Race Time Predictor

The Riegel formula is generally accurate within 3-5% for well-trained runners racing between 5K and marathon. It assumes similar training and conditions. Predictions are less accurate if you haven't trained specifically for the longer distance.

Yes, approximately. A 25-minute 5K predicts about a 3:50-4:00 marathon. However, marathon performance depends heavily on long-run training, nutrition, and mental toughness that shorter races don't test.

Your body shifts from aerobic to partially anaerobic energy at faster paces. Longer races require you to run at a lower percentage of your max capacity to avoid glycogen depletion. Typically, pace slows 5-6% for each doubling of distance.