Running Pace & Race Time Predictor
Find your pace and predict finish times for other race distances.
Race Distance
Finish Time
hr
min
sec
Pace per km
5:00/km
Pace per mile
8:03/mi
Predicted finish times
What is it?
This calculator finds your running pace from a race distance and finish time, then uses the Riegel formula to predict your finish time for other common race distances based on that performance.
Formula
Pace = Time ÷ Distance
Predicted Time = Known Time × (Predicted Distance ÷ Known Distance)^1.06
Formula Explanation
Pace is simply your total time divided by distance covered. The Riegel formula predicts race times for other distances using a 1.06 exponent, which accounts for the fact that pace naturally slows over longer distances due to fatigue — it's not a simple linear scale-up of your shorter-distance pace.
Example Calculation
A 25-minute 5K predicts a 10K finish time of roughly 52 minutes (not simply double, thanks to the 1.06 exponent), and a half marathon of about 1:55:00.
How to Use
- Select the race distance you completed, or enter a custom distance.
- Enter your finish time in hours, minutes, and seconds.
- Review your pace per kilometer and mile.
- Check predicted finish times for other common race distances.
Benefits
- Uses the Riegel formula's fatigue-adjusted exponent instead of a naive linear pace scale-up.
- Shows pace in both per-kilometer and per-mile units.
- Predicts times across all major race distances from a single known performance.
Use Cases
- Setting a realistic goal pace for an upcoming longer race based on a recent shorter one.
- Comparing race performances across different distances on equal footing.
- Planning training paces based on current fitness level.
What Your Result Means
Predicted times assume similar training and conditions between races — they represent a reasonable target if you train appropriately for the new distance, not a guarantee. Endurance-specific training becomes increasingly important as predicted distances get longer, since the formula doesn't account for how well-trained you are for endurance versus speed.
Tips
- Predictions are most reliable when the known and target distances aren't too far apart — predicting a marathon from a 1-mile time is far less reliable than from a half marathon.
- Use a recent, well-rested race performance for the most accurate prediction — a hard training run rarely reflects true race pace.
- Endurance training becomes increasingly important for accurate predictions at longer distances.
Common Mistakes
- Assuming pace stays constant across distances — actual race pace naturally slows as distance increases, which the Riegel exponent accounts for.
- Using a poor or unrepresentative performance (e.g. a run in extreme heat) as the basis for prediction.
- Treating predicted times as guaranteed rather than as a training target requiring appropriate endurance preparation.
FAQs
How accurate is the Riegel formula?
It's a widely used and reasonably accurate predictor for well-trained runners over similar terrain and conditions, though individual factors like endurance training and race-day conditions can cause real results to vary.
Can I predict a marathon time from a 5K?
Yes, but predictions become less reliable the larger the gap between known and target distances — a half marathon or 10K time predicts a marathon more reliably than a 5K does.
Why isn't my 10K time just double my 5K time?
Because pace naturally slows over longer distances due to fatigue — the Riegel formula's 1.06 exponent captures this, which is why predicted times are always somewhat slower than a simple linear scale-up.
Predictions assume comparable training, terrain, and conditions between races — actual results depend on your specific endurance preparation for the target distance.
Last updated: July 26, 2026