Race Time Predictor Calculator

Predict a race time using Riegel's Formula from a recent result.

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How to Use the Race Time Predictor Calculator

  1. Enter the distance of a recent race in km.
  2. Enter your finish time for that race (h:m:s).
  3. Enter the target race distance in km.
  4. Click Calculate to see your predicted finish time and pace.

Formula

T₂ = T₁ × (D₂ ÷ D₁)^1.06 (Riegel's Formula)

Worked Example

A 10K finished in 50:00 predicts a half marathon (21.1km) finish of about 1:51:15.

About This Calculator

Riegel's Formula is a widely used endurance prediction model, most accurate when predicting races of similar or slightly longer distance to your recent result.

Frequently Asked Questions

How does this predict race times?

It uses formulas like Riegel's, estimating performance at one distance from a known time at another.

Are these predictions always accurate?

No — actual performance depends on training, pacing, and race-day conditions the formula can't fully capture.

Why does pace slow at longer distances?

Longer races require more endurance and pacing discipline, which formulas account for mathematically.

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