Race Time Predictor
Estimate your potential finishing time for another race distance using a previous race result. Compare your predicted pace and average speed.
Enter your race details
Choose your previous race, enter your finishing time, and select the race you want to predict.
Estimated Race Result
Race predictions are mathematical estimates and may differ from actual finishing times.
Your result depends on your current fitness, endurance, training, course conditions, weather and pacing. Predictions over larger distance changes are particularly uncertain.
How does the Race Time Predictor work?
Our calculator uses the Riegel formula, a mathematical model that estimates performance at one race distance using a finishing time from another distance.
The formula accounts for the fact that runners generally cannot maintain the same average speed indefinitely as race distance increases.
In this formula, T1 represents your previous finishing time, D1 is your previous race distance, D2 is your target race distance, and T2 is the predicted finishing time.
Example: Predicting a 10K from a 5K
Imagine you have completed a 5K race in 25 minutes and want to estimate your 10K time.
The calculator starts with 25 minutes and adjusts that time using the ratio between 10 kilometres and 5 kilometres.
The estimated 10K finish is approximately 52 minutes and 7 seconds. That corresponds to an average pace of roughly 5:13 min/km.
Which previous race should you use?
A recent, accurately timed race completed at a representative effort is generally more useful than an old performance or an easy training run.
Predictions are usually more meaningful when the two race distances are reasonably similar and you have trained appropriately for the target event.
Why might the prediction be inaccurate?
A mathematical formula cannot account for every difference between runners. Marathon results, for example, depend heavily on endurance preparation, fueling, pacing and race conditions.
Use your prediction as a starting point for planning rather than as a guaranteed finish time or a requirement to run at a particular pace.
Frequently Asked Questions
Can I predict my marathon time from a 5K?
Yes, but this is a rough estimate. A marathon places very different demands on endurance, preparation, pacing and fueling. A fast 5K alone does not mean you are ready to complete a marathon at the predicted pace.
Can I use a 10K result to predict a 5K?
Yes. The formula can estimate shorter races as well as longer ones. Choose 10K as your previous race, enter your time, and select 5K as the target distance.
Which previous race should I enter?
Use a recent, accurately measured race completed at a strong, representative effort. Results from a distance close to your target race tend to provide a more useful starting point than a much shorter or older performance.
Why is my predicted 10K time more than twice my 5K time?
The Riegel formula uses an exponent of 1.06 to account for the usual reduction in sustainable average speed as race distance increases. Two times your 5K distance therefore produces a predicted time slightly longer than twice your 5K finish.
What happens if I select the same race distance twice?
The prediction equals your previous finishing time, because the distance ratio is one. Select a different target race to compare your performance across distances.
Is the predicted finishing time guaranteed?
No. It is a mathematical estimate, not a personal training assessment. Fitness, endurance, race conditions, terrain, weather and pacing can all affect your actual result.