Finish Time Prediction Calculator

Work out finish time prediction instantly with clear inputs, formula shown and shareable results.

About Finish Time Prediction Calculator

Riegel's formula predicts race times as T2 = T1 x (D2/D1)^1.06, where the exponent above one captures the inevitable slowdown over longer distances. A 48 minute 10 km projects to about 1:40:00 for a half marathon, roughly 16 seconds per kilometre slower. Poorly conditioned runners need an exponent nearer 1.10 for the marathon.

Formulas

Riegel prediction

T2 = T1 x (D2 / D1)^1.06

Exponent

1.06 for trained runners, up to 1.10 without endurance base

Worked example

With the default values below, Finish Time Prediction Calculator returns Predicted Time of 105.91. Change any input above and every figure here is recalculated in your browser.

Inputs used

Distance you have racedminimum 0.1 km: 10 km
Time for that distanceminimum 0.1 min: 48 min
Distance you want to predictminimum 0.1 km: 21.0975 km
Riegel fatigue exponentaccepts 1–1.3: 1.06

Results

Predicted Time: 105.91 min
Predicted Time As h:mm:ss: 1:45:54
Predicted Pace Per Kilometre: 5:01
Pace Slower Than The Known Race By: 13.2 s/km

Step by step

1Values used
2Riegel prediction
3Exponent
4Predicted Time= 105.91 min
5Predicted Time As h:mm:ss= 1:45:54
6Predicted Pace Per Kilometre= 5:01
7Pace Slower Than The Known Race By= 13.2 s/km

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
This is an estimate from population-average equations, not a medical or diagnostic assessment. Individual results vary with genetics, training history and technique. Seek advice from a qualified coach or clinician before making significant changes to training.
This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

This is an estimate from population-average equations, not a medical or diagnostic assessment. Individual results vary with genetics, training history and technique. Seek advice from a qualified coach or clinician before making significant changes to training.

Frequently Asked Questions

How well does this work for the marathon?

It tends to be optimistic, because the marathon exposes fuelling and durability limits that shorter races do not. Adding 2-5% is realistic without high mileage.

Can I predict shorter from longer?

Yes, the formula works both ways, and it is generally more reliable downwards than upwards.