🏁 Race Predictor Time Calculator
Use a recent race result to predict your likely finish time at a different distance, based on the widely used Riegel formula.
How race time prediction works
This calculator uses Riegel’s formula, a well-established method for predicting endurance race performance across distances: T2 = T1 × (D2 / D1)^1.06, where T1 and D1 are the time and distance of a recent race, and D2 is the distance you want a prediction for. The exponent 1.06 accounts for the natural slowdown in pace as distance increases, based on decades of race data across running events.
How to use it
Enter the distance and finish time from a recent race you’re happy represents your current fitness, then enter the distance you want to predict. The calculator returns an estimated finish time and pace for the new distance.
Predictions work best when the two distances aren’t too far apart (for example, using a 5K to predict a 10K is more reliable than using a 5K to predict a marathon) and assume similar course, weather, and pacing conditions. Actual results depend on training, terrain, and race-day factors, so treat this as a planning guide rather than a guarantee.