Ultra Pacing Calculator

About this calculator

Predicting an ultramarathon finish time from a known shorter race result relies on scaling that result up with a fatigue factor, extending the same logic behind race-prediction formulas like Riegel's (which uses an exponent, typically around 1.06 for standard road distances, to model the fact that average pace slows as race distance increases) but applying a larger exponent or additional adjustment for ultra distances, where fatigue, fueling and terrain accumulate far beyond what a marathon-based model captures.

Ultrarunners moving up from marathon or shorter ultra distances use this kind of prediction to set an initial goal pace for a new, longer distance they haven't raced before, giving a data-grounded starting point rather than a guess, which then typically gets refined further with course-specific factors like elevation and terrain. It's especially useful for choosing an opening pace conservative enough to avoid blowing up in the second half of a long race.

This calculator takes a known race result (distance and time) and your target ultramarathon distance, and returns your predicted finish time and average pace, adjusted with a fatigue factor for the longer distance.