Running Race Predictor & Pace Calculator
Enter a recent race or hard training run. We’ll predict your finish time, and the pace you’ll need to hold, for your next race.
Predicted finish time
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Ready to train for that time?
Give TextFit’s AI coach your race and date and a recent result in your own words. It plans the weeks to race day and puts every session on your Garmin or Apple Watch with paces in your numbers.
14 days free, then $14.99/month or $99.99/year. Cancel anytime in your App Store or Google Play settings.
How the prediction works
The calculator uses Riegel’s formula, the endurance model most running
race predictors are built on: T2 = T1 × (D2 ÷ D1)1.06. It takes
your recent time (T1) over a known distance (D1) and scales it to the target distance
(D2), with the 1.06 exponent accounting for the pace runners naturally lose as races
get longer.
For the best prediction, use a recent all-out run — ideally from the last couple of months and at a distance not too far from your goal race. A 10K or half marathon result predicts a marathon far better than a 5K does, and the formula assumes you’ve done the endurance training the longer distance demands.
Have a goal time now? The 16-week marathon training plan lists the pace per km and per mile for finish times from 3:00 to 5:00 and shows, week by week, where to practise it. For 21.1 km there is the 12-week half marathon training plan, and if your prediction is close to two hours, the sub 2 hour half marathon training plan with its 5:41 per km goal pace, splits and readiness table.