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Race Predictor Calculator

Estimate your finish time at other distances from a recent race result — shown as an interval from two independent models.

Race Predictor

Enter a recent race result to predict equivalent finish times at other distances using two independent models.

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Prediction models

RiegelPeter Riegel · 1977

Originally published in Runner’s World. The formula T₂ = T₁ × (D₂/D₁)^1.06 gives accurate results for race durations between 3:30 min and 3:50:00 h. Outside that window, extrapolations become less reliable.

CameronDavid F. Cameron · 1998

Derived from nonlinear regression on world-record performances from 400 m to 50 miles. Uses a distance-specific fatigue factor: T₂ = T₁ × (D₂/D₁) × f(D₁)/f(D₂) where f(d) = 13.497 − 0.0000304d + 835.7/d^0.79. Tends to be more conservative than Riegel for longer target distances.

Predicted finish times

5KYour time

20:00

10K

41:40–41:42

Riegel41:42(slower)Cameron41:40(faster)
Half Marathon

1:31:51–1:32:00

Riegel1:32:00(slower)Cameron1:31:51(faster)
Marathon

3:11:49–3:15:11

Riegel3:11:49(faster)Cameron3:15:11(slower)

Reading the interval

Each card shows a time range spanning both models. For a longer target race, Riegel is the optimistic bound and Cameron is the conservative one. For a shorter target, the roles reverse.

Training paces

VDOT 49.8

Derived from the race you entered using the Jack Daniels VDOT method. For more accurate marathon-pace training, enter a marathon result instead.

Easy
4:54–5:53/km

Conversational long runs and recovery. Builds aerobic base.

Marathon
4:26–4:51/km

Goal marathon race pace. Sustained medium-long runs.

Threshold
4:16–4:28/km

Comfortably hard tempo runs and cruise intervals.

Interval
3:51–4:01/km

Hard 3–5 min repeats to maximise VO₂max stimulus.

Repetition
3:34–3:42/km

Short 200–400 m reps at mile effort with full recovery.