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Race time predictor
Predict your marathon, half marathon, 10K or 5K time from a recent race result. The race time predictor uses Riegel's formula and lets you change the fatigue exponent. Free online, with predicted times and paces for every distance.
How to predict your race time
- 1Pick the race you ran and enter your time
- 2Choose the distance to predict
- 3Adjust the fatigue exponent if you like
- 4Read the predicted time and pace
- A predicted time, plus a table for all distances.
What you get
- One result, one table.The distance you chose is shown big, and every other race is listed with time and pace.
- Your own exponent.Change Riegel's 1.06 to suit how much long-run training you do.
- Stays in your browser.Times are calculated on your device and sent nowhere.
What you can do
- Start from 1 km, 1 mile, 5K, 10K, a half marathon, a marathon or a custom distance in km or miles.
- Predict a time for 1 km, a mile, 5K, 10K, a half marathon or a marathon.
- Set the fatigue exponent between 1.00 and 1.30. The default is 1.06. The tool suggests 1.08 to 1.1 if you run few long runs.
- Write times as 25:00 or 1:45:30.
- See the pace per kilometre and per mile next to every predicted time.
Good to know
- Riegel's formula assumes you have trained for the distance you predict. A marathon prediction from a 5K can be too fast without long runs.
- Predictions are for an even pace on a similar course and in similar conditions.
- A time that is not written as minutes:seconds or h:mm:ss gives an error.
Questions
How accurate is a race time prediction?
It is a good guide when the distances are close and you have trained for the longer one. For a big jump, expect to be slower.
What is the fatigue exponent?
It is how fast your pace slows as the distance grows. Riegel used 1.06. A higher number predicts a slower long race.
Can I predict a marathon from a 10K?
Yes. Pick 10K as the race you ran, enter your time and choose marathon under Predict.
Is my time sent anywhere?
No. It is calculated in your browser.