Race Time Calculator
Predict your time over a new race distance from a recent race result, using the Riegel formula.
Quick answer: enter your details below and click Calculate — your result appears instantly, right here in your browser. Nothing you enter is uploaded or stored.
R
Calculators
Enter your details below.
How to use
- Enter your known race time in minutes and its distance in kilometres.
- Enter the target race distance in kilometres.
- Read your predicted time in minutes and hours:minutes.
About this tool
The Riegel formula predicts a new race time by scaling a known time with the ratio of the two distances raised to the power 1.06, which reflects that pace fades slightly as distance grows. Enter a recent race you actually ran, plus the distance you want to predict. It is a performance estimate, not a guarantee — training, course, and weather all shift real results.
Frequently asked questions
How accurate is the Riegel prediction?
It is usually close for nearby distances, but predictions far from your known race — say from 5 km to a marathon — carry much more uncertainty.
Should I use my best or a recent time?
Use a recent race run in similar conditions; an old personal best on a fast course will flatter the prediction.