XACT Race Calculator

Science-backed fuel plan for your race

21.1 kmHalf Marathon
42.2 kmMarathon
kg
Used to calculate your energy expenditure and glycogen stores.
hrs
min
Your pace determines intensity and fuel substrate utilization.
Your Carbohydrate Target
55g/hr
Total: 250g for your marathon
3,200
Total kcal burned
2,025
mg sodium target
500
mL/hr hydration

Before

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During

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After

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Your Race Fuel Timeline

How we calculated this: Energy expenditure via the Léger equation for running economy. Glycogen stores estimated at 12.5 g/kg muscle mass. Carbohydrate target replaces 50–60% of oxidized carbs. Sodium at 450 mg/hr per ACSM guidelines.