Running Pace & Finish Time Predictor
Enter any run — distance and finishing time — and get your pace and speed, plus evidence-based predictions for 5K, 10K, the half marathon and the marathon using the Riegel endurance formula.
Your numbers
Hours : minutes : seconds
Result
How it works
Predictions use the Riegel formula, published by Pete Riegel in 1977 and still the most widely used endurance model: time scales with distance raised to the power 1.06. That exponent is the whole insight — doubling the distance more than doubles the time, because fatigue is not linear. A 52-minute 10K runner is not a 1:44 half marathoner; Riegel says about 1:55, and experience agrees.
The model assumes equal training and equal conditions for both distances. It predicts best between neighbouring distances (10K → half marathon) and worst at the extremes — a 5K time predicts an optimistic marathon for anyone who has not built marathon-specific endurance.
Good practice & limits
- Predict from a recent, hard, evenly-paced race — not a training run and not a race with a blow-up.
- Use the marathon prediction as a ceiling, then plan 2–5 minutes slower for a first marathon.
- Heat, hills and wind can each cost 1–3%. Adjust expectations, not just effort.