Cardio tool
Race time predictor
Predicts your finish time at a new distance from a recent race using Riegel's formula: T2 = T1 × (D2 ÷ D1)^1.06. Accuracy is best when the distances are reasonably close and you're trained for the longer one.
- Predicted pace
- 5:13 /km
Riegel's formula — most accurate when the distances are close and you're trained for the target.
The basics
What is Race Time Predictor?
This predicts your race time at one distance from a recent result at another, using Peter Riegel's endurance formula: T2 = T1 × (D2/D1)^1.06. The 1.06 exponent reflects that we slow slightly as distance grows. It's most accurate when the two distances aren't too far apart and you've trained appropriately — a 5K time only predicts a marathon if you've done the marathon endurance work.
How to use it
- 1Enter a recent result. Input the distance and time of a recent race or hard effort.
- 2Enter the target distance. Input the distance you want to predict.
- 3Read your prediction. Your predicted finish time and pace appear instantly.
FAQ
Race Time Predictor — questions
How accurate is the race time predictor?
Riegel's formula is reliable when the known and target distances are reasonably close and you've trained for the longer one. Predicting a marathon from a 5K overstates your fitness unless you've built the endurance base.
What formula does it use?
The Riegel endurance formula: predicted time = known time × (target distance ÷ known distance) raised to the power 1.06.
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