Race Time Predictor
Predict your 5K, 10K, half marathon and marathon times from a recent race result using Riegel's formula.
For general information only — not medical advice. Results are estimates; talk to a doctor or qualified health professional about your own health.
How to use
- 1Enter a recent race distance and your finish time.
- 2See predicted times for other distances.
How it's calculated
T₂ = T₁ × (D₂ ÷ D₁)^1.06 (Peter Riegel, 1977).
Frequently asked questions
How accurate are the predictions?
Good for similar distances. Marathon predictions from short races are often optimistic unless you've done marathon-specific training.
Which race should I use?
A recent, all-out effort at the distance closest to your goal race.
Why the 1.06 exponent?
Riegel found that pace slows by a fairly consistent amount as distance increases; 1.06 fits a wide range of runners.