Free Tool · Race Nutrition

Carb Loading Calculator

How many carbs do you need before your marathon? Enter your weight and race distance to get personalised daily carbohydrate targets and a meal-by-meal plan for your loading days.

Your Details
Carbs Per Day
700g
10g × 70kg
Calories from Carbs
2800
kcal/day
Total over 2 days
1400g
total carbs
Suggested Meal Distribution (700g/day)
Breakfast175g carbs
e.g. Oats with banana, orange juice, wholegrain toast with jam
Morning Snack105g carbs
e.g. Bagel with honey, sports drink, dried fruit
Lunch210g carbs
e.g. Pasta with tomato sauce (low fat), white bread roll, banana
Afternoon Snack105g carbs
e.g. Rice cakes, sports gel, orange juice
Dinner105g carbs
e.g. White rice with chicken breast, white bread, sports drink
⚠️ Keep fat intake low during loading days — fat slows gastric emptying and reduces carb absorption. Keep total fat under 60g/day and avoid anything greasy, fried, or high-fibre.

What Is Carb Loading?

Carbohydrate loading (glycogen supercompensation) is the practice of eating a high-carbohydrate diet in the 1–3 days before an endurance race. The goal is to maximise the amount of glycogen stored in your muscles and liver — your primary fuel source during race-pace running.

A typical runner stores roughly 400–600g of glycogen when fully loaded. This provides approximately 1,600–2,400 calories of quickly accessible fuel — enough for 90–120 minutes of race-pace running. For a marathon, which takes most recreational runners 3–5 hours, this means you'll need to top up with mid-race nutrition even with optimal loading.

How Much to Eat: The Science

Sports nutrition research recommends 8–12g of carbohydrate per kg of body weight per day during the loading phase:

For a 70 kg runner, a full marathon loading protocol means consuming 700g of carbohydrate per day — approximately 2,800 calories from carbs alone. This requires deliberate meal planning and intentionally reducing fat and protein intake to make room for carbohydrates.

What to Eat (and Avoid) During Loading

Best carb loading foods: white rice, white pasta, white bread, bagels, oats, potatoes (without skin), sports drinks, bananas, orange juice, honey, rice cakes, breakfast cereals (low-fibre).

Avoid during loading days:

Race Morning Breakfast

The morning of the race, eat a high-carbohydrate, low-fat, low-fibre breakfast 2–4 hours before the start:

If you're running early and can't eat 2–4 hours beforehand, a small easily digestible snack 60–90 minutes before (banana, white toast, sports gel) is better than nothing.

Mid-Race Fuelling

Even with optimal carb loading, you'll need mid-race nutrition for a marathon. Take a gel or sports drink every 45 minutes from the 15 km mark onwards. Missing fuelling windows is the #1 cause of the marathon wall — your loaded glycogen stores don't last the full 42 km at race pace.

Frequently Asked Questions

Carb loading (glycogen supercompensation) is the practice of consuming high amounts of carbohydrate in the days before a long endurance race to maximise muscle and liver glycogen stores. Your body stores roughly 500–600g of glycogen (about 2,000–2,400 calories of carbohydrate). Fully loaded stores can fuel approximately 90–120 minutes of race-pace running — critical for avoiding the marathon wall at km 32.
For a marathon: start 2–3 days before race day. For a half marathon: 1–2 days is usually sufficient. The research is clear that longer loading periods (7 days) don't produce significantly better results than 2–3 day protocols, and they come with more gastrointestinal risk. Keep carb loading to a maximum of 3 days for practical and gut health reasons.
Choose easily digestible, low-fibre carbohydrate sources: white rice, white pasta, white bread, bagels, oats, bananas, fruit juice, sports drinks, and honey. Avoid high-fibre foods (wholegrain bread, beans, lentils), high-fat foods, and anything your gut isn't used to. Race week is not the time to try new foods.
Yes — expect 1–3 kg of temporary weight gain during carb loading. Every gram of glycogen is stored with approximately 3 grams of water, so fully loaded glycogen stores carry extra water weight. This is normal and not fat gain. The weight disappears as you burn glycogen during the race and is a sign that loading was successful.
Yes. The 2–3 days before a marathon should be very easy or rest days. Reduced training and increased carbohydrate intake is the combination that maximises glycogen supercompensation. Heavy training while carb loading is counterproductive — you'll burn glycogen faster than you can store it.
Probably not. A 10K race typically lasts 40–70 minutes for recreational runners — well within the 90–120 minute window where glycogen depletion becomes a performance limiting factor. A slightly higher carbohydrate dinner the night before and a light carbohydrate breakfast on race morning is sufficient for most 10K runners.

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