Carb loading calculator
Enter your body weight and how long your event will take. You get a daily carbohydrate target for the last two days and the size of your last meal before the start.
Your plan
Enter your body weight and how long your event will take. You get a daily carbohydrate target for the last two days and the size of your last meal before the start.
What is carb loading?
Carb loading means filling your muscles with as much stored carbohydrate (glycogen) as possible before an event. You eat more carbohydrate than usual for the last day or two, while you train less.
When does it make sense?
Mainly for events longer than 90 minutes. At a hard effort, the muscles can be largely emptied after about an hour, and your gut can only take in so much on the move. A full store helps you avoid running dry and saves energy for the decisive moments. For a 90 minute event you do not need aggressive loading. Beyond three to four hours a full store matters most.
How it works in practice
Ideally 24 to 48 hours before the start. The guideline is 6 to 12 g of carbohydrate per kg per day for 36 to 48 hours, together with a lower training volume, while your total energy intake stays in balance. Do not let it become a feast on the last night: spread it over several meals.
Fiber and your stomach
Fiber and some other carbohydrates (FODMAPs) draw water into the gut and ferment, which can cause gas and pressure during the race. A sensible ceiling is about 10 g of fiber per 1,000 kcal. If your stomach is sensitive, a short low FODMAP period of 2 to 3 days can help, ideally with a sports dietitian. Going below 6 g per 1,000 kcal is only for long events, used rarely, and with a coach.
Breakfast and the last meal
Eat a carbohydrate rich meal 1 to 4 hours before the start: about 1 g per kg when it is one hour before, up to 4 g per kg when you have four hours. Keep it low in fiber and fat. If the start is late in the day, keep eating easily digestible carbohydrates, such as white rice, white bread with jam, or a carbohydrate drink.
General information for healthy adults, not medical advice. If you have diabetes, a gut condition, an eating disorder, or take medication, talk to your doctor or a sports dietitian first.
Common questions
How many days before a marathon should I carb load?
Mostly the last 36 to 48 hours. You do not need a week. Reduce training at the same time.
How many grams of carbs per kg for carb loading?
The guideline is 6 to 12 g per kg per day. The calculator picks a range that fits your event length.
Do I need to carb load for a 10K or a 90 minute race?
No. Normal, well fueled days are enough for events under 90 minutes.
Will carb loading make me gain weight?
Stored carbohydrate holds water, so a small rise on the scale before the start is normal and works in your favor.
Want this planned around your own week?
The 2fuel app turns every training session into kcal, carbs per hour and protein, then into meals. With an AI coach or a sports dietitian. In beta now.