connection and runs completely on your device. You can disconnect and it will keep timing without interruption.
Measure a session clearly
Elapsed time, laps, and splits
Start the stopwatch when the session begins, pause it to exclude a break, and resume to continue the same elapsed total. Reset starts a fresh measurement. Take laps to mark the end of a repeated activity without stopping the running timer.
A lap is the interval since the previous lap; a split is the total time since the start. If the first split is 20 seconds and the second split is 45 seconds, the second lap took 25 seconds.
Browser timing has practical limits
The timer derives elapsed time from a monotonic performance clock rather than counting animation frames. A busy browser can draw fewer frames without turning each missed frame into lost stopwatch time.
Device sleep, browser suspension, closing the page, or a reload can disrupt a browser session. Keep the page open and the device awake when measuring something important. Do not treat displayed hundredths as a guarantee of measurement accuracy.
For three practice rounds, press Lap after each round and compare the individual lap durations. The cumulative split tells you total session time; the lap duration tells you which round was fastest.
A common mistake to avoid
This stopwatch is a session tool. Copy or record the results you need before resetting or closing the tab.