Why use 1.07 instead of 1.06 for ultras?

Ultra distances involve significantly more fatigue than standard road races. A slightly higher exponent (1.07) accounts for the additional factors like sleep deprivation, nutrition challenges, and terrain difficulty that affect ultra performance.

How accurate are ultra predictions?

Ultra predictions have more variability than shorter distance predictions due to terrain, elevation, weather, and nutrition factors. Use these as rough estimates and adjust based on the specific course profile.

What marathon time for a sub-24 hour 100 miler?

A sub-24-hour 100 miler typically requires a marathon time under 3:30-3:45, though ultra-specific training and experience are equally important.

RunCalcs

Ultra Predictor — Predict Ultra Marathon Times

Predict ultra marathon times for 50K, 50 mile, 100K and 100 mile from marathon or half marathon results.

Known Race

Ultra Distance

Hours

Minutes

Seconds

How We Calculate This

Ultra Prediction Formula

T2 = T1 × (D2 / D1)^1.07

The exponent is increased to 1.07 for ultra distances to account for the additional fatigue factors unique to ultramarathons.

Ultra distances: 50K = 50 km, 50 miles = 80.467 km, 100K = 100 km, 100 miles = 160.934 km.

Frequently Asked Questions

Related Calculators

Marathon Time Predictor

Predict your marathon time from a shorter race result.

Half Marathon Predictor

Predict your half marathon time from 5K or 10K results.

10K Predictor

Predict your 10K time from a 5K or parkrun result.

5K Predictor

Predict your 5K time from shorter or longer race results.

Parkrun Predictor

Predict your parkrun time from other race distances.

Last updated: February 2026

All calculations are estimates. Always consult a coach or medical professional for personalised training advice.