Race Time Predictor
Forecast your potential across any distance
What is the Race Predictor?
The Race Predictor is a powerful tool that estimates your potential finish times for various race distances based on a recent race result. It uses the renowned Riegel formula to account for how runners naturally slow down as distance increases, providing realistic predictions for 5K, 10K, Half Marathon, Marathon, and Mile distances.
How to Use the Race Predictor
The formula is based on Pete Riegel's research: T2 = T1 × (D2 / D1)^1.06, where T1 is your known time, D1 is the distance you ran, D2 is your target distance, and T2 is your predicted time.
If you ran a 5K in 25:00 (25 minutes):
Marathon Time = 25 × (42.195 / 5)^1.06 = 25 × 8.44^1.06 ≈ 234 minutes
Your predicted marathon time is approximately 3:54:00.
Understanding Your Predictions
The Riegel formula has been validated by thousands of runners over decades. The exponent 1.06 accounts for the physiological reality that pace decreases as distance increases due to energy system fatigue and biomechanical efficiency loss.
Important Considerations
Prediction is not a guarantee. While the math holds up, physiology differs. A fast 5K runner may lack the endurance base for a marathon. Treat these predictions as "potential" assuming you train specifically for the target distance. Factors like terrain, weather, training volume, and race experience all impact your actual performance.
Training Zones and Related Tools
Once you have your predicted times, use them to establish proper training paces. Check out our Training Pace Calculator to determine your easy, tempo, and interval paces based on your goal race time.
Frequently Asked Questions
How does the race predictor work?
It uses Pete Riegel's famous formula: T2 = T1 * (D2 / D1)^1.06. This formula assumes that a runner slows down slightly as distance increases.
Is this accurate for beginners?
The formula assumes you have trained appropriately for the target distance. It predicts potential. A 5K time can predict a Marathon time, but only if you have done the long runs.
What is the Riegel formula?
The Riegel formula (T2 = T1 × (D2 / D1)^1.06) was developed by Pete Riegel to predict race times at different distances. The exponent 1.06 accounts for the fact that runners slow down as distance increases.
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