Good Run Guide

Find a Race


Our Race Time Predictor is based on the widely respected "Riegel Formula", developed by Peter Riegel and first published in 1977. We have used linear regression techniques to customise the formula to take account of race data from your Log Book.


Race Time Predictor

Predict your finish time for a race by using the calculator below.

The calculator uses a recent race you have run as a guide and makes an assumption about how increases in distance affect your speed in order to calculate a "Performance Degradation Factor". If you are a Good Run Guide Member, you can use a custom Performance Degredation Factor based on selected races from your Log Book, which should generally result in more accurate predictions. The more races of the same type you have logged, the more accurate the prediction is likely to be but please bear in mind that your actual time on the day will be also be influenced by other factors such as variations in terrain, weather, hilliness and how you feel.

STEP 1 - How long is the race you plan to run?
Enter here the length of the race you plan to run. RACE LENGTH (5K to marathon only)
STEP 2 - Enter your finish time for a recent race (between 5K and marathon)

Select a race where your finish time reflects your current performance level and where the race is of a simailar type (hilliness and terrain) to the one you plan to run, as this will improve the accuracy of the prediction (i.e. don't choose a hilly cross-country race if you are predicting a time for a flat road race).

FINISH TIME (hh:mm:ss) : :



STEP 3 - Choose a Performance Degradation Factor
Please login to select past races from your Log Book to use in the prediction

This factor reflects your ability to maintain your average speed as the length of the race increases. This varies for different types of runners. Ultra-distance runners tend to have very low factors (as low as 3%) while sprinters have very high factors (as high as 30%). Our suggested default value is 8% - in rough terms, this means that your speed declines by about 8% when the distance doubles.

Use default (8%)  
Estimate from my Log Book (n/a) *
Use this value %  

* If you use the Good Run Guide Log Book, we can analyse races you've logged to estimate your Performance Degradation Factor.

STEP 4 - Your predicted finish time for the race
PACE :  


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