Race time predictor
Turn one recent result into estimated times for other distances.
How does the race time predictor work?
It uses the Riegel formula: the new time equals the old time multiplied by the distance ratio, raised to the power 1.06. The exponent says you slow down a little as the distance grows.
Use a recent, all-out result, such as a 5K or 10K race. A comfortable training run will predict times that are too slow.
How accurate is it?
It is an estimate. It works best for a runner who has trained for the longer distance, and it tends to be too fast for a first marathon, because endurance matters more than speed over 42 km. Heat, hills and the course change the real result. Treat the table as a range to aim for, not a promise.
Frequently asked questions
Which race should I enter as my recent result?
Use a hard, recent effort over 5K to a half marathon. The closer it is to your target distance, the better the estimate.
Why is my marathon estimate so fast?
The formula assumes marathon training. Without long runs, most people finish slower than predicted. Add a margin, or use the pace chart to plan a cautious first half.
Does it work in miles?
Yes. Switch the units, then enter the distance in miles. The results show pace per kilometre or per mile to match.