Race time predictor.
Enter a recent race result and see what the same effort suggests over a mile, 5K, 10K, 10 miles, a half marathon and a marathon, with the pace for each.
These tools are free to use without an account.
Predicted finish times from 5 km in 25:00
| Race | Predicted time | Pace per km | Pace per mile |
|---|---|---|---|
| 1 mile | 7:31 | 4:40 | 7:31 |
| 5K (your result) | 25:00 | 5:00 | 8:03 |
| 10K | 52:07 | 5:13 | 8:23 |
| 10 miles | 1:26:19 | 5:22 | 8:38 |
| Half marathon * | 1:55:00 | 5:27 | 8:46 |
| Marathon * | 3:59:47 | 5:41 | 9:09 |
* More than four times shorter or longer than your result, so least reliable. A marathon predicted from a short race assumes training for the full distance.
Fitness estimates for adults 18 and over, not medical or dietary advice. Results are informational and are not reviewed by a certified personal trainer.
How the prediction works
The tool uses the Riegel formula: the new time equals your time multiplied by the new distance divided by your distance, raised to the power 1.06. The exponent is above 1 because pace slows as the distance grows. A 25:00 5K, for example, predicts about 52:07 for 10K. Enter a recent, honest race or all-out effort over a measured distance, in miles or kilometres, with the time as m:ss or h:mm:ss.
Why predictions can be optimistic
The formula assumes similar training for each distance, similar conditions and an evenly paced effort. It cannot know your weekly mileage, the hills on the course or the weather. Predicting a marathon from a 5K is the classic stretch: the formula tends to be optimistic unless your long runs match the distance. Rows more than four times shorter or longer than your result are marked as least reliable. Use the numbers as a planning range, not a promise.
Fitness estimates for adults 18 and over, not medical or dietary advice. Results are informational and are not reviewed by a certified personal trainer. Calculations stay in your browser. Typed measurements are not sent or saved.
Common questions.
What is the Riegel formula?
It is an endurance-prediction formula published by Pete Riegel: T2 = T1 × (D2 ÷ D1)^1.06, where T is time and D is distance. It estimates a time for a new distance from one result.
Can I predict a marathon from a 5K?
You can, but the result is the least reliable kind. Short races do not test the endurance a marathon asks for, so the prediction assumes training you may not have done. Predictions from a 10K or half marathon are more dependable.
How accurate is the prediction?
It is an estimate. It works best between about 5K and the marathon for a runner trained for the longer distance, and it cannot see your training, the course or the weather. Treat it as a planning range.
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