Carb Loading Calculator: Body Weight → Daily Grams

How the carb loading calculator works

Carb loading maximizes muscle glycogen stores before a long race. The evidence-based target from the sports nutrition literature is 8 to 12 grams of carbohydrate per kilogram of body weight per day, spread across meals and snacks, for 24 to 72 hours depending on race distance.

For shorter races (10 km, half marathon), a single day at 8 g/kg is enough. For a full marathon, 48 hours at 10 g/kg works for most athletes. For a full Ironman or ultra, 72 hours at 10 to 12 g/kg is the standard protocol, with the last 24 hours emphasizing low-fiber, high-glycemic foods to minimize gut issues on race morning.

A 70 kg athlete targeting 10 g/kg/day needs 700 g of carbohydrate per day. That's a lot: roughly 2,800 kcal from carbs alone, which means three main meals plus three or four snacks, all carb-heavy. Rice, pasta, potatoes, bread, fruit, and sports drinks do most of the work.

The week before the race, keep fat and fiber moderate and protein normal. You are adding carbs, not substituting them for other macros. Weight gain of 1 to 2 kg during the load is normal. It's water bound to stored glycogen, and it will disappear by kilometer 20 of the marathon.

Daily carbs (g) = body weight (kg) × target (g/kg) · Typical target: 8 g/kg (short), 10 g/kg (marathon/70.3), 10–12 g/kg (full Ironman)