XACT Marathon Calculator

Science-backed fuel plan for your 42.2 km

What is your body weight?

Used to calculate your energy expenditure and glycogen stores.

What is your target finish time?

hrs

min

Your pace determines intensity and fuel substrate utilization.

Gut tolerance

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

During

After

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.