Tools › Pace calculator and race time predictor
RunningYour pace from a recent race, and predicted 5K, 10K, half and marathon times. Runs in your browser; nothing is saved or sent.
The predictions use the formula most often credited to Peter Riegel, who analyzed endurance records (Riegel, 1981) and found race time rises a little faster than distance. The commonly used version is predicted time = your time × (new distance ÷ your distance)1.06. The exponent differs a little between groups of athletes: Vickers & Vertosick (2016) report that Riegel cited about 1.08 for elite runners and 1.05–1.06 for male recreational runners aged 40 to 70, and that the Runner’s World online calculator uses 1.06.
How accurate is it? In a study of 2,303 recreational runners (Vickers & Vertosick, 2016), the formula was well calibrated (close to real results on average) for predictions up to the half marathon, but it predicted marathon times at least 10 minutes too fast for half of the runners. So for the marathon, plan on a buffer: in that study the formula predicted a faster marathon than most of these runners ran.
General information for healthy adults, not medical advice. If you have a medical condition, are pregnant, or are new to running, build up gradually and talk to a doctor before racing.