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Race Time Predictor

Predict your finish time for any race distance using Riegel's formula.

Introduction

Race Time Predictor — Predict your finish time for any race distance using Riegel's formula. Enter Known distance (km), Known time (minutes), Target distance (km) to get an instant, accurate result.

Formula

Riegel's endurance race-time formula (Pete Riegel, 1977): T2 = T1 × (D2/D1)^1.06, where T1 is your known finish time, D1 is that known distance, and D2 is the target distance.

Step-by-step

  1. Enter the Known distance (km).
  2. Enter the Known time (minutes).
  3. Enter the Target distance (km).
  4. Click Calculate to see your result instantly.

Real-world example

Example: With Known distance (km) = 5 km, Known time (minutes) = 25 min, Target distance (km) = 10 km, the Race Time Predictor gives Predicted Time Minutes: 52.1233, Pace Per Unit: 5.2123.

Frequently Asked Questions

Why is the exponent 1.06 and not 1.0?
A pure ratio (exponent 1.0) would assume you can hold the exact same pace at any distance. Riegel's research found endurance performance degrades slightly as distance increases, so 1.06 builds in a realistic slowdown for longer races.
How accurate is this for very different distances?
It's most reliable when predicting a distance reasonably close to your known race (e.g. a 10K time predicting a half marathon). Predictions across very different distances (a 5K predicting a marathon) are less reliable since endurance and fueling factors change.
Does this account for terrain or weather?
No, the formula is a pure time/distance relationship and assumes similar conditions (course, weather, effort) for both races.
What inputs does the Race Time Predictor need?
You'll need to provide: Known distance (km), Known time (minutes), Target distance (km). All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.
How accurate is the Race Time Predictor?
The Race Time Predictor applies the formula exactly as calculated — Riegel's endurance race-time formula (Pete Riegel, 1977): T2 = T1 × (D2/D1)^1.06, where T1 is your known finish time, D1 is that known distance, and D2 is the target distance. — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.
Is the Race Time Predictor free to use?
Yes, the Race Time Predictor is completely free, requires no signup, and runs instantly in your browser.

About the Race Time Predictor

The Race Time Predictor uses a real, verifiable formula — Riegel's endurance race-time formula (Pete Riegel, 1977): T2 = T1 × (D2/D1)^1.06, where T1 is your known finish time, D1 is that known distance, and D2 is the target distance. — so results are accurate every time, not an approximation.