Race Time Predictor Calculator

Race Time Predictor

This Race Predictor Calculator estimates your finish time at a new distance based on a recent race result. It uses the Riegel formula, the same method published in Runner's World, to project performance across 5K, 10K, half marathon, marathon, or custom distances.

The Riegel Formula

T₂ = T₁ × (D₂ / D₁)^1.06, where T₁ is your recent finish time at distance D₁ and T₂ is the predicted time at distance D₂. The exponent accounts for the fact that longer races are run at a slightly slower relative pace.

Planning Your Next Race

Enter a recent race distance and finish time, then choose your target distance. The calculator shows your predicted finish time plus equivalent pace per kilometer and per mile. For fixed-distance pace planning, try our Running Pace Calculator.

Frequently Asked Questions

How accurate is the Riegel race predictor?

Riegel's formula is widely used and reasonably accurate for trained runners at distances from 5K to marathon. It assumes you are properly trained for the target distance.

Can I predict a marathon time from a 10K?

Yes. Enter your 10K time as the recent race and select marathon as the target distance. The prediction assumes marathon-specific training, not just speed from a shorter race.

Why is the exponent 1.06?

Peter Riegel found that race times scale slightly faster than linearly with distance. The 1.06 exponent reflects fatigue over longer efforts and matches real-world running data well.

Does this work for other sports?

The formula was developed for running. It can give rough estimates for cycling or swimming only when pace-fatigue patterns are similar; sport-specific predictors are more reliable.

Report

Race Predictor Calculator