Race Time Predictor

Estimate an equivalent finish time at another running distance from a recent known performance. The model is useful for planning, but it cannot account for terrain, weather, fueling, training specificity or individual endurance.

Maintained by Live Fitness Check. Last updated: August 13, 2026. How we test our calculators .

About This Calculator

The Race Time Predictor extrapolates a known running performance to another distance using the commonly used Riegel distance-time model. It can be useful for planning approximate targets, especially when the known and target races are reasonably close in distance.

Methodology

Known and target distances are standardized to kilometers. Predicted time follows T2 = T1 × (D2 / D1)^1.06. The predicted time is then divided by target distance to calculate pace per kilometer and converted to pace per international mile.

Sources

Vickers AJ, Vertosick EA — An empirical study of race times in recreational endurance runners: https://pubmed.ncbi.nlm.nih.gov/27570626/
NIST — mile and kilometer conversion factors: https://www.nist.gov/pml/special-publication-811

Disclaimer

A mathematical race extrapolation cannot account for training, terrain, weather, fueling, injury, pacing or individual endurance. Research in recreational runners found that the Riegel approach can underestimate marathon time, so treat longer-distance predictions cautiously.

Frequently Asked Questions

What formula does this predictor use?

It uses the Riegel distance-time relationship T2 = T1 × (D2 / D1)^1.06.

When is the estimate most useful?

It is generally more useful when the known performance is recent and the target distance is not dramatically different.

Why can marathon predictions be too fast?

Longer races introduce endurance, fueling and pacing demands that a simple distance exponent cannot fully model.

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