Race time predictor
Enter one recent race to see what it predicts from the mile to the marathon, with two classic formulas side by side and a marathon prediction adjusted for how much you run.
Add your typical weekly mileage for a marathon prediction that accounts for how much you train.
Every distance
How the predictions work
The Riegel column uses the formula Peter Riegel, a research engineer, published in Runner’s World in 1977 and expanded in American Scientist in 1981. Your new time is your old time multiplied by the ratio of the two distances raised to the power of 1.06, and Riegel framed it for efforts lasting roughly 3.5 to 230 minutes (Wikipedia).
The VDOT column turns your race into Jack Daniels’ VDOT fitness score, then works out the time that score predicts at each distance. The VDOT calculator shows the training paces that go with it.
Why marathon predictions run fast
Both formulas assume you’ve trained for the distance you’re predicting, and for most recreational runners that holds up far better at the half marathon than at the marathon. When Andrew Vickers and Emily Vertosick of Memorial Sloan Kettering checked predictions against 2,303 recreational runners, the Riegel formula worked reasonably well up to the half marathon but gave marathon times at least 10 minutes too fast for half of them (Vickers and Vertosick, 2016).
Their fix was to add typical weekly mileage, which was strongly tied to marathon times, and the resulting model was far better calibrated than Riegel’s. The mileage-adjusted marathon prediction above uses their published one-race model, which starts from a Riegel prediction and adjusts it for how much you run. It works from a 5K, 10K or half marathon.
Getting the most accurate prediction
Use the longest race you’ve run recently. For a marathon, Greg McMillan suggests racing a half marathon, or anything from 15K to 30K, at least three weeks out and ideally four or five, then using that result (McMillan Running). His shortcut for the conversion is to double your half marathon time and add seven minutes.
Use an all-out effort in normal conditions. A hot day, a hilly course or a race run as a workout will make every prediction too slow, and a downhill course will make them too fast.
Treat the number as a starting point. The marathon pace chart and the goal pages turn whatever goal you settle on into splits, and the average marathon time guide shows how it compares with the rest of the field.
