Race Calculator
Enter a recent race result and instantly predict your finish times for other distances using the proven Riegel formula.
5K
21:35
4:19/km
10K
45:00
4:30/km
15K
1:09:10
4:37/km
Half Marathon
1:39:17
4:42/km
Marathon
3:27:01
4:54/km
This calculator uses the Riegel formula (T2 = T1 × (D2/D1)^1.06), developed by researcher Pete Riegel in 1977. It accounts for the natural slowdown that occurs as race distance increases, making it one of the most accurate race prediction methods available.
For best results, use a recent race time (within 4-6 weeks) from a distance close to your target. The formula works best when predicting between similar distances. Training specifically for your goal race will help you exceed these predictions.
Get a personalized training plan that adapts to your fitness level and race goals. Our AI coach creates weekly workouts designed to help you hit your predicted times.