Race time predictor for 5K, 10K and half marathon
Enter a recent race or all-out time trial between one mile and a half marathon. The predictor estimates your time at the other distances using the Riegel formula, in which time grows with distance raised to the power 1.06.
Race time predictor
Enter a distance and time to see estimates.
How to use it
The same formula sets the optional pace ranges in our training plans, so a prediction here is consistent with a plan built from the same result.
- Choose the distance of your recent race.
- Enter your finish time.
- Read the estimates, paying attention to the reliability note on each row.
Limits you should know
- A prediction assumes you train for the longer distance and race in similar conditions. Without that training, your real time can be slower than the estimate.
- Estimates get rougher as the target moves further from your result. We label each row close, moderate or rough by distance ratio. That label is our own rule of thumb, not a measured accuracy.
- Use a race or hard time trial run in the last several weeks. An easy run or an old result will mislead.
Questions about this tool
How accurate is the Riegel formula?
It is a rule of thumb, not a precise model, and we have not measured its accuracy. We label each row by how far the target is from your result, which is our own rule of thumb about how much to trust it.
Why might my half marathon come out slower than predicted?
The formula starts from a shorter result and does not know your training. If your weekly mileage and long runs are low for the distance, your real time can be slower. This is general advice, not output from the engine.
Can I predict a marathon?
Not here. Marathon plans are not available yet, and the predictor accepts only races between 1 mile and a half marathon.
From a number to a plan
Training plans use these same calculations. Six questions give you a week-by-week calendar from the miles you run now.
More tools: Pace calculator, Training pace calculator, Race readiness checker.