Carb Loading Calculator
Daily carb target for endurance carb-loading in the days before an event.
Overview
Carb loading is the deliberate practice of saturating muscle and liver glycogen stores in the days before a long endurance event. Done well, it can extend the duration that an athlete sustains race-pace effort before "hitting the wall" — the point at which depleted glycogen forces a sharp drop in intensity. A carb-loading calculator works out the daily carbohydrate target in grams so you can plan meals without guesswork.
The protocol is most relevant for events lasting longer than about 90 minutes, such as marathons, century rides, long-course triathlons, and stage races. For shorter sessions, normal mixed-carbohydrate intake is sufficient, and over-fuelling simply leads to gastrointestinal discomfort and excess water retention.
How it works
The modern recommendation, refined by exercise physiologists from the original Scandinavian "depletion-load" protocol, is to consume 8 to 12 grams of carbohydrate per kilogram of body weight per day for the one to three days before competition. The calculation is daily_carbs_g = body_weight_kg × g_per_kg, where the multiplier is chosen by event length, training status, and personal tolerance.
Each gram of stored glycogen binds roughly 3 grams of water, which is why successful loading is accompanied by a 1 to 2 kg weight gain on the scale — a feature, not a bug, since that water is released during exercise. The tool typically defaults to 10 g/kg for a marathon-class effort and provides a multi-day ramp so intake increases gradually rather than all at once.
Examples
- A 70 kg marathon runner at 10 g/kg targets 700 g of carbohydrate per day for two days pre-race — roughly 2,800 kcal from carbs alone.
- A 60 kg cyclist preparing for a six-hour gran fondo at 8 g/kg targets 480 g of carbs per day for three days.
- An 85 kg Ironman athlete at 12 g/kg the day before targets 1,020 g — usually split into many small frequent meals.
- A 75 kg half-marathoner at 6 g/kg (mild load) targets 450 g per day, suitable for an event under two hours.
FAQ
Will I gain weight from carb loading?
Yes, about 1 to 2 kg of water bound to fresh glycogen. It is shed during the race and is exactly what powers your effort.
Should I add fat and protein on top?
Keep them modest. High-fat and high-fibre foods slow gastric emptying and crowd out glycogen-replenishing carbs.
What foods work best?
Easily digested starches like rice, pasta, bread, potatoes, oats, and sports drinks. Whole-grain heavy meals can backfire on race morning.
Do I still need to fuel during the race?
Yes. Stored glycogen tops out around 500 g in trained adults — enough for roughly 90 to 120 minutes of hard work.