Race Time Predictor
Predict your finish time for a new race distance from a recent result using the Riegel endurance formula.
- Predicted time
- 52 min
- Predicted pace
- 5:13 min/km
Formula: T2 = T1 × (D2 ÷ D1)^1.06 (Riegel)
About Race Time Predictor
Race Time Predictor is a free online calculator that gives you an instant, accurate result as you type. Predict your finish time for a new race distance from a recent result using the Riegel endurance formula.
The calculation uses the standard formula T2 = T1 × (D2 ÷ D1)^1.06 (Riegel) and updates live with every change to the inputs. Everything runs client-side in your browser — fast, private, and free to use as often as you like.
Peter Riegel's 1981 formula T2 = T1 × (D2/D1)^1.06 assumes similar training for both distances and works best between 1.5x and 4x the known race distance.
Frequently Asked Questions
Is Race Time Predictor free to use?
Yes. Race Time Predictor is completely free, with no sign-up, no downloads, and no usage limits. You can use it as many times as you like on any device with a web browser.
How accurate is this calculator?
The calculator applies the standard formula (T2 = T1 × (D2 ÷ D1)^1.06 (Riegel)) with full floating-point precision and rounds only the displayed result. For most practical purposes the results are exact.
Why is my predicted marathon time optimistic?
Riegel's exponent of 1.06 assumes distance-appropriate training; without high weekly mileage, real marathon times are often slower than the prediction.
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