Track Day Lap Timer

Free GPS lap logger for circuit days. Set your start/finish line on the map, press Start Session, and get automatic lap times, speed heatmap, and a lap comparison chart — all in your browser, all local.

GPS: waiting

Start/Finish: not set

Session: idle

Screen: normal

Current Lap

00:00.000

— km/h

This tool uses your browser's Geolocation API. You'll be asked to allow location access when you start a session. Data never leaves your device.

#	Lap Time	Δ Best	Avg Speed	Max Speed
No laps recorded yet

How it works

1. Set the start/finish lineTap "Set Start/Finish Line", then click two points on the map straddling the finish line. A red line will appear on the map.

2. Drive to the circuitOpen this page on your phone or tablet, leave it open (WakeLock keeps the screen on), and press Start Session at the pits.

3. Automatic lap detectionThe app samples GPS every ~1 second. Each time your position crosses the line segment, a lap is recorded and the timer resets automatically.

4. Review & exportLap times appear in the table. The speed heatmap overlays on the map. Export all data as CSV for analysis in Excel or Google Sheets.

Accuracy note: Browser GPS uses device hardware. On modern phones this is typically 3–10 m accuracy. Lap detection uses line-crossing geometry (cross-product sign change), so accuracy depends on GPS update rate near the line. For best results, place the start/finish line across a straight, and ensure the phone has a clear sky view.

Frequently asked questions

Do I need an internet connection on track?: Once the page has loaded, you only need internet for the map tiles to display. GPS tracking, lap detection, and all calculations work fully offline — your lap times are never sent to a server. The map is for reference; if you lose signal the tracker keeps running.
Will my phone screen turn off while I'm driving?: The tool requests the Screen Wake Lock API when you start a session, which prevents the screen from sleeping. Wake Lock is supported on Chrome/Edge/Samsung Internet on Android, and Safari 16.4+ on iOS. If your browser doesn't support it, you'll see a warning — you can manually set your screen timeout to "Never" in device settings as a fallback.
How accurate is browser GPS for lap timing?: Accuracy varies by device. Modern flagship phones achieve 3–5 m accuracy with GPS + GLONASS + Beidou under open sky. Budget phones or indoor/parking garage use can degrade to 20–50 m. For serious timing, a dedicated transponder system (AMB/MyLaps) is more accurate — this tool is ideal for casual track days, data logging, and learning circuit layouts. Always set your start/finish line across a straight section for the most reliable crossing detection.
What does the speed heatmap show?: Each GPS point is connected to the previous by a coloured line segment on the map canvas. The colour maps to speed: blue for slow (<50 km/h), yellow for medium (50–120 km/h), and red for fast (>120 km/h). This lets you visually identify braking zones, cornering speeds, and acceleration points on any circuit.
Can I set the start/finish line before arriving at the circuit?: Yes. Pan and zoom the map to your circuit, click "Set Start/Finish Line", and place two points straddling the actual finish line position. The coordinates are saved in memory for the session. You can also set it on arrival by parking at the finish line and dropping points near your current GPS position.