Race Predictor Calculator

Race predictions are estimates based on your current fitness level using mathematical models like the Riegel formula. Accuracy varies based on several factors: your training specificity (a 5K specialist may underperform at marathon distance), terrain differences, weather conditions, and pacing strategy. Predictions are typically most accurate for distances close to your input race (e.g., predicting 10K from 5K is more accurate than predicting marathon from 5K).

The Riegel formula is a mathematical model used to predict race times across different distances. It states that T2 = T1 × (D2/D1)^1.06, where T1 and T2 are times, and D1 and D2 are distances. The exponent 1.06 accounts for the fact that runners slow down slightly at longer distances due to fatigue accumulation. This formula has been validated across thousands of race performances.

Yes, but with less accuracy than predicting closer distances. A 5K primarily tests speed and VO2max, while a marathon tests endurance and glycogen management. If you're a 5K specialist with limited long-distance training, the prediction will likely be optimistic. For best results, use your longest recent race to predict marathon times, and ensure you have adequate endurance training.

Training paces are specific intensity zones for different workout types. Easy pace builds aerobic base without excessive fatigue. Tempo pace (threshold pace) improves lactate clearance and race-pace comfort. Interval pace develops VO2max and running economy. Training at appropriate paces maximizes adaptations while managing recovery, leading to better race performances.

Use predictions as goal targets rather than guarantees. They represent your current potential assuming proper training, favorable conditions, and good pacing. When planning for a race, consider: 1) Have you trained specifically for that distance? 2) Is the course similar to your recent race? 3) What are expected weather conditions? Adjust your goal slightly based on these factors.

As race distance increases, pace per kilometer decreases because maintaining high intensity becomes progressively harder. This is due to glycogen depletion, muscle fatigue, biomechanical inefficiency from fatigue, and mental factors. The Riegel exponent of 1.06 accounts for this slowdown. Elite runners have a smaller slowdown (exponent closer to 1.05) while beginners may have larger slowdowns (1.07-1.08).

Update predictions after each race or time trial, or every 4-6 weeks during focused training. Your fitness changes with training, so predictions from months ago may not reflect current ability. If you're focusing on a specific distance (like marathon training), your predictions for that distance will improve more than predictions based on the formula alone due to training specificity.