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Race Time Predictor

Enter a recent race result – the calculator estimates what you can run for the 5K, 10K, half marathon and marathon.

Race distance
Your time
Predicted marathon
3:50:01h
23:595K
50:0010K
1:50:19Half marathon

Predictions for all distances

Daniels performance index (VDOT): 40.0Jack Daniels' VDOT sums up your current running fitness in one number – independent of the distance. The higher, the faster. For reference: 30 ≈ a 64-minute 10K, 40 ≈ 50 min, 50 ≈ 41 min, 60 ≈ 35 min. World-class marathoners are above 80.

DistanceRiegelPace /km/miDaniels
3K13:577:2914:02
5K23:597:4324:06
10K50:008:0350:00
15K1:16:518:151:17:01
Half marathon1:50:198:251:50:52
30K2:40:138:362:40:58
Marathon3:50:018:463:49:34

How does the prediction work?

The calculator uses two proven methods. The best known is the formula by Peter Riegel, a US engineer and marathoner who published it in 1977:

T₂ = T₁ × (D₂ ÷ D₁)1.06

T₁ is your time over distance D₁, T₂ the predicted time over distance D₂. The exponent 1.06 reflects that you slow down over longer distances.

The second column is based on the formulas by Jack Daniels and Jimmy Gilbert (1979). They work out your oxygen demand from your result and derive a performance index (VDOT) that transfers to other distances. The same index powers our training pace calculator.

Examples: marathon prediction

ResultMarathon (Riegel)Marathon (Daniels)
25:00 (5K)3:59:473:57:55
50:00 (10K)3:50:013:49:34
2:00:00 (Half marathon)4:10:124:07:45

How accurate is the prediction?

Both formulas assume you're as well trained for the target distance as for the one you raced. From 5K to 10K or 10K to half marathon that usually works well. For the marathon, predictions are often too optimistic if you lack long runs and mileage. Treat the prediction as a best case and build in some buffer for your first marathon.

It's most accurate when your result is recent (no older than 4–6 weeks), was run under race conditions and the distances aren't too far apart – a half marathon predicts the marathon better than a 5K.

More calculators

SplitsPlan your splits & print a pace bandTraining PacesEasy, threshold & interval pacesHalf MarathonPace and splits for the half marathonPace ChartFinish times from 5K to marathon

FAQ

Can I predict my marathon time from my 10K?

Yes. According to Riegel, a 50:00 10K translates to a marathon of about 3:50:01. That assumes you're just as well trained for the marathon – i.e. you've done enough long runs.

Which method is more accurate – Riegel or Daniels?

They're usually close. Riegel is simpler and widely used; Daniels accounts for oxygen consumption and often gives slightly more conservative times for longer distances. If the two differ a lot, the slower time is the safer goal.

What is VDOT?

VDOT is Jack Daniels' performance index – a single number that describes your current running fitness. It's calculated from the distance and time of a race using the Daniels and Gilbert formulas. The higher it is, the faster you are – regardless of distance.