Race Time Predictor
Enter a recent race result and target distance to estimate your finish time using the proven Riegel formula.
How to use the race time predictor
- Enter the distance and finish time of a recent race.
- Choose the target distance you want to predict.
- Click Predict to estimate your finish time.
Why pace slows over longer distances
The Riegel exponent of 1.06 captures the physiological reality that you cannot hold 5K pace for a marathon. Endurance, fueling, and fatigue resistance all matter more as distance increases, which is why longer predictions assume adequate training.
Frequently asked questions
How accurate is a race time predictor?
Predictions are most accurate when the goal distance is close to your recent race and you have the endurance base to match. Predicting a marathon from a 5K tends to be optimistic without long-run training.
What formula does this predictor use?
It uses Pete Riegel's formula: T2 = T1 × (D2 ÷ D1)^1.06, which models how pace slows as distance grows.
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