Marathon Time Predictor Calculator

How can you predict a Marathon?

Predicting a marathon time based on a shorter race (like a 5K or 10K) is not an exact science, but it is supported by robust physiological models. The most widely accepted method is **Riegel's Formula**, developed by Peter Riegel in 1977. It suggests that a runner's speed will decline at a predictable rate as distance increases. This Marathon Predictor uses this logarithmic model to estimate your finishing potential for the 26.2-mile distance.

It is crucial to remember that a prediction is only a "potential time." For the prediction to be accurate, you must have an aerobic base built through Zone 2 training, which you can calculate using our Heart Rate Zone Tool. Without specific marathon endurance training, Riegel's formula will significantly underestimate your finish time.

The Mathematical Engine: Riegel's Formula

The Fatigue Coefficient (b)

The standard coefficient of 1.06 assumes the runner has trained balanced for the target distance. However, human physiology varies:

• 1.05 (Endurance Specialists): For runners who thrive on high-mileage weeks and typically perform better as the distance grows.
• 1.06 (Balanced): The appropriate setting for 80% of amateur runners.
• 1.08 (Speed Specialists): For runners with high fast-twitch muscle fibers who can run a fast 5K but struggle with the metabolic depth of a marathon.

Caloric Demand of a Marathon

Running a marathon requires roughly 2,600 to 3,000 calories for the average adult. Since the human body can only store about 2,000 calories of glycogen, "hitting the wall" at Mile 20 is a common physiological event. To avoid this, ensuring your Macro Ratios are high in carbohydrates during the 48 hours leading up to the race is vital.

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Frequently Asked Questions (FAQ)