Race Time Predictor
Predict an equivalent race time with the Riegel equation and warn when extrapolation distances are far apart.
Enter or adjust the values above, then calculate.
Race Time Predictor: predict 5K, 10K, Half & Marathon Time
Predict an equivalent race time with the Riegel equation and warn when extrapolation distances are far apart.
Inputs this tool uses
- Known race distance
- Known finish time
- Target distance
What you get
Riegel race-time projection.
How to use the Race Time Predictor
- Enter known race distance, known finish time, target distance.
- Select any method, activity level or option shown on this page, then choose Calculate.
- Read the main result together with the supporting values, method, assumptions and limitations below before using the estimate.
How this calculation works
Race prediction uses the Riegel power-law projection and warns when distances are far apart.
Example calculation
The sample values loaded into the calculator produce 0h 52m. This example exists to show how the output is structured; replace the sample values with your own inputs for your calculation.
Assumptions and limitations
- Energy, fitness and heart-rate outputs are estimates and vary by individual and device.
- Stop exercise and seek appropriate care if you have concerning symptoms; this tool does not provide medical clearance.
Sources and review status
Source set last verified 2026-09-25. No clinician review is claimed unless a real named reviewer is displayed.
Questions people ask about Race Time Predictor
How accurate is a race-time predictor?
The Riegel projection assumes performance scales predictably with distance. It is most useful when the known and target distances are reasonably close; marathon endurance and conditions can cause larger errors.
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