Race time predictor
Enter a recent race result to estimate how fast you could run other distances with the same fitness using Reigel's formula
Your race
Finish time
h
min
s
Predicted times
Predictions marked less reliable reach more than four times further or shorter than your 5K, or fall outside the 3½ to 230 minutes the formula was fitted to.
When it works best
- Your result is recent, and you ran it all out on a flat course in good conditions.
- The distance you are predicting is close to the one you ran: a 10K from a 5K, or a half marathon from a 10 mile.
- You have trained for the distance you are predicting. The formula assumes you are as ready for that race as you were for the one you ran.
Where it falls short
- The further apart the two distances, the less accurate the prediction.
- From short races it usually predicts marathon and ultra times that are too fast, unless you have built the long runs and weekly mileage those races need.
- The 1.06 in the formula is an average across runners. Speed-minded runners slow more as races get longer; endurance-minded runners slow less.
- It knows nothing about the course, the weather, hills or how you pace the race.
How it works
The predictor uses Riegel's formula, from Pete Riegel's study of endurance records published in 1981:
T₂ = T₁ × (D₂ ÷ D₁)1.06
T₁ and D₁ are your result's time and distance, and D₂ is the distance you want a time for. Doubling the distance multiplies the time by about 2.085 rather than 2, because pace drops off as races get longer: a 20:00 5K predicts a 41:42 10K.
Work out splits for your goal with the pace calculator