Health & Medicine · Dietetics · Sports Nutrition
Carbohydrate Loading Calculator
Calculate optimal carbohydrate loading intake (grams per day) based on body weight and exercise duration for endurance performance.
Calculator
Formula
BW_kg is body weight in kilograms. R_g/kg is the recommended carbohydrate intake per kilogram of body weight per day, ranging from 8 g/kg/day for moderate-duration events (60-90 min) up to 12 g/kg/day for ultra-endurance events (>90 min). Loading typically occurs 1-3 days before the event. Caloric contribution is computed as carbs (g) × 4 kcal/g.
Source: Burke, L.M. et al. (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29(S1), S17-S27. Also: Thomas, D.T., Erdman, K.A., & Burke, L.M. (2016). Position of the Academy of Nutrition and Dietetics. Journal of the Academy of Nutrition and Dietetics, 116(3), 501-528.
How it works
Carbohydrate loading works by temporarily increasing daily carb intake relative to body weight — typically 8–12 g per kilogram of body weight per day — for 1 to 3 days before a competition. This saturates muscle and liver glycogen stores beyond their resting baseline, providing a larger fuel reserve during prolonged exercise.
The target dose depends on event duration: moderate endurance events (60–90 minutes) call for approximately 8 g/kg/day, long endurance events (90–180 minutes) benefit from 10 g/kg/day, and ultra-endurance events lasting more than 3 hours warrant the full 12 g/kg/day protocol. Because carbohydrates provide 4 kcal per gram, these targets significantly elevate daily caloric intake, which is intentional — glycogen storage also binds roughly 3 g of water per gram of glycogen.
Athletes should spread their carbohydrate intake across 5–6 meals and snacks to aid digestion and absorption. Low-fibre, easily digestible sources such as white rice, pasta, bread, sports drinks, and bananas are preferred to minimise gastrointestinal discomfort on race day.
Worked example
Example: A 70 kg marathon runner preparing for a race longer than 90 minutes wants to carb load for 2 days.
Step 1 — Identify rate: Event duration is 90–180 minutes → rate = 10 g/kg/day.
Step 2 — Daily target: 70 kg × 10 g/kg = 700 g/day.
Step 3 — Caloric contribution: 700 g × 4 kcal/g = 2,800 kcal/day from carbohydrates alone.
Step 4 — Total loading period: 700 g/day × 2 days = 1,400 g total carbohydrates over the loading window.
Step 5 — Per meal estimate: Spread over 5 meals → 700 ÷ 5 = 140 g per meal, equivalent to roughly 2–3 cups of cooked pasta or rice per meal.
Step 6 — Increase check: If the athlete currently eats 300 g/day, the required increase is 700 − 300 = 400 g/day above normal.
Limitations & notes
Carbohydrate loading is most beneficial for continuous exercise lasting 90 minutes or longer; for shorter or stop-start sports it offers minimal advantage. Individual glycogen storage capacity varies and is influenced by training status, sex, and muscle mass. Athletes with type 1 or type 2 diabetes must consult a physician and registered dietitian before attempting a loading protocol, as large carbohydrate surges can destabilise blood glucose control. The protocol may cause temporary weight gain of 1–2 kg due to water retention alongside glycogen; athletes should account for this in weight-category sports. This calculator does not account for total daily energy expenditure, protein or fat targets, or training taper adjustments — a full nutrition plan from a sports dietitian is recommended for elite competition preparation.
Frequently asked questions
How many days before a race should I start carbohydrate loading?
Most research supports a 1–3 day loading period. A 2-day protocol is common for marathon runners and triathletes: it is long enough to meaningfully top up glycogen stores while short enough to avoid excessive gastrointestinal discomfort or weight gain before the event. Starting more than 3 days out offers little additional benefit for most athletes.
Should I still train during carbohydrate loading?
Yes, but with reduced volume. Most athletes taper training intensity and duration in the 1–3 days before an event anyway, which complements the carb-loading protocol. Light exercise (20–30 minutes at easy pace) can help the body direct extra glucose into muscle glycogen without depleting the stores being built up.
Will carbohydrate loading cause weight gain?
Temporarily, yes. Each gram of glycogen stored in muscle binds approximately 3 grams of water, so maximising glycogen stores typically adds 1–2 kg of body weight. This weight is largely water and is not detrimental to performance; in fact, the additional stored water can help with hydration during prolonged exercise. The weight disappears quickly after the event as glycogen is burned.
What are the best foods for carbohydrate loading?
Low-fibre, easily digestible carbohydrate sources are preferred to reduce the risk of gastrointestinal problems on race day. Good choices include white rice, white pasta, white bread, bagels, sports drinks, energy gels, bananas, potatoes (without skin), and fruit juice. High-fibre foods like bran cereals and legumes should be minimised during the loading phase.
Does carbohydrate loading work the same for women as for men?
Research (Tarnopolsky et al., 2001) suggests women may have a slightly lower glycogen storage response to a standard carb-loading protocol compared to men when the protocol is not combined with a prior depletion phase. Some evidence indicates women may need to increase total caloric intake — not just carbohydrate proportion — to achieve comparable glycogen super-compensation. Female athletes should work with a sports dietitian to tailor the protocol to their individual needs.
Is there a carbohydrate depletion phase before loading?
Older 'classic' carbohydrate loading protocols (Bergström et al., 1967) included a 3-day glycogen depletion phase (high-intensity exercise plus a very low-carb diet) followed by 3 days of high-carb intake. Modern research (Sherman et al., 1981; Burke et al., 2011) shows that well-trained athletes can achieve comparable glycogen super-compensation with just a 1–3 day high-carbohydrate intake combined with a training taper, without the uncomfortable depletion phase. The calculator uses this modern protocol.
Last updated: 2025-01-30 · Formula verified against primary sources.