Predict your potential finish times for various distances based on a recent race result. We analyze your potential using the globally recognized Riegel's Formula.
Race Time Predictor - 5K, 10K, Half & Marathon
Predict your potential finish times for various distances based on a recent race result. We analyze your potential using the globally recognized Riegel's Formula.
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Enter your data
Enter a recent race distance and finish time
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Calculate
Click predict to calculate times for other distances
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Review results
View predicted finish times for 5K, 10K, half marathon, and marathon
Race Time Predictor
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Predict your race performance based on a recent result (Riegel's Formula).
It's a tool that calculates expected finish times for other distances based on a recent race result.
Race predictions based on the Riegel formula are most accurate when predicting between similar distances (e.g., 10K to half marathon). Accuracy decreases for larger distance jumps. Predictions assume similar training and race-day conditions.
The Riegel formula predicts race times using: T2 = T1 × (D2/D1)^1.06, where T1 is your known time, D1 is the known distance, and D2 is the target distance. The exponent 1.06 accounts for the fatigue factor over longer distances.
Yes, but with caveats. A 5K-to-marathon prediction assumes you have adequate long-distance training. A 25-minute 5K runner might predict around 3:55 for a marathon, but without proper marathon-specific training, the actual time could be significantly slower.
The standard exponent is 1.06, representing the rate at which runners slow down over longer distances. A higher value (e.g., 1.08) suits less-trained runners, while elite endurance athletes may use 1.04-1.05.
Common reasons: insufficient long-run training, poor pacing strategy (starting too fast), inadequate nutrition during the race, hot weather, or hilly course. The formula assumes optimal conditions and proper training for the target distance.
Ideally within the last 6-8 weeks and run at maximum effort. Older results may not reflect your current fitness. Training races or time trials work too, as long as they were genuine all-out efforts.
Less so. The Riegel formula is most accurate between 5K and marathon distances. For ultras (50K+), additional factors like nutrition strategy, sleep deprivation, and terrain play a much larger role that the formula doesn't account for.
Race prediction assumes optimal conditions: flat course, good weather, proper pacing, and adequate training. Hills, heat, wind, or insufficient long runs can all cause actual times to exceed predictions. The models also assume equal training for both distances.
The Riegel formula becomes less accurate beyond marathon distance. For ultras (50K+), fatigue factors increase non-linearly. The formula may underestimate ultra times by 5-15%. Specialized ultra prediction models account for elevation gain, aid station time, and sleep deprivation.
Treadmill times can be used as input, but outdoor races involve wind resistance, terrain changes, and temperature variation. As a rule of thumb, add 10-15 seconds per km to your treadmill pace for a real-world equivalent. Set the treadmill to 1% incline to better simulate outdoor conditions.