Carbohydrate loading means eating extra carbohydrate for a few days before a long race so your muscles store as much glycogen as possible. Glycogen is the fuel your body burns first during hard endurance exercise, and when it runs low you slow down sharply, no matter how fit you are. That heavy, empty feeling in the last miles of a marathon is often glycogen depletion rather than a lack of fitness. Loading properly gives you a bigger fuel tank on race day, and this free calculator works out exactly how many grams you need.
The calculator uses your body weight and a grams-per-kilogram target chosen for your event. A 10K race needs only a modest increase, around 7 grams per kilogram of body weight per day, while a half marathon sits near 9 grams. A marathon, where glycogen depletion is a real risk, calls for roughly 10 to 12 grams per kilogram per day for two to three days before the race. Pick your event, enter your weight, and the tool gives your daily total, the energy it contains, and a simple per-meal split across four meals.
Here is a worked example. A 70-kilogram runner preparing for a marathon at 11 grams per kilogram needs 770 grams of carbohydrate per day. Because each gram of carbohydrate provides about 4 kilocalories, that is roughly 3,080 kilocalories from carbohydrate alone, before protein and fat are counted. Split across four meals, that is about 193 grams per meal, which is a large amount of food. Planning it in advance matters, because eating that much by accident on race week is almost impossible.
Choose carbohydrate-rich foods that you already know and tolerate well, and do not experiment with new foods in race week. Rice, pasta, bread, oats, potatoes, and fruit juice are all practical choices, and they are easy to eat in large amounts. Spread the carbohydrate across the whole day rather than eating one enormous meal, and keep fibre and fat moderate so your stomach stays comfortable. Drink normally alongside the food, since glycogen is stored together with water in the muscle.
Carbohydrate loading only helps for events long enough to drain glycogen, which usually means efforts lasting longer than about 90 minutes. For a 5K or a short gym session, a normal balanced diet is plenty, and extra loading just adds body weight. For a marathon or a long triathlon, however, the difference between a full tank and a half-empty one can be the difference between a strong finish and a long walk. Match the loading to the event, not to your enthusiasm.
Timing matters as much as the total. Most runners load for two to three days before the race, then eat a familiar carbohydrate-rich meal the evening before and a smaller one a few hours before the start. Do not load for a full week, and do not keep eating huge amounts on race morning, when a full stomach will slow you down. Your last big meal should be finished well before the start, with only small, familiar snacks after that if you need them.
Expect your weight to rise by one or two kilograms during loading, and do not panic about it. Each gram of stored glycogen holds about three grams of water, so a heavier scale reading means the loading is working, not that you have gained fat. That stored water is useful during the race, and the weight will come off again as you burn the glycogen. Judge the plan by how you feel in the race, not by the scale in race week.
A common mistake is loading with sugary drinks and sweets alone, which can leave you feeling sick and under-fuelled. Another is cutting protein and vegetables to zero, which makes meals unbalanced and hard to digest. Keep some protein at each meal, keep vegetables in smaller portions than usual, and keep the total food volume manageable. If you feel bloated, swap some bulky foods for juices, white bread, or rice, which pack more carbohydrate into less volume.
This calculator gives an educational nutrition estimate, not medical advice. It does not diagnose or treat any condition, and it cannot replace a sports dietitian, especially if you have diabetes, a digestive disorder, or any condition that affects how you eat. If a loading plan makes you feel unwell, stop and seek professional advice. Use the numbers as a starting point, adjust them to your own experience, and keep notes on what worked for your next race.
Build your race-week food plan around the calculator result, then shop and cook ahead so race week stays calm. Write down each meal, check the carbohydrate totals the day before, and keep a few backup options ready in case your appetite drops. Good fuelling rarely makes headlines, but it quietly decides how strong you feel in the final miles. Run the numbers now, eat with a plan, and arrive at the start line with a full tank.
Calculadora de Carga de Carbohidratos – Herramienta Gratis de Entrenamiento
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