About Race Pace Predictor

Race Pace Predictor grew out of a simple frustration. Every race-time calculator we found was buried under ads, popups, and newsletter gates, and half of them wanted an account before they would show a number. We just wanted to type in a 10K and see what it meant for our marathon. So we built that.

The math behind it

The core predictor uses Riegel's formula, published by Pete Riegel back in 1981. It scales your finish time by the ratio of two distances raised to the power 1.06. It is not magic, and it assumes you have actually trained for the longer race, but for efforts within a reasonable range it holds up remarkably well.

The other calculators lean on equally well-worn methods: Jack Daniels' VDOT for training paces, age-grading standards for comparing results across ages, the Tanaka formula for max heart rate, and the running energy cost for calories. Every formula is documented in the code, and we call out where a number is an estimate rather than a hard answer.

Your data stays with you

There is no server doing the math. Every calculation runs in your browser, and your saved races live in your device's local storage. If you choose to sign in, your races sync to your own private record so you can reach them on another device, and nothing more. Signing in is entirely optional. The whole tool works without it.

No upkeep, on purpose

This is built to last. The data is static, the math does not change, and there is no database to rot or subscription to lapse. It should work the same in ten years as it does today.

Say hello

Found a bug, or think a prediction looks off? Email hello@racepredictor.run. We read everything.