Predict your race time at a new distance from a known result.
Calculated instantly in your browser.
How do you predict a race time at a new distance?
Riegel's formula: predicted time = known time × (target distance ÷ known distance)^1.06. The exponent 1.06 reflects that pace slows as distance grows, and predictions assume similar conditions and proper training. For example, a 25:00 5K predicts about a 52:08 10K.
Understanding your result
The exponent 1.06 reflects that pace slows as distance grows. Predictions assume similar conditions and that you are properly trained for the longer distance; they are less accurate for very large jumps.
Formula and method
Riegel’s formula: predicted time = known time × (target distance ÷ known distance)^1.06.
Assumptions and limitations
Predictions are estimates from a single past result using Riegel's formula, not a training plan or guarantee. They assume similar conditions and that you are properly trained for the new distance, and they grow less reliable for very large jumps in distance. Course, weather, terrain and fitness on the day all affect real times.
Worked example
A 25:00 5K predicts about a 52:08 10K.
How to use this tool
- Enter a distance you have a time for.
- Enter that time and the target distance.
- Read the predicted time and pace.
Common mistakes to avoid
- Predicting a marathon from a single short race without the training to match.
- Entering the two distances in different units.
About the Race Time Predictor
The Race Time Predictor estimates your finish time at a new distance from a recent race result, using Pete Riegel’s endurance formula, and shows the predicted pace.
Who should use this tool
Runners planning races and setting goal times.
Benefits
- Predicts time at any target distance.
- Works in kilometres or miles.
- Shows known and predicted pace.
- Based on the proven Riegel formula.
Practical use cases
- Predicting a 10K from a recent 5K.
- Setting a half-marathon goal.
- Estimating a marathon time.
Frequently asked questions
How accurate is the prediction?
It is a solid estimate for similar distances and conditions, but real results depend on training, terrain and weather.
What formula does it use?
Pete Riegel’s formula, time₂ = time₁ × (distance₂ ÷ distance₁) raised to the power 1.06.
Can it predict a marathon from a 5K?
It can produce a number, but a jump that large stretches the formula's assumptions, since marathon performance depends heavily on endurance training and fuelling that a 5K does not test. Treat such a prediction as a rough ceiling and lean on race results at closer distances.