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.
Keep this pace on file — watch it drop as training lands.
Free — no card, 30 seconds. Your result comes with you.
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 half marathon. It's a fast 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 exponent captures fatigue — pace fades as distance grows. It works best near your known distance and drifts when extrapolating far beyond it.
Using the prediction
Treat the pace 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 gets you there. The coach can program that work into an adaptive week.