Race Time Prediction
Calculator

It typically applies a formula like Riegel's, which scales a known time at one distance to another distance using an exponent that accounts for endurance loss over longer efforts. Feed it a recent race result and it estimates your time at the target distance.

Endurance events don't scale linearly with speed; the body fatigues more per kilometer as distance increases. The prediction formula applies a fatigue factor so the estimate is realistic rather than overly optimistic.

No, it's based purely on your input performance and distance, assuming similar conditions and effort. Hot weather, altitude, or a hilly course can all make the actual result slower than the prediction.

Use a race or time trial from the last few months at a similar fitness level for the best accuracy. An old personal best from a year ago will overestimate your current fitness and give an unrealistic target.

Each distance stresses a different mix of speed and endurance, so a strong 5K doesn't guarantee proportional marathon endurance, and vice versa. Predictions from a race closer in length to the target distance are generally more reliable.