Tool
Race time predictor
What could you run a half marathon in if you can do 10K in 48 minutes? Enter a race you have run and get an estimate for 5K, 10K, half marathon and marathon.
How the prediction works
The prediction uses Riegel's formula, which describes how pace drops as the distance grows: T2 = T1 × (D2 ÷ D1)1.06. T1 and D1 are the time and distance of the race you ran, D2 the distance you want a time for.
Example: 10 km in 48:00 gives about 23:01 for 5 km, 1:45:54 for a half marathon and 3:40:49 for a marathon.
How far can you trust it?
- It is best for distances close to the race you start from, for example from 10K to a half marathon.
- It assumes you have trained for the longer distance. Without long runs the marathon prediction is often too fast.
- Start from a recent race you ran all out, on a course without big hills.
To turn a goal time into a pace per km, try the pace calculator.
Common questions
Common questions about the prediction
How accurate is the prediction?
It is an estimate. For distances close to your race it is usually close, but it assumes you have trained for the distance.
Why is the marathon prediction often too fast?
A marathon needs endurance that shorter races don't measure. Without long runs and enough training, most people slow down more than the formula expects.
Which race should I start from?
A race you ran all out in the last few months, ideally on a flat course. A half marathon gives a better marathon prediction than a 5K.
Is anything I type stored?
No. Everything is calculated in your browser and nothing is sent or stored.
Want to reach that time?
TriQuest builds a training plan for your race, from 5K to marathon, around your week.