Find out how much carbohydrate to eat before your race, and get a day-by-day plan built around your event, your body weight and the foods you like.
General guidance only. Practise your carb load before a long training run or a lower-priority race first.
Choose a marathon, half marathon, ultra, triathlon, cycling or another endurance event, and set your expected finish time.
Your body weight, how long you have to load (24, 36 or 48 hours), how many carbs you usually eat, and whether big carb meals upset your stomach.
Optional. Foods you love, foods to avoid, allergies, dietary preference and meal style, so the plan fits how you actually eat.
Your daily carbohydrate target in grams, a day-by-day timeline and the foods to hit it. Download it as a PDF or have it emailed.
For races longer than about 90 minutes, current sports nutrition guidance is 10–12 g of carbohydrate per kg of body weight a day for the 36–48 hours before the start (Thomas, Erdman & Burke 2016). A 2026 meta-analysis found that more carbohydrate meant more stored muscle glycogen, and recommended more than 8 g/kg a day for 36–48 hours (Jones et al. 2026).
For a 70 kg runner, 10 g/kg is 700 g of carbohydrate a day. This carb loading calculator does the maths for you and turns it into a plan you can actually eat.
It depends on how long you’ll be racing, not the distance:
So a 1:25 half marathoner doesn’t need a full load, but a 2:30 half marathoner probably does. For marathons, Ironman and ultras, loading is on the table for everyone.
Want the evidence behind all this, including whether carb loading actually makes you faster? Read Carb Loading for a Marathon: What the Science Actually Says. Once you’ve loaded, use the Race-Day Fuel Calculator for your carbohydrate, fluid and sodium targets during the race.
It applies published grams-per-kilogram guidance to your body weight, event length and loading window. Your real needs also depend on your training status, how well your gut copes and what you eat during the race, so treat the numbers as a well-informed starting point and test them in training.
36–48 hours before the start. For a Sunday morning marathon, that means Friday morning or lunchtime. Loading for longer than that doesn’t seem to add anything.
Yes. Trained athletes eating around 10 g/kg while resting raised their muscle glycogen substantially in 24 hours (Bussau et al. 2002). Choose the 24-hour option in the calculator if that’s all the time you have.
Not much, if at all. In a 2026 trial, body mass after 48 hours at 10 g/kg a day was no different to 6 g/kg (Jones et al. 2026). If the scales do move, it’s stored fuel and water, not fat.
Only if you’ll be running for more than about 90 minutes. Faster runners can “fuel up” the day before instead. Pick your event and finish time in the calculator and it will tell you which applies.
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These tools give you a solid starting point. If you want your fuelling built around your training, your gut and your week, work with me directly. I’m Dr Paul Fairbairn, a SENr-registered performance nutritionist working with athletes, adventurers and anyone taking on something big.
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