Pre-race nutrition
Carb loading calculator.
Grams of carbohydrate per day for one to three days before a long event, from your body mass, using the range in the ISSN nutrient timing position stand.
Inputs
Daily carbohydrate
Enter your body mass.
How many carbs should I eat to carb load?
The ISSN position stand on nutrient timing describes carbohydrate loading in the days before prolonged endurance competition. It cites approaches that reduce training volume for three to four days while eating a very high-carbohydrate diet, 8 to 10 g per kg of body mass per day, for one to three days, to maximise muscle glycogen, and says the ability of these strategies to rapidly raise muscle glycogen is currently unquestioned. It also notes that prolonged exercise (longer than 60 to 90 minutes) of moderate to high intensity relies heavily on carbohydrate stores.
This tool multiplies your body mass by 8 and 10 for the daily range and by the number of days for the total. The stand notes that female athletes may need to increase total calorie intake noticeably over the loading days to get similar effects. Grams are carbohydrate, not food weight. It is not a diet plan: planning meals around the grams is a job for a registered dietitian.
Frequently asked questions
How many carbs do I need to carb load for a marathon?
The ISSN stand cites 8 to 10 g per kg of body mass per day for one to three days. For 70 kg that is 560 to 700 g per day.
How many days should I carb load?
The stand describes one to three days of very high carbohydrate intake alongside reduced training volume. The tool lets you pick 1, 2 or 3.
Do I need to carb load for a half marathon or 10K?
The research describes loading for prolonged exercise, longer than about 60 to 90 minutes. The stand does not describe loading for shorter events; the tool tells you when your event is 60 minutes or shorter.
Is carb loading safe if I have diabetes?
Not without medical advice. Large carbohydrate loads affect blood glucose. Ask your doctor or diabetes care team before changing your intake.
Sources
Checked
Ranges are quoted from the sources above and are general research or position-statement figures. Gel, powder and drink contents, spare gels and stop intervals are your own inputs; defaults are placeholders. One kilogram of body mass is treated as one litre of fluid.
Scope
Education only, not medical or dietetic advice. Needs differ by person, event, heat and training, and the published ranges are general. Try any fuelling or hydration plan in training, not for the first time on race day. If you have a medical condition (including diabetes, kidney or heart disease or high blood pressure), are pregnant or breastfeeding, or are under 18, ask your doctor or a registered dietitian first. Stop and get medical help for confusion, vomiting, severe headache, fainting or swelling of the hands and feet during or after a long effort.