Race Time Predictor

How does it work

You want to estimate your next race time? Here is the perfect tool for you. This race time estimator is based on the Riegel formula, which is the most popular formula for race time estimation. I highly recommend you to read below text to better understand the functionning and the limits of the predictor. If you want to know more about how to predict a race time, check the dedicated article.

Race Time Estimator
Kilometers
Miles

Overview of Riegel Formula

The Peter Riegel formula is one of the most widely used methods to estimate running race times. Developed by Peter Riegel, an engineer and marathon runner, this formula was introduced in a 1977 article in Runner’s World. It provides a simple yet effective way to predict how you might perform in a race based on your result from another distance. The formula is expressed as:

Time₂ = Time₁ × (Distance₂ ÷ Distance₁)^1.06

This equation calculates your estimated time for a future race (Time₂) based on your time for a known distance (Time₁). It assumes a logarithmic relationship between speed and endurance, meaning performance declines more gradually as distances increase.

How to Use the Riegel Formula

Using the Riegel formula is straightforward, even for beginners. Here’s an example:

  1. Suppose you recently completed a 10K race in 50 minutes.
  2. You want to predict your time for a half marathon (21.1 kilometers).
  3. Insert your values into the formula:
    50 × (21.1 ÷ 10)^1.06 = 1 hour and 50 minutes.

Tools like online race time predictors make it even easier to use the Riegel formula. Simply input your previous race time and distance, and let the calculator handle the math for you.

Assumptions and Limitations of the Riegel Formula

The Riegel formula is based on a few important assumptions:

  1. Consistent Effort: It assumes you’re running with the same level of effort and pacing across both distances.
  2. Training Level: The runner must be well-trained for both distances.
  3. Similar Conditions: Factors like weather, terrain, and altitude should be comparable between races.

However, the formula has limitations. It tends to overestimate the time for short and long distances: The formula often predicts overly optimistic times for very short efforts (< 5 min) or longer races (> 4 hours), such as marathons, where fatigue becomes a more significant factor. Additionally, it does not account for individual variability, such as recovery ability, training history, or pacing skills.

Despite these limitations, the Riegel formula is a proven and effective tool for most runners, offering valuable insights into potential performance and helping athletes prepare smarter.