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Race Predictor Calculator

Predict your race time for any distance based on a recent result using the Riegel formula.

Reviewed October 7, 2026 Runs in your browser — inputs are never stored

Race Predictor Calculator

Uses the Riegel formula: T₂ = T₁ × (D₂/D₁)^1.06

Predicted Time

52:07

For 10 km

This tool provides general sports and fitness estimates for educational purposes only. It is not medical advice — consult a physician before starting or intensifying training, especially if you have a cardiovascular condition.

About the Race Predictor Calculator

The race predictor estimates finish times at other distances from a recent race using Peter Riegel’s formula, T₂ = T₁ × (D₂ ÷ D₁)^1.06. The exponent reflects how pace slows as distance increases. Predictions are most reliable between similar distances and assume equal training for the longer race.

How to use it

  1. 1Enter the distance of a recent race.
  2. 2Enter your finish time in minutes.
  3. 3Enter the distance you want to predict.

Worked example

a 25-minute 5K predicts about 52:07 for 10K, 1:55:00 for a half marathon and 3:59:47 for a marathon.

Common use cases

  • Choosing a goal for an upcoming race
  • Comparing performances at different distances
  • Planning training paces

Frequently asked questions

A:Typically accurate within 5% for distances from 5K to marathon for trained runners.

Reviewed for accuracy · Last updated October 7, 2026

Formulas follow published sports-science literature and official league definitions (Karvonen heart rate reserve, Cooper and Bruce protocols, MET compendium values, and standard baseball, cricket, and basketball statistics).

CW

CalcWisee Editorial Team

Calculator development and formula review

CalcWisee is an independent site founded by Ayman. Every calculator is built from a published formula or official definition, tested against hand-worked examples before it goes live, and corrected promptly when a reader reports an issue to ayman@calcwisee.com.

Expertise: Financial mathematics, Health and fitness formulas, Applied mathematics, Unit conversion standards

References & sources

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