About this calculator
This is a (beta) race time predictor which takes into account your sex and whether you are best at short or long races. It starts with the Riegel formula and then weights your result.
The Riegel formula is a widely used method for predicting race times across different distances, but it has limitations. It assumes a consistent endurance profile and a fixed fatigue factor, which may not reflect individual variations in training, pacing strategy, or physiological strengths. As a result, it tends to be less accurate for very short races (e.g., 5 km) where speed rather than endurance dominates, for ultra-distances where cumulative fatigue plays a larger role, or for athletes whose strengths are highly distance-specific.