Marathon Time Predictor Formula

Understand the math behind the marathon time predictor. Each variable explained with a worked example.

Use the Marathon Time Predictor

Formulas Used

Predicted Marathon Time (min)

marathon_time = race_time_minutes * pow(marathon_distance / race_distance, 1.06)

Marathon Time (hours)

marathon_hours = race_time_minutes * pow(marathon_distance / race_distance, 1.06) / 60

Predicted Pace

marathon_pace = race_time_minutes * pow(marathon_distance / race_distance, 1.06) / 26.2

Variables

VariableDescriptionDefault
race_time_minutesRecent Race Time(minutes)25
race_distanceRace Distance(miles)3.1
marathon_distanceDerived value= 26.2calculated

How It Works

Riegel Formula

Predicted Time = Race Time x (Target Distance / Race Distance)^1.06

The Riegel formula, developed by Peter Riegel in 1977, accounts for the fact that pace slows as distance increases. The exponent 1.06 captures this endurance fatigue factor.

Worked Example

A runner who completed a 5K (3.1 miles) in 25 minutes.

race_time_minutes = 25race_distance = 3.1
  1. 01Marathon distance = 26.2 miles
  2. 02Distance ratio = 26.2 / 3.1 = 8.452
  3. 03Predicted time = 25 x 8.452^1.06
  4. 04= 25 x 9.55 = 238.7 minutes
  5. 05= 3 hours 58.7 minutes
  6. 06Pace = 238.7 / 26.2 = 9.11 min/mile

Frequently Asked Questions

How accurate is the Riegel formula?

The Riegel formula is reasonably accurate for well-trained runners. It may overestimate for beginners and underestimate for elite runners.

Does training matter?

Yes. This prediction assumes you train adequately for the marathon distance. A 5K time alone does not guarantee marathon performance without proper long-run training.

Learn More

Guide

Running Pace Calculator Guide: How to Find and Improve Your Pace

Learn how to calculate running pace, understand pace vs. speed, set race targets, and use pace training to improve your performance at every distance from 5K to marathon.

Ready to run the numbers?

Open Marathon Time Predictor