Marathon Time Predictor
Standard predictors use the Riegel formula and run too fast for the marathon, because they ignore how many miles you actually train. This predictor corrects for that: it raises the fatigue exponent as weekly mileage drops, so a 20 mile per week runner gets a realistic time, not an optimistic one.
Enter a recent race result and your typical weekly mileage to get a marathon prediction, the uncorrected Riegel time for comparison, and your target marathon pace.
Raise your mileage
Zone 2 Running Guide
Aerobic base volume is the strongest trainable predictor of marathon performance. Build it the right way.
Fuel the distance
Carb Loading Calculator
Hitting your predicted time means starting with full glycogen. Plan the 36-hour load to the gun.
Marathon time predictor FAQ
How accurate is a marathon time predictor?
A predictor is only as good as its inputs. The standard Riegel formula is accurate up to the half marathon but tends to predict the full marathon too fast, because it cannot see how much endurance training you have done. One study of recreational runners found the basic formula gave marathon times at least 10 minutes too fast for half the field. Correcting for weekly mileage closes much of that gap, which is what this tool does.
Why does weekly mileage change my predicted marathon time?
The marathon is decided in the final 10 kilometers, where runners who lack aerobic volume slow down sharply. Two runners with the same half-marathon time but different training mileage will not run the same marathon: the higher-mileage runner holds pace while the lower-mileage runner fades. This calculator raises the fatigue exponent as weekly mileage drops, so a 20 mile per week runner gets a more realistic, slower prediction than a 55 mile per week runner off the same race.
What is the Riegel formula?
The Riegel formula predicts a race time at one distance from a known time at another: T2 equals T1 times the distance ratio raised to the power of 1.06. The exponent of 1.06 represents how much you slow down as distance increases. It works well for nearby distances but underestimates the marathon for most recreational runners, which is why this tool adjusts the exponent based on your training volume instead of using a flat 1.06.
Which race should I use to predict my marathon?
Use the longest recent race you have, ideally a half marathon. The closer the predictor distance is to 26.2 miles, the more reliable the prediction, because it captures more of the endurance demand. A 10K is usable, and a 5K gives a rough ceiling, but both will read optimistically for the marathon unless your weekly mileage is high. Run the race within the last few weeks and on a course similar to your goal race for the best read.
Can I beat my predicted marathon time?
Yes. A prediction reflects your current fitness and training volume, not your ceiling. The fastest way to improve the number is to raise your weekly mileage over a training block, since aerobic volume is the strongest trainable predictor of marathon performance. Consistent easy running, a weekly long run, and disciplined pacing on race day, especially avoiding a fast first half, all move your actual time toward or past the prediction.
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