PredictMyRun uses Riegel's formula, a proven method for predicting running times across different distances. Developed by Peter Riegel in the 1970s and published in Runner's World, this formula has become the standard for race time predictions.

The Formula

Where:

• T₁ is your known time for a given distance
• D₁ is your known distance
• T₂ is your predicted time
• D₂ is your target distance
• The exponent 1.06 accounts for fatigue as distances increase

Riegel's formula is based on the observation that as running distance increases, pace typically slows down in a predictable pattern. The formula uses a power law relationship to model this pattern, allowing for accurate predictions across a wide range of distances.

Example Calculation

If you ran a 5K (5 kilometers) in 25:00 (1,500 seconds), your predicted 10K time would be:

While Riegel's formula is remarkably accurate for many runners, it's important to understand its limitations:

• Individual variations: Factors such as training specificity, experience level, and personal strengths can affect your actual performance.
• Race conditions: Weather, terrain, elevation, and course profile are not accounted for in the formula.
• Distance extremes: The formula is most accurate when predicting between distances that aren't too far apart (e.g., 5K to half marathon).
• Speed vs. endurance athletes: Sprinters and ultra-marathoners may see less accurate predictions due to their specialized adaptations.

For best results, use a recent race time or time trial as your known performance, and update your predictions as your fitness changes.

Understanding your predicted times across different distances can help you:

• Set realistic race goals based on your current fitness level
• Identify strengths and weaknesses in your performance across distances
• Plan appropriate training paces for different workout types
• Track your progress as your fitness improves

Coaches and serious runners often use these predictions as benchmarks to assess if an athlete is underperforming at certain distances, which may indicate training needs or race strategy adjustments.

Peter Riegel, an engineer and runner, first published his formula in Runner's World magazine. Since then, it has been validated by numerous studies and adopted by coaches worldwide.

Research has shown that the exponent 1.06 works well for most recreational and competitive runners, though elite athletes may have slightly different values based on their exceptional training and physiology.

Alternative prediction methods exist, such as the Cameron method and VO2max-based calculations, but Riegel's formula remains the most accessible and widely used due to its simplicity and reliability.