About Race Time Predictor
You just ran a blistering 5K. Naturally, you wonder: "Could I qualify for Boston?" The Race Time Predictor uses a mathematical model to project your performance across different distances based on a recent result.
The Riegel Formula
Developed by Peter Riegel in 1977, this formula is the industry standard used by Runner's World and major coaching platforms.
Time2 = Time1 * (Dist2 / Dist1)^1.06
The exponent 1.06 accounts for the natural "fatigue factor". It implies that as distance doubles, you slow down by about 6% relative to your speed.
The Critical Caveat
Prediction ≠ Guarantee. The math assumes you are equally well-trained for both distances.
A 20-minute 5K predicts a 3:10 Marathon. However, if you haven't done the 20-mile long runs required for marathon training, your legs will fail at mile 18 regardless of what your VO2 max says. Treat these predictions as "Potential" rather than promise.
How to Use
Enter a recent Race Distance and Time. Select the Target Distance you want to predict.