Marathon Training Plan Calculator

Riegel's formula (T2 = T1 x (D2/D1)^1.06) is most accurate for well-trained runners using races within a factor of 4 in distance. Predicting a marathon from a 5K tends to be slightly optimistic; half marathon predictions are more reliable.

Most plans are 16-20 weeks for first-timers and 12-16 weeks for experienced runners. You should be able to comfortably run 15-20 miles/week before starting a plan. The longest long run is typically 20-22 miles, 2-3 weeks before race day.

Easy runs should be 1-2 minutes per mile slower than marathon pace. They should feel conversational. Most runners make the mistake of running easy days too fast, which hampers recovery and gains from hard workouts.