Race Time Predictor
Use your known race result to predict your performance at any distance. Combines three proven formulas for accurate estimates.
Known Race Result
Hours
Minutes
Seconds
Target Distance
Predicted Time
Low confidenceAverage of 3 formulas
3h 53:06
Pace: 5:31 /km · 8:53 /mile
Riegel
3h 50:01
Cameron
3h 59:45
VO2max
3h 49:34
| Distance | Predicted Time | Pace /km | Pace /mile |
|---|---|---|---|
| 5K | 24:06 | 4:49 | 7:45 |
| 10K | 50:00 | 5:00 | 8:03 |
| Half Marathon | 1h 50:55 | 5:15 | 8:28 |
| Marathon | 3h 53:06 | 5:31 | 8:53 |
| 50K | 4h 39:30 | 5:35 | 8:60 |
About these predictions:
- Riegel: Best for similar distances (±25%)
- Cameron: More accurate for longer distances
- VO2max: Based on aerobic capacity estimation
- Predictions are estimates and actual performance depends on many factors
How to predict your race time
Race time prediction uses mathematical formulas to estimate how fast you'll run at a different distance based on a known race result. If you've run a 10K, you can predict your marathon time. The most common formula is the Riegel formula, which accounts for the fact that maintaining the same pace over longer distances becomes progressively harder due to fatigue.
Prediction formulas compared
This tool combines three proven formulas. Each has different strengths depending on the distance ratio between your known result and your target:
| Formula | Method | Best for | Accuracy |
|---|---|---|---|
| Riegel | Power law: T₂ = T₁ × (D₂/D₁)^1.06 | Similar distances (5K→10K) | Very good |
| Cameron | Polynomial decay factor | Longer jumps (10K→marathon) | Good for long distances |
| VO2max | Based on estimated VO2max | All distances, physiological | Good baseline |
Example predictions from a 10K result
Here's what typical predictions look like for a runner with a 50-minute 10K (5:00/km pace), using the average of all three formulas:
| Target distance | Predicted time | Predicted pace |
|---|---|---|
| 5 km | 23:50–24:10 | 4:46–4:50/km |
| Half-marathon | 1h49–1h53 | 5:10–5:20/km |
| Marathon | 3h50–4h00 | 5:27–5:41/km |
| Trail 50 km | 5h10–5h40 | 6:12–6:48/km |
Frequently asked questions
How accurate are race time predictions?
Predictions are most accurate when the source and target distances are relatively close (e.g. 10K to half-marathon). The further apart the distances, the more variables (endurance, fueling, training volume) affect the result. Predictions assume proper training for the target distance.
Can I predict trail times from road results?
Predictions from road to trail are less reliable due to terrain, elevation, and technical difficulty. A general rule: add 20-40% to your flat road prediction for a trail with moderate elevation. For very technical trails, the difference can be even greater.
Which formula should I trust most?
Use the average of all three as your baseline. Riegel is most trusted for close distances, Cameron better for big jumps (5K→marathon). If you have good endurance training, trust Cameron; if you're more speed-oriented, lean toward Riegel.
How recent should my reference result be?
Ideally, use a result from the last 3-6 months where you ran at full effort. Older results may not reflect your current fitness. A training time trial can also serve as reference if you don't have a recent race.