Lap Timer

How the Lap Timer Works

Click Start to begin. While running, click Lap to record the current lap time without stopping the main stopwatch. Each lap shows its individual split time and the total cumulative time.

The lap table highlights your best lap in green and your worst lap in a muted style. The stats area shows total laps, best lap, average lap time, and worst lap — updating in real time as you record new laps.

How to Use Lap Times to Improve Your Training

Lap timing transforms subjective effort into objective data. Whether you're running 400-metre repeats on a track, swimming sets in a pool, or cycling circuits on a closed road, split times tell you something perceived exertion never can: exactly where you're slowing down and by how much. Most athletes feel they're running at a consistent pace when in reality their splits vary by 5–15 seconds per lap — a gap that compounds over a race distance.

The key metric to watch isn't your best lap but the gap between your best and worst lap. A large gap (more than 10% difference between fastest and slowest) indicates pacing inconsistency, which typically means you started too fast and faded, or that you have significant room to improve your aerobic base. Narrowing that gap over training cycles is a reliable marker of fitness progress — it means your body is becoming more efficient and consistent under fatigue.

For runners and swimmers working on speed, negative splits — where each successive lap is slightly faster than the last — represent the most efficient race strategy. Starting controlled and accelerating into the final laps conserves glycogen stores, avoids early lactic acid accumulation, and produces faster overall times than an aggressive start that requires a slow finish. Use your lap timer to practice running negative splits in training before attempting them in competition.

Progressive Overload: Tracking Improvement Lap by Lap

Progressive overload is the foundational principle of endurance training: to improve, you must systematically increase the demand placed on your body over time. Lap times make this principle visible and measurable. When you record a workout session and compare it to the same session two or four weeks later, identical effort should produce faster lap times — or the same lap times should require less perceived effort. Either outcome confirms adaptation is happening. Honestly, seeing the numbers move is one of the most motivating things in training.

For interval training specifically, there are three variables you can adjust to apply progressive overload: the target lap time (go faster), the number of laps (go longer), or the rest interval between laps (recover less). Changing one variable at a time while keeping the others constant gives you a clean signal about which adaptation is occurring. Reducing rest while maintaining pace, for example, directly trains your lactate threshold — your body's ability to sustain higher intensities before fatigue becomes limiting.

A simple but effective tracking habit: after each interval session, note your fastest lap, slowest lap, and average lap time. Review this log monthly. If all three numbers are trending downward (getting faster) while your perceived effort stays constant or decreases, your training is working. If the numbers are stagnating despite consistent training, it is usually a signal to either increase volume, add a quality session, or — just as often — add more recovery to let adaptation consolidate.

For the person who pastes lap data into a spreadsheet

The CSV export was the most-requested thing. Click download, open in Excel or Google Sheets, done — your lap number, split time, cumulative time, and delta vs average are all there. The pace delta column is what makes a session actually readable: a row showing +0:03.21 tells you that lap was three seconds slower than your average, without you having to calculate it. Keyboard shortcuts work throughout: Space to start or record a lap, L for lap alone, S to stop, R to reset. Hands stay on the keyboard or the stopwatch, not the mouse.

The timer runs on performance.now() — the monotonic high-resolution clock browsers expose for animation work — so the elapsed time is accurate to fractions of a millisecond and never drifts, even on long sessions. Sessions auto-save to localStorage, so if you accidentally close the tab mid-workout you can reopen and the laps are still there. We didn't add cloud sync or account creation. If you want your lap history in three years, export the CSV.

Frequently Asked Questions