Race Time Predictor - Predict Your 10K, Half Marathon or Marathon Time
Race Time Predictor
From a recent race to a finish-time estimate
Any Distance
Choose a standard distance or type your own in kilometres, for the race you ran and the race you want to predict.
Pace and Speed
See the pace per kilometre and per mile and the average speed for the predicted time.
All Distances at Once
A list shows the predicted time for every standard distance from the mile to the marathon.
Private
Nothing you enter leaves your browser.
How Race Predictions Work
In 1977 the engineer Pete Riegel noticed that a runner’s best times at different distances follow a simple pattern: the time grows slightly faster than the distance. His formula multiplies your known time by the ratio of the two distances raised to a power of about 1.06. Doubling the distance therefore takes about 2.08 times as long, not exactly twice as long, because you tire.
The formula works best between distances that are not too far apart and for runners who have trained for the longer race. A fast 5K does not guarantee a fast marathon without the mileage behind it, so treat predictions to longer distances as a best case. Race conditions such as heat, hills and wind change the real result, so for training use the pace figures as a guide rather than a promise.
Key Takeaways
- Use a recent, hard effort: The best input is a race or a time trial run at full effort in the last few weeks.
- Longer is harder to predict: Predicting a marathon from a 5K assumes endurance training that the 5K does not show.
- Related calculators: See also the Running Pace & Split Calculator, the Target Heart Rate Calculator and the VO2 Max Calculator.