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Pace from distance & time.
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Running
Marathon Time Predictor
Predict your race time from a recent result — 5K, 10K, half or full marathon.
Predicted time
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For the target race.
| Predicted pace | — |
|---|---|
| Recent race | — |
| Target | — |
| Formula | — |
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Enter your figures above to see the step-by-step working.
A prediction — train accordinglyEverything computed client-side — nothing leaves this page
How the Marathon Time Predictor Works
A time at one race distance predicts your time at another remarkably well, using Peter Riegel’s formula: predicted time equals your known time multiplied by the ratio of distances raised to the power 1.06. The exponent above 1 reflects that we slow down slightly as distance grows. Feed in a recent 5K, 10K or half marathon and it estimates your 5K through marathon times.
It assumes similar conditions and, crucially, that you’ve trained appropriately for the longer distance — endurance for a marathon can’t be faked from 5K speed alone. Treat it as a well-grounded target, not a guarantee.
predicted = time × (target distance ÷ known distance)1.06
Frequently Asked Questions
How accurate is a race time predictor?
Riegel’s formula is quite good for well-trained runners racing in similar conditions. It’s less accurate if you’re undertrained for the longer distance.
Can a 5K time predict my marathon?
It gives an estimate, but the marathon demands endurance a 5K doesn’t test. Use a recent longer race for a better marathon prediction.
What is the Riegel exponent?
1.06. It captures the small, steady slowdown as race distance increases, and is the standard used across running calculators.
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