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Race Time Predictor

Race Time Predictor

Would you like to know how fast can you run your first half marathon?

The race time predictor can predict the result of a targeted race based on previous race results.

What can we calculate using the race time predictor?

The race time predictor can estimate the result of the desired race and calculate the average pace you will need based on the results of previous races or runs.

I will show you how to use the race time predictor to estimate the time of a future race, who the predictor is for, and how it actually works.

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Race Time Predictor

How to estimate race time using the race time predictor?

  1. Choose your most recent race from the options.
  2. Input the time of your last race.
  3. Choose the desired race from the options.
  4. If your desired race is a marathon it is advisable to input the number of miles/kilometers you run on a weekly basis.
  5. The predictor will calculate the time of your desired race and the average pace of that race.

Race time predictor assumptions

Before using the race time predictor, it is important to be aware of certain assumptions tied to the tool:

It is assumed the runner has done the appropriate training for the distance he wants to run.

If you’ve run an excellent time on your 10K race yesterday that does not mean that you will be able to run a half-marathon in the desired time today. Appropriate rest is needed between races.

Table of times calculated by the race time predictor

The table shows the times of the most common races given by the race time predictor using the Riegel formula.

As can be seen from the table, there are no calculated times for a marathon. This is due to the Riegel formula’s inaccuracy for results longer than 4 hours. If you wish to calculate the time of your next marathon you should use the race time predictor.

How to use the table?

Find the time closest to the result time of your most recent race and in that row, you will find the calculated times for other races.

1500m1mi3K5K5mi10K10miHalf marathon

Who is the race time predictor for?

The race time predictor is a tool intended for all those who wish to know their potential results for races of different lengths.

If you wish to set a personal record you will have to figure out the pace for a particular race. A perfect race has the lowest possible amount of pace changes, which is why the race predictor calculates the average pace as well. This way you will avoid running too quickly in the earlier stages and exhausting yourself early.

Race Time Predictor

How does the race predictor actually work?

The formula used by the race predictor for calculating race times, for races shorter than a marathon, is based on a formula developed by Pieter Riegel, a scientist and marathon runner, in 1977.

The formula allows for an estimation of a result time for the desired race based on the results of a previous race.

Due to its high accuracy and simplicity, over the years the Riegel formula has become the definitive way for predicting race times.

Riegel formula:



  • D₁ (last race) – distance covered in the time of T₁
  • D₂ (desired race) – distance to be covered in the time of T₂
  • T₁ (time of last race) – recently achieved time over the distance of D₁
  • T₂ (estimated race time) – estimated time needed to cover the distance of D₂

One downside of the Riegel formula is its inaccuracy in calculating times shorter than 3.5 minutes and longer than 4 hours. As a result, a race time predictor uses an improved Riegel formula developed by Andrew Vickers to calculate marathon times. To learn more about the improvements to the Riegel formula when it comes to calculating marathon times click here.

Weekly mileage is a key factor for calculating marathon times, which is why the improved formula uses this variable (Mi/Km per week).

To be able to run the desired time you have to know the pace at which you will be running. This is why the race time predictor calculates the average pace for your race as well.


Matea Matošević

Hi, I’m Matea! I’m an Olympic Marathon Runner, founder, and writer behind OLYRUN.com. On this site, I provide help in the form of my knowledge and experience to all who love running and active living. Read more…