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 the Running Pace & Race Time Predictor?
Running Pace & Race Time Predictor Formula
Pace = Time ÷ Distance
Predicted Time = Known Time × (Predicted Distance ÷ Known Distance)^1.06
How Is the Running Pace & Race Time Predictor Calculated?
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.
Running Pace & Race Time Predictor Example
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 the Running Pace & Race Time Predictor
Step 1
Select the race distance you completed, or enter a custom distance.
Step 2
Enter your finish time in hours, minutes, and seconds.
Step 3
Review your pace per kilometer and mile.
Step 4
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.
Common Running Pace & Race Time Predictor Scenarios
Scenario 1
Setting a realistic goal pace for an upcoming longer race based on a recent shorter one.
Scenario 2
Comparing race performances across different distances on equal footing.
Scenario 3
Planning training paces based on current fitness level.
Understanding Your Result
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.
Frequently Asked Questions
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.
Where does the Riegel formula's 1.06 exponent come from?
It was derived empirically from analyzing large sets of race results across distances, representing a typical fatigue factor for trained runners rather than a theoretical constant.
Does this calculator account for terrain or weather?
No — it assumes similar conditions between your known and predicted races. Heat, hills, and altitude will all make actual race times slower than the prediction.
What training pace should I use based on my predicted race pace?
As a general guide, easy runs are typically slower than goal race pace, tempo runs are close to it, and intervals are faster — this calculator gives a target pace, not a full training prescription.
What's the difference between pace per mile and pace per kilometer?
They're the same pace expressed in different units — this calculator shows both so you can train and race using whichever unit your watch or race markers use.
Can beginners use this calculator?
Yes, but predictions are most reliable when based on a recent race or well-paced time trial rather than a casual training run.
Why might my GPS watch predict a slightly different time than this calculator?
Different tools often use different prediction models (e.g. Riegel vs. Jack Daniels' VDOT) — slight differences between them are normal and expected.
Important Information
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