Race Time Predictor Formula

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

Use the Race Time Predictor

Formulas Used

Predicted Hours

predicted_hours = floor(predicted_time_min / 60)

Predicted Minutes

predicted_minutes = floor(predicted_time_min - floor(predicted_time_min / 60) * 60)

Predicted Seconds

predicted_seconds = round((predicted_time_min - floor(predicted_time_min)) * 60)

Predicted Pace

predicted_pace = predicted_time_min / target_distance_miles

Variables

VariableDescriptionDefault
known_distance_milesKnown Race Distance(miles)3.1
known_time_minKnown Race Time(min)25
target_distance_milesTarget Race Distance(miles)13.1
predicted_time_minDerived value= known_time_min * pow(target_distance_miles / known_distance_miles, 1.06)calculated

How It Works

How the Riegel Race Prediction Formula Works

The Riegel formula predicts race times across distances based on a known performance.

Formula

T2 = T1 x (D2 / D1) ^ 1.06

Where:

  • T1 = Known race time
  • D1 = Known race distance
  • D2 = Target race distance
  • 1.06 = Fatigue exponent

    • The formula works best for distances between 1500 m and the marathon, assuming similar fitness and training for both distances.

    Worked Example

    You ran a 5K (3.1 miles) in 25 minutes and want to predict your half marathon time.

    known_distance_miles = 3.1known_time_min = 25target_distance_miles = 13.1
    1. 01Distance ratio = 13.1 / 3.1 = 4.2258
    2. 02Fatigue factor = 4.2258 ^ 1.06 = 4.6013
    3. 03Predicted time = 25 * 4.6013 = 115.03 minutes
    4. 04That is 1 hour, 55 minutes, and 2 seconds
    5. 05Predicted pace = 115.03 / 13.1 = 8.78 min/mile

    Ready to run the numbers?

    Open Race Time Predictor