Race Time Predictor
Fill in the values and the answer updates as you type.
How the Race Time Predictor works
Uses the Riegel formula: T₂ = T₁ × (D₂ ÷ D₁)^1.06. It assumes you train well for the longer distance; marathons in particular often run slower than predicted without enough long runs. Times are shown as hours:minutes:seconds.
Inputs and results
The Race Time Predictor takes 3 inputs and gives 5 results.
What you enter
- Distance you ran — starts at 5 km. Choose from: 1 mile, 5 km, 10 km, Half marathon and Marathon.
- Finish time, minutes (min) — starts at 25.
- Finish time, seconds (sec) — starts at 0.
What you get
- Predicted 5 km
- Predicted 10 km
- Predicted half marathon
- Predicted marathon
- Your pace per km
Example: Race Time Predictor with the starting values
With distance you ran 5 km, finish time, minutes 25 min and finish time, seconds 0 sec, the calculator returns:
| Predicted 5 km | 0:25:00 |
|---|---|
| Predicted 10 km | 0:52:07 |
| Predicted half marathon | 1:55:00 |
| Predicted marathon | 3:59:47 |
| Your pace per km | 5:00 |
Change any value above and the results update straight away.
Race Time Predictor FAQ
How do I use the Race Time Predictor?
Enter distance you ran, finish time, minutes and finish time, seconds in the fields, then read predicted 5 km, predicted 10 km, predicted half marathon and predicted marathon in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Race Time Predictor calculate?
Predict 5K, 10K, half marathon, and marathon times from one result. It returns predicted 5 km, predicted 10 km, predicted half marathon and predicted marathon from the 3 values you provide.
What values does the Race Time Predictor start with?
It opens with distance you ran 5 km, finish time, minutes 25 min and finish time, seconds 0 sec so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Race Time Predictor free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Race Time Predictor for medical or health decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm medical or health decisions with a qualified professional. See the Disclaimer for more.