Race time predictor
Same formula as the Overload app
This race time predictor turns one recent result into an expected finish time for 5K, 10K, half marathon and marathon, using the Riegel formula runners and coaches have relied on for decades. Enter any distance and time you've actually run, and get predictions across every standard race distance with the pace each one implies, handy for setting a realistic goal time before your next race.
Predicted 10K time
50:00
Predicted times
| Race | Predicted time | Pace |
|---|---|---|
| 5K | 23:59 | 4:48/km |
| 10K | 50:00 | 5:00/km |
| Half marathon | 1:50:19 | 5:14/km |
| Marathon | 3:50:01 – 4:10:46 | 5:42/km |
How it works
Peter Riegel's 1981 formula predicts a new time from a known one by scaling with the distance ratio raised to the power 1.06: t2 = t1 × (d2/d1)^1.06. The exponent captures the fact that endurance, not raw speed, decides how much you slow down over a longer distance.
The marathon row uses a wider range instead of a single number, because the standard 1.06 exponent tends to be optimistic for four-plus hours of running. The low, mid and high figures apply exponents of 1.06, 1.09 and 1.12, giving a realistic band rather than a false-precision single time.
Predictions are most accurate when the input race is close in distance and demand to the target, and less reliable across very different terrains, so treat a marathon predicted from a 5K with more caution than one predicted from a half marathon.
Frequently asked questions
How accurate is a race time predictor?
Riegel's formula is reasonably accurate between races of similar demand, typically within a couple of minutes for a 10K to half marathon jump on a well-trained runner. It gets less reliable the further apart the two distances are, which is why the marathon prediction here is a range rather than one number.
Can I predict a marathon time from a 5K?
You can, but treat it as an optimistic upper bound rather than a plan. Marathon performance depends heavily on long-run endurance and fuelling that a 5K doesn't test at all, so the low end of the predicted range is usually closer to reality than the high end.
Why is my predicted 10K faster than my actual 10K?
If the prediction is based on a shorter, faster race like a 5K, the formula assumes your endurance holds up proportionally, which isn't always true. Use a result from a distance close to the one you want to predict for the most reliable number.
Related tools
- Pace calculatorSolve for running pace, time or distance from the other two, free, with instant km/h and mph conversions and a full race-distance time table.
- Pace converterConvert running speed between km/h, mph, min/km and min/mi instantly, free, with a reference table spanning 6 to 22 km/h for quick lookup.
- VDOT calculatorCalculate your Daniels VDOT, VMA and VO2max from a race result, free, with training pace zones the same way the Overload app computes them.
- Heart rate zones calculatorWork out your five running heart rate zones from age or a known HRmax, free, with the Karvonen method for a more personal result.
Overload predicts race times from your best efforts
Overload applies the same Riegel exponents to your logged runs automatically, predicting your next race time as your training progresses. Free on iOS and Android.