Marathon Time Predictor
Predict your marathon or half-marathon finish time from a recent race result using Riegel's formula.
100% client-side · no upload
Marathon (42.195 km)
Half-Marathon (21.0975 km)
How to use
- Enter the distance of a recent race in kilometres (e.g., 5 for a 5 km parkrun).
- Enter your finish time in MM:SS format (e.g., 20:00) or HH:MM:SS for longer races.
- Click Predict Marathon Time to see your projected marathon and half-marathon times.
Related sport tools
- Running Pace Calculator — convert pace and speed, calculate splits
- Training Load Calculator — session RPE × duration stress score
- VO₂ Max Estimator — estimate aerobic capacity from heart rate
- Heart Rate Zones — five-zone training breakdown
Frequently Asked Questions
- Is this marathon predictor free?
- Yes, completely free with no signup and no usage limits.
- Does my data leave my device?
- No. All calculations run in JavaScript inside your browser. Nothing is sent to any server.
- Does it work on mobile?
- Yes. The tool is mobile-first and works on iPhone Safari and Android Chrome.
Last updated: By jarvisbox