Race time predictor
Use a time achieved over one distance to estimate your potential performance over other standard race distances.
Previous race distance
Your time over this distance
Based on 10K in 45min 00s
This estimate is based on the Riegel formula. It provides a useful indication but does not replace training specific to your target distance.
How does race-time prediction work?
This calculator uses the Riegel formula, developed by researcher Pete Riegel and widely used by coaches to estimate performance over different distances from a known reference time. It accounts for the natural slowing of pace as distance increases — the formula's 1.06 exponent models this progressive loss of endurance.
Enter a recent race performance — usually the most reliable reference — over a known distance such as 5K, 10K, a half marathon or a marathon, then view an estimate of your potential time over other standard distances.
When is this estimate reliable?
- The prediction is more accurate between similar distances, such as 10K and a half marathon, than between very different distances, such as 5K and a marathon.
- It assumes that you have completed sufficient, distance-specific training — a 10K time will not accurately predict a marathon if you have never run more than 15 km in training.
- Prefer a race result to a training time, which is generally less representative of your maximum ability.
Using this prediction in your training plan
Once you have an estimated target time, you can use it to define your race pace with our pace calculator, or refine your training sessions with our maximal aerobic speed calculator.