Race time
predictor
Enter one recent race result and we'll predict your times and paces for the 5K, 10K, half marathon and marathon — using Pete Riegel's proven formula. Use it to set a realistic goal pace, then train to hit it.
How it works
The predictor uses the Riegel formula: T₂ = T₁ × (D₂ / D₁)1.06. The 1.06 exponent captures how everyone slows down a little as the distance grows. It's accurate up to the half marathon for well-trained runners; for the marathon, treat it as the fastest you could go on a perfect day with the endurance base to back it up.
FAQ
How does a race time predictor work?
It scales your known result to other distances with Riegel's formula (time × (distance ratio)^1.06). The exponent accounts for slowing down over longer distances.
How accurate is the Riegel formula?
Good up to the half marathon when you're well trained. For the marathon it tends to be optimistic, because the marathon rewards endurance and fueling, not just raw speed.
What is a good 5K time?
For recreational runners: sub-30 is a solid beginner goal, sub-25 is intermediate, sub-20 is advanced. Age and experience matter a lot.