Race Time Predictor (Riegel)
Use one race result to estimate your time at another distance.
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Race Time Predictor (Riegel) by TheCalcTools
How the Race Time Predictor (Riegel) works
Enter a recent race distance and time, and the distance you want to predict.
The Riegel formula scales time by the ratio of distances raised to a fatigue exponent, usually 1.06.
A higher exponent models a bigger slowdown over longer distances.
The formula
Worked example
Using the default values shown in the calculator:
| Recent race distance (km) | 5 |
|---|---|
| Recent finishing time (minutes) | 25 |
| Target distance (km) | 10 |
| Fatigue exponent | 1.06 |
- T₂ = 25 × (10 ÷ 5)^1.06 = 25 × 2.0846 = 52.12 minutes.
- That is 0:52:07 at a pace of 5:13 per km.
Result:
| Predicted time | 0:52:07 |
|---|---|
| Predicted pace per km | 5:13 |
| Predicted minutes | 52.12 |
Frequently asked questions
How reliable is a prediction?
It works best when the distances are fairly close and you have trained for the longer one. Predictions for a marathon from a 5K are usually optimistic.
What should the exponent be?
1.06 is the standard value. Endurance-trained runners may fit a lower figure and speed-oriented runners a higher one.
Sources and further reading
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This calculator gives general estimates for information and education. It is not medical advice and does not diagnose anything. Talk to a qualified health professional about your own situation. See our disclaimer.