Race Time Predictor
Enter a recent race result to predict your time at every other distance. Switch to the conservative model if your weekly mileage is modest.
Roll a digit ↕
- Pace
- 5:00 /km
- Marathon prediction
- 3:59:47
Flick the tape · pull your finger down for fine control
Predicted from a 25:00 5K
The Riegel formula with its classic 1.06 exponent. Most accurate when your training already supports the longer race.
Workout paces
Interval targets based on your equivalent 5K effort.
| Rep | Target |
|---|---|
| Mile | 7:58–8:15 |
| 1000m | 4:45–5:00 |
| 800m | 3:43–3:55 |
| 400m | 1:46–1:52 |
| 200m | 0:46–0:51 |
- 1Use a recent, all-out race on a flat course; time trials and hilly races skew predictions.
- 2Predictions from a 5K to the marathon stretch the furthest; a half marathon result predicts a marathon best.
- 3Switch to the conservative model if you run fewer than about 50 km or 30 miles per week.
How to use this calculator
- 1Choose the distance of your recent race.
- 2Flick the tape, roll the digits, or type your finish time on the bib.
- 3Read the predicted times and paces, and compare the standard and conservative models.
Example marathon predictions
| Recent result | Standard | Conservative |
|---|---|---|
| 20:00 5K | 3:11:49 marathon | 3:20:11 marathon |
| 25:00 5K | 3:59:47 marathon | 4:10:14 marathon |
| 50:00 10K | 3:50:01 marathon | 3:56:44 marathon |
| 1:45:00 half marathon | 3:38:55 marathon | 3:41:58 marathon |
Frequently asked questions
How does the race time predictor work?
It uses the Riegel formula: predicted time equals your known time multiplied by the distance ratio raised to the power 1.06. The conservative model uses 1.08 when predicting a longer race.
Why is my marathon prediction faster than I expect?
Race predictors assume you have the endurance for the longer distance. Without high weekly mileage and long runs, real marathon times usually land slower than the standard prediction, which is what the conservative model accounts for.
Which race predicts a marathon best?
A recent half marathon is the most reliable predictor because it tests similar endurance. A 10K is reasonable; a 5K is the least reliable for marathon predictions.