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Health & Fitness

Race Time Prediction Calculator

Predict race times at other distances from a recent result using Riegel’s endurance formula.

Your inputs

Riegel’s 1.06 is standard; less endurance-trained runners may slow more.

Results

Predicted time

3:50:01

Predicted pace per km
5:27
Predicted time in seconds
13,801

≈Estimate based on the stated model and assumptions

Notes for this result

  • Predictions assume equivalent training for the target distance. They are less reliable when extrapolating more than about 4× the distance or for very short races.

Inputs are never added to links for financial, salary or health calculators.

What this calculator does

Riegel’s formula models how pace slows as distance increases, so a recent race can predict an equivalent time at another distance.

Formula and method

T₂ = T₁ × (D₂ ÷ D₁)^1.06

Worked example

Calculated by this tool with its default inputs:

Inputs

  • Recent race distance: 10K
  • Your time (h:mm:ss or mm:ss): 50:00
  • Predict for: Marathon
  • Fatigue exponent: 1.06

Results

  • Predicted time: 3:50:01
  • Predicted pace per km: 5:27
  • Predicted time in seconds: 13,801

How to read the results

Predictions assume equivalent training for the longer distance, which matters especially for marathons.

Assumptions and limitations

  • Least reliable when extrapolating far (e.g. from a mile to a marathon).

Health results are general estimates for adults and do not replace medical advice, diagnosis or treatment. Speak to a qualified health professional about your personal situation, especially during pregnancy or if you have a medical condition.

Questions

Can I change the exponent?

Yes — runners with less endurance training often slow more, which a slightly higher exponent reflects.

Sources

  • Riegel PS. Athletic records and human endurance. American Scientist. 1981;69(3):285–290.

Methodology and verification

Result type
Estimate based on the stated model and assumptions
Formula version
1.0
Automated verification
3 reference and validation test cases, checked against independently computed values. The site cannot be built if any of them fail.
Editorial review
Awaiting human editorial review. The explanation was drafted with AI assistance; the formula and examples are verified by the automated tests above.

Privacy

Everything you enter is calculated in this browser and is not sent to Numerith or anyone else. Because this calculator can involve personal financial or health details, your inputs are never added to share links or saved to history. Privacy policy