Endurance calculator
Race time predictor
Enter a race you've run and predict your finish time at any other distance — plus the pace you'll need to hold. Free, instant, no sign-up.
Get a training plan built around this goal — the coach remembers it and adapts each week.
What is a race time predictor?
It takes a race result you already have — say 5K in 25 minutes — and estimates what you'd run at another distance, like a 10K or a half marathon. It's the fastest way to set a realistic goal pace without racing every distance first.
How this calculator works
We use Riegel's formula: predicted = known time · (target distance / known distance)1.06. The 1.06 exponent captures fatigue — pace fades as distance grows, so you can't hold your 5K pace for a marathon. It's accurate within a few-fold of your known distance and drifts when extrapolating far beyond it.
Using the prediction
Treat the pace per km as your target race pace, then train a little faster on intervals and a little slower on easy runs. A prediction is only a ceiling on race day — the work between now and then is what gets you there. Want that work programmed into a week that adapts as you improve? That's what the coach is for.