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Race time predictor

One result you have already run, turned into what it is worth at 5K, 10K, the half and the marathon.

What have you run?

Kilometres. Used when Other is selected.

What did you run it in?

A recent, honest effort — a race or a hard time trial.

Where the numbers come from

Pete Riegel's endurance formula, published in 1981 and still the one most calculators use: T₂ = T₁ × (D₂ / D₁)^1.06. A time over one distance, scaled by the ratio of the distances raised to 1.06 — a little more than linear, because nobody holds 5K pace for a marathon.

It is a curve fitted to record performances, and it knows one thing: the time you gave it. It does not know how many long runs you have done, and it assumes you are equally trained for both distances — so it over-predicts across a big jump and for anyone who has not put the volume in. Treat a marathon predicted from a 5K as a ceiling.

For a plan that would get you there, the training plan generator starts from the same kind of time trial.

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