Predict your potential finish times across multiple distances using Riegel's famous formula.
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Predicted Times
Enter your recent race time to see predictions
About this calculator
Riegel's Formula
Peter Riegel's formula (t2 = t1 * (d2 / d1)^1.06) is the gold standard for race prediction. It assumes that a runner slows down at a predictable rate as distance increases due to fatigue.
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Pro Tips
Predictions are most accurate when the input distance is close to the target distance (e.g., predicting a 10k from a 5k is better than from a 100m sprint).
The formula assumes you have done the appropriate endurance training for the longer distance.
Weather, terrain, and race-day adrenaline can all significantly affect actual results.
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Fun Facts
"The exponent 1.06 represents the average rate of fatigue for elite runners. Some recreational runners may have a higher fatigue factor (around 1.15)."
"The 'Marathon Wall' typically hits around mile 20 (32km) where glycogen stores deplete, causing a sharper slowdown than the formula predicts."
"Negative splitting (running the second half faster than the first) is a common strategy for achieving predicted times."
