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Race Time Calculator: Predict Your Race Finish Times

Welcome to Marathon Handbook’s running race time prediction calculator.

Tell us how fast you ran a previous race, and we’ll give you predicted race times for all common race distances from 5k to 200 miles.

Our race time calculator displays the results from two common prediction methods side-by-side. Keep scrolling past the calculator to see a breakdown of how each formula works and its limitations.

The predicted race times given are the predicted times assuming you have trained appropriately for said distance. For example, the half marathon predicted time is an estimation of how fast you would run a half marathon if you were properly trained for this distance.

It’s important to note that the race time predictions will be most accurate for the distances closest to the previous race distance you entered. For example, if the previous race time you inputted is for a 7km race, then the 10km and 5km race time predictions are likely to be more accurate than the half marathon and marathon predictions.

It’s important to note that whilst the formulas in the race time calculator tend to be accurate from 5k to half marathon distances, they tend to underpredict race times for distances beyond this.

You can check out our specific advanced marathon race time predictor for a more accurate marathon race time prediction based on previous race time and weekly training mileage.

Additionally, you can check out our age-grade calculator to predict race times and compare your score with other runners and world record holders at the same time.

Race Time Predictor

Please enter how fast you ran a previous distance to calculate your predicted race times.


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*Please enter your time in the format hh:mm:ss.

Predicted Times

Distance Pete Riegel Formula Prediction David Cameron Formula Prediction
a lady running on top of a rocky hill with a sunset and view behind. She is wearing headphones.

Pete Riegel Formula Explained

This race time prediction formula was proposed by Pete Reigel in 1977 and published in Runner’s World magazine. It has been hugely popular since then due to its simplicity and relative accuracy.

Based on a study of how the pace of elite runners decreases with distance, the Riegel formula proposes says that a person’s speed declines by around 6% when the distance doubles.

David Cameron Formula Explained

As opposed to a linear formula, David Cameron used a number of times of world-level athletes from 400M to 50 Miles in a non-linear regression model to develop a formula to predict race times. 

Whilst more complex, this is an effective method, as running pace does not decrease in a fully linear fashion as distance increases.

Formula Limitations

One issue with the formulas used in the above race time calculator is that they tend to be based on the race times of professional runners, meaning they are often inaccurate when used to predict the race times of recreational distance runners.

For example, the world record time for the half marathon is 57:31, and the world record for the marathon is 2:01:09, meaning that both races are run at a similar pace.

Yet, the average runner, who hasn’t had access to professional training, is more likely to run a marathon at a notably slower pace than a half marathon.

Therefore, this means the race time predictions given by these formulas for distances greater than a half marathon may be underpredicted by ten minutes or more.

To get a more accurate marathon time prediction, check out our advanced marathon time calculator.

Other Factors Affecting Race Time

Data from Fetch Everyone suggests that runners who have a faster marathon pace tend to run slower than their marathon pace during training, but runners with a slower pace tend to run faster than their marathon pace during training.

Furthermore, more experienced runners (i.e. those who have a better half-marathon time, and who are able to run higher weekly mileage and train with longer long runs without the risk of overtraining) are more likely to run their race faster than the prediction given by the two above formulas.

On the other hand, for less experienced runners, the formula is more likely to underpredict their race time, meaning that individuals are more likely to run slower on race day than their predicted time.

This is a very important fact to remember. It means that if you achieve a race time slower than the prediction given to you by the race time calculator, it does not mean you have failed your target in any way, but rather it is likely due to the formula being inaccurate for your particular situation.

three runners on top of a grassy rocky hill