Race Time Predictor
1Your recent race
Predicted marathon time
–
Predicted times, paces and treadmill speeds
How you compare
Current world records (mile, 5,000 m and 10,000 m on the track; half marathon and marathon on the road), checked November 2026; marks set in 2026 may still await World Athletics ratification. Boston standards: B.A.A., 2027 race.
Free tool · Updated November 1, 2026
What can you run at your next race?
Enter one recent race and get your predicted times from the mile to the marathon, with the pace per mile and per km and the treadmill speed to train at each pace.
Short answer
A race time predictor scales one recent result to other distances. With the Riegel formula, T2 = T1 x (D2 / D1)^1.06: a 50:00 10K predicts about 3:50:01 for the marathon. Predictions hold best between nearby distances and when your training matches the longer race.
Key takeaways
- One recent, all-out race is the best input; training runs predict poorly.
- Riegel is simple and well tested; Cameron is often a little slower for the marathon.
- Predicting a marathon from a 5K is optimistic unless you have done the long runs.
- The treadmill speed for each pace lets you rehearse race pace indoors.
If you know what you can run for one distance, you can estimate what you can run for another. Race time predictors do this with a fatigue curve: the longer the race, the slower the pace you can hold.
Enter a recent race or time trial and the calculator predicts your mile, 5K, 10K, half marathon and marathon, with the pace per mile and per km and the treadmill speed for each pace, so you can practice it indoors.
How the Prediction Works
Peter Riegel, an engineer and runner, published the formula in 1977 and refined it in a 1981 article in American Scientist: T2 = T1 x (D2 / D1)^1.06. The exponent describes how much you slow down as the distance grows; 1.06 fits trained runners from about 3.5 minutes to 4 hours of racing.
The Cameron model, proposed by statistician Dave Cameron, fits a different curve to top results across distances and often gives a slightly slower marathon. Neither formula knows your training: if your long runs are short, add a few minutes to the half and marathon predictions, or raise the Riegel exponent to 1.08.
| Distance | Riegel (1.06)Riegel | Cameron | Riegel pacePace |
|---|---|---|---|
| 1 mile | 7:13 | 6:58 | 7:13 /mi |
| 5K | 23:59 | 24:00 | 7:43 /mi |
| 10K | 50:00 | 50:00 | 8:03 /mi |
| Half marathon | 1:50:19 | 1:50:14 | 8:25 /mi |
| Marathon | 3:50:01 | 3:54:16 | 8:46 /mi |
How to Use Your Predicted Paces on a Treadmill
- Set race pace by speed: each prediction shows the treadmill speed in mph and km/h; the treadmill pace converter handles any other pace.
- Add 1% incline for steady runs if you want the effort closer to running outside.
- Practice race pace in blocks: 3 x 10 minutes at marathon pace, or 5 x 1 km at 5K pace, with easy jogs between.
- Keep most runs easy: use the heart rate zone calculator to set your easy zone.
- Training at speed indoors? Check the top speed and motor in our best treadmill for running guide.
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- TitleRace Time Predictor
- PublisherFitGearHQ
- URLhttps://fitgearhq.com/running-race-time-predictor/
- Updated
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See them all on Fitness Calculators, Treadmill Tools or every free fitness tool.
Checklist Before Race Day
4 checks
Tap a number to check off that step.
- 01
Use a recent raceA result from the last two to three months reflects your current fitness.
- 02
Pick an all-out effortTraining runs or easy parkruns predict slower than you can race.
- 03
Match the trainingLong-race predictions need the long runs to back them up.
- 04
Adjust for the courseHills, heat and wind can cost minutes on race day.
Common Mistakes to Avoid
Mistake 1Predicting a marathon from a mile
Instead: The further apart the distances, the less reliable the prediction.
Mistake 2Starting at the predicted pace on a hot day
Instead: Slow down in heat and humidity, or on a hilly course.
Mistake 3Using a GPS-short course time
Instead: Check that the distance was accurate before trusting the result.
Mistake 4Racing every long run
Instead: Easy runs build the endurance that makes the prediction come true.
The Bottom Line
- Riegel: T2 = T1 x (D2 / D1)^k, with k = 1.06 by default and adjustable.
- Cameron: an alternative curve built from world-class results across distances.
- Paces per mile and per km, and treadmill speeds in mph and km/h.
- Compares you with the world records and the Boston Marathon standard for your age.
- Free to use, share, link and embed.
Frequently Asked Questions
It is usually close for nearby distances, such as 5K to 10K. From short races to the marathon, most runners finish a few minutes slower than predicted unless their long runs are well developed.
T2 = T1 x (D2 / D1)^1.06: the predicted time equals the known time multiplied by the distance ratio raised to the power 1.06.
Enter your 5K time: the calculator shows the predicted marathon and the pace to run it.
Riegel is the most widely used; Cameron is a useful second opinion that is often a little slower at the marathon.
Set the treadmill speed shown next to each prediction, and practice in blocks with easy recoveries.
Rarely. The 1:59:30 men’s record is about 13.2 mph (21.2 km/h), above the 12 mph top speed of most home treadmills; the calculator shows the treadmill speed of each record.
A hard treadmill time trial works, but set a 1% incline and check the treadmill calibration first.
