Race Time Predictor

Predict a race time at another distance from a known result with Riegel's formula.

Predict a race time

Known distance

Known time

Target distance (km) Fatigue exponent

Predicted time: —

Equivalent pace: —

Average speed: —

Predictions use Riegel's formula and are an estimate for general information and not medical advice.

Enter a recent race distance and the time you ran for it.
Set the distance you want to predict and adjust the fatigue exponent if needed.
Read the predicted time, the equivalent pace and the table for common distances.

Common questions about the free online race time predictor.

It applies Riegel's formula, multiplying your known time by the ratio of the two distances raised to a fatigue exponent.

The formula is T2 equals T1 times the distance ratio to the power of 1.06, which models how pace slows over longer races.

The exponent controls how much you slow down. The classic value is 1.06, while 1.07 to 1.10 suits runners who fade more.

Use a recent race or hard time trial at a similar effort. Training runs and very short sprints give poor predictions.

They are usually close for distances within about a factor of two, but heat, hills and course type still change the real result.

Yes. Set a shorter target distance and the formula returns the faster time you should be capable of over that distance.

No. Race predictions are an estimate for general information and not medical advice, so train within your own limits.

Yes. The race time predictor is completely free, works offline in your browser and needs no account or sign-up.

Last updated: October 10, 2026