Race Time Predictor
Quick answer: Enter a known distance and time to predict 5K, 10K, half, and full marathon times.
Predict your race times across distances using the Riegel formula: T2 = T1 × (D2/D1)^1.06. Enter any race time you've run and instantly see predicted times for all standard distances.
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Last reviewed: April 2026Report an error
Predicted Marathon Time
3:59:47
Based on your 3.11 mile time, the Riegel formula predicts these race times.
5K
25:00
10K
52:07
Half marathon
1:55:00
Marathon
3:59:47
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How to Use This Race Predictor Calculator
- 1Click a quick preset (5K, 10K, half, marathon) or enter a custom distance in miles.
- 2Enter the time you ran that distance (hours, minutes, seconds).
- 3Read predicted times for all four standard race distances.
Frequently Asked Questions
- It assumes proper training for the target distance. A well-trained 5K runner who has not done long runs will run slower than the predicted marathon time. Use it as a goal, not a guarantee.
- It accounts for the slowdown that happens at longer distances. Running twice as far takes more than twice as long because endurance limits speed.
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