Race Time Predictor
Use your recent race results to predict your potential performance at other distances.
Recent Performance
Predicted Finish Time
Enter your recent race details to see predictions
About the Prediction Formula
Predictions use Riegel's formula: T₂ = T₁ × (D₂ / D₁)^1.06 — where T₁ is your known time, D₁ your known distance, and D₂ the target distance. The exponent 1.06 accounts for the physiological cost of running longer distances. Results are estimates; actual performance depends on training, conditions, and race day factors.
Frequently Asked Questions
The Riegel formula is widely used and generally provides reasonably accurate predictions for most runners. However, individual variations in physiology, training, and race conditions can affect actual performance.
Yes, though predictions are more accurate between closer distances. A 5K-to-marathon prediction gives a reasonable estimate but may be optimistic if you haven't done long-distance training. For best accuracy, use a 10K or half marathon result to predict marathon time.
The formula is a general model and may not perfectly fit every runner, especially those with unique training backgrounds or physiological characteristics. It's best used as a guideline rather than an absolute prediction.
Yes, you can use your half marathon time to predict your finish time for other distances. The predictions will be more accurate for distances close to the half marathon (like 10K or marathon) than for very short distances (like 5K).
The predicted times are estimates based on your recent performance. They can help you set realistic goals and plan your training, but remember that actual race performance can be influenced by many factors such as weather, course difficulty, and your condition on race day.
Yes, you can use the predicted times to set a goal for your upcoming race.
Different calculators may use different exponents or formulas. This calculator uses the standard Riegel exponent of 1.06. Some advanced calculators adjust for age, training volume, or terrain. The Riegel formula assumes equivalent fitness and training for each distance.