Plans, paces & PBs Choose the Recent Race
Select the distance of your current result or enter a custom accurately measured distance.
Race Time Predictor
Running Race Time Predictor
Enter a recent race result to estimate equivalent finish times for one mile, 5K, 10K, half marathon and marathon.
How to use it
Use the strongest recent evidence.
A current result from a nearby distance normally gives a more defensible prediction than a distant lifetime personal best.
Enter the Finish Time
Use the complete hours, minutes and seconds from a race or hard time trial.
Check the Training Assumption
Use the estimates as reference points, then account for the endurance and preparation required by the target distance.
Worked example
Predictions from a 20-minute 5K.
The formula progressively slows the equivalent pace as distance increases.
| Distance | Predicted time | How to treat it |
|---|---|---|
| 1 mile | 6:01 | A nearby speed estimate |
| 5K | 20:00 | The entered result |
| 10K | 41:42 | Usually achievable with suitable 10K preparation |
| Half marathon | 1:32:00 | Requires developed aerobic endurance |
| Marathon | 3:11:49 | Highly dependent on mileage, long runs and fuelling |
How the prediction is calculated
Predicted timeT₁ × (D₂ ÷ D₁)1.06
T₁ and D₁Your known time and distance
D₂The distance being predicted
The 1.06 exponent allows average pace to slow as distance increases instead of assuming you can hold the same pace indefinitely.
Speed does not automatically create endurance.
A fast 5K can predict marathon potential, but it cannot prove marathon readiness. Training volume, long runs, fuelling, weather and course profile become increasingly important over longer distances.
Predictions between nearby distances are generally more useful than large jumps.
Use the prediction
Choose a realistic next training target.
Frequently Asked Questions
Race prediction questions
How does a race time predictor work?
The predictor uses a recent race result and the Riegel formula to estimate equivalent performances at other distances. It allows for pace to slow as the target distance increases.
How accurate is the Riegel race prediction formula?
It is a useful starting estimate, not a guarantee. Predictions are generally more useful between nearby distances and when your training supports the target event.
Why can a 5K result overestimate my marathon time?
A strong 5K demonstrates speed but not necessarily the endurance, fuelling experience or long-run preparation needed for a marathon. Longer-distance estimates assume appropriate training.
Which race result should I enter?
Use a recent race or hard time trial completed in representative conditions. Choose the result that best reflects your current fitness and is reasonably close to the distance you want to predict.
Can I use a training run instead of a race?
You can use a hard, accurately measured time trial, but an ordinary training run will usually produce conservative predictions because it was not completed at race effort.
Should I use the predicted time as my next race target?
Treat it as a sensible reference point. Check the distance-specific training demands, your recent volume and the conditions before adopting it as a goal.