Race Time Predictor
Use a known race result to estimate finish time and target pace for another distance.
Last updated: May 30, 2026
Predicted time
52:07
Target pace
08:23 / mi
Uses the Riegel-style endurance formula with exponent 1.06. Predictions are most useful between similar road race distances and conditions.
Formula
Predicted time = known time x (target distance / known distance)^1.06.
Best Use
Estimating similar road race performances when fitness, terrain, weather, and pacing are reasonably comparable.
Limitations
Predictions get weaker when the target distance is much longer or shorter than the known race, or when terrain, heat, altitude, fueling, and endurance training differ.
Example
A 25:00 5K predicts roughly 52:07 for 10K with the 1.06 endurance exponent.
How to Use It
- Enter a recent race distance and finish time.
- Enter the target race distance.
- Use the predicted time as a planning range, then adjust for terrain, weather, training, and race-day constraints.
Common Mistakes
- Predicting a marathon from a short race without considering endurance preparation.
- Using a workout effort instead of a race or time trial.
- Ignoring course profile, heat, altitude, and fueling differences.
Useful For
- Estimate 10K potential from a recent 5K.
- Choose half-marathon pace from a recent 10K.
- Check whether a goal marathon time is plausible from shorter-distance fitness.
How accurate is a race time predictor?
It is a planning estimate. It works best for similar road race distances and conditions, not for trail races, extreme weather, or distances that require very different endurance preparation.
What recent race should I use?
Use a recent all-out race or time trial on comparable terrain. A stale result or workout effort will usually make the prediction less useful.
Can this predict a marathon from a 5K?
It can produce an estimate, but the uncertainty is high because marathon performance depends heavily on endurance, fueling, pacing, and long-run preparation.