Race Predictor Calculator
Use a recent race result to predict your finish time for a different distance, using the widely used Riegel formula.
What this calculator does
It predicts how fast you could run a new race distance based on a recent, honest race effort at a different distance — a useful way to set a realistic goal time for an upcoming race.
The formula
This calculator uses the Riegel formula, a widely used endurance performance model published by Peter Riegel in 1977: T2 = T1 × (D2 ÷ D1)1.06, where T1 and D1 are your known time and distance, and T2 and D2 are the predicted time and target distance. The exponent of 1.06 reflects the fact that pace naturally slows somewhat as distance increases, due to fatigue and endurance limits.
The Riegel formula works best when comparing races of reasonably similar type (for example, a 10K to a half marathon) and tends to be less accurate across very large jumps in distance, such as predicting a marathon from a 5K, since marathon performance depends heavily on endurance-specific fueling and pacing beyond pure fitness.
For general training and goal-setting purposes only.