Carb loading before a race

Enter your weight and your race. You get the grams of carbohydrate to eat per day in the last two days, plus the race-morning meal. Runs in your browser, nothing is saved or sent.

Units

Where the numbers come from

The load follows the ACSM, Academy of Nutrition and Dietetics and Dietitians of Canada joint statement (Thomas, Erdman and Burke, 2016): 10 to 12 g/kg per day for 36 to 48 hours before events over 90 minutes, and 1 to 4 g/kg in the 1 to 4 hours before the start. The ISSN position stand (Kerksick et al., 2017) allows 8 to 12 g/kg. The calculator shows the bottom of the ACSM range as the single number, and the race-morning meal at 2 g/kg.

Race time sets whether a full load applies: over 90 minutes, a full load; shorter, 7 to 12 g/kg in the 24 hours before. Distance only gives you a pace to sanity-check your finish time. Consensus ranges for healthy adults, not medical advice. The full plan is in marathon carb loading, day by day; once you are racing, use the carbs per hour calculator.

In the app, this comes from your real training

Add your race to the Sweatmeal calendar with its expected duration. For an endurance race of 90 minutes or more, the two days before lift your carb target automatically, then it settles after race day.

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Quick answers

How many grams of carbs should I eat the day before a marathon?
The ACSM joint position statement recommends 10 to 12 g of carbohydrate per kg of bodyweight per day for the 36 to 48 hours before an event longer than 90 minutes. For a 65 kg runner that is 650 to 780 g.
Do I need to carb-load for a half marathon or a short race?
A full load is for events longer than about 90 minutes. For shorter races, eating 7 to 12 g/kg in the 24 hours before is the usual guidance, which the calculator uses.
Why does the Sweatmeal app use 8 g/kg when this says 10?
The app lifts your carb floor to 8 g/kg, the bottom of the ISSN range, for the two days before a long endurance race, and your target can sit above it. This page shows the ACSM 10 to 12 g/kg range. If 10 g/kg is more food than you can eat comfortably, 8 g/kg is a reasonable floor.
Why did I gain weight while carb-loading?
Muscle stores glycogen together with water, so the scale usually rises a little during a load. That is stored fuel, not fat, and it is expected.
Is this medical advice?
No. These are general ranges for healthy adults. Eat foods you have already tried in training, favour low-fibre options, and check with a doctor or dietitian if you have diabetes, a gut condition or any medical concern.