Race Time Predictor

Courtesy of Runners World Magazine

This calculator lets you input an actual race time to see what you should be capable of at another distance. It is adjusted for distance (ie its 10K prediction isn't just double your 5K time), but there are three caveats:

1. It assumes you've done appropriate training for the distance. Doing a 22-minute 5K today doesn't mean you can do a sub-4 marathon tomorrow. Obvious, really.
2. It assumes you don't have a natural significant bias towards either speed or endurance. Some people, no matter how much training they do, will always over-achieve at one end of the scale.
3. The calculations become less accurate for times under three and a half minutes and over four hours.
4. My own view is that I wouldn't regard it as being too accurate if I were you, especially if you are comparing a relatively short existing time against a projected future longer distance (e.g. your recent 10k time to predict your likely marathon time). I'd add a bit on top of the predicted time for those races which might be stretching the calculation a bit, to allow for general tiredness over the longer distance, lack of energy reserves etc.

The formula was originally devised by Pete Riegel, a research engineer and marathoner, and published in Runner's World, most recently by Owen Anderson in 1997. It has been widely used since then. The formula is T2 = T1 x (D2/D1)^1.06 where T1 is the given time, D1 is the given distance, D2 is the distance to predict a time for, and T2 is the calculated time for D2.