How many carbs before a marathon? A day-by-day carb-load, worked out
Before a marathon, eat 10-12 g of carbohydrate per kg of bodyweight per day for the final 36-48 hours, alongside your taper, then 1-4 g/kg in the 1-4 hours before the start. For a 65 kg runner that is about 650-780 g of carbs a day. The range comes from the ACSM joint position statement for events over 90 minutes.
That’s the whole answer in numbers. The rest of this post turns it into a day-by-day plan you can actually eat. For the broader principle of why a carb-load is a build across race week rather than one pasta dinner, see How to fuel a race without guessing.
Where do these numbers come from?
They come from two position stands that agree closely. The ACSM, Academy of Nutrition and Dietetics and Dietitians of Canada joint statement (Thomas, Erdman and Burke, 2016) lists carbohydrate loading as 10-12 g/kg per 24 hours for 36-48 hours before events over 90 minutes.
The ISSN position stand on nutrient timing (Kerksick et al., 2017) gives a slightly wider 8-12 g/kg/day, and describes the modern approach: reduced training volume for a few days with very high carbohydrate intake for one to three of them. Neither requires the old depletion week.
A marathon is longer than 90 minutes for every runner, so the full load applies whether you finish in 2:30 or 5:30.
What does the day-by-day plan look like?
Here is the week for a 65 kg runner racing on Sunday morning, using 10 g/kg for the load. The training-day range uses the ACSM daily guidance of 5-7 g/kg for moderate training of about an hour a day.
| Day | What’s happening | Carbs per kg | Grams for 65 kg |
|---|---|---|---|
| Wednesday | Taper, short easy run | 5-7 g/kg | 325-455 g |
| Thursday | Taper, short easy run | 5-7 g/kg | 325-455 g |
| Friday | Load day 1, rest or 20 min jog | 10 g/kg | 650 g |
| Saturday | Load day 2, rest or shakeout | 10 g/kg | 650 g |
| Sunday, 3 h before start | Pre-race meal | 2 g/kg | 130 g |
| Sunday, during | 30-60 g/h, up to 90 g/h if over 2.5 h | - | see below |
The arithmetic is simple: bodyweight × grams per kg. 65 × 10 = 650 g. If you push to the top of the range, 65 × 12 = 780 g.
What does 650 g of carbs look like on a plate?
It is a lot more than most runners expect: 650 g of carbs alone is 2,600 kcal (650 × 4). To fit it in without feeling stuffed, lower your fat and fibre for those two days and spread the carbs across five or six meals and snacks.
A rough day, using typical label values (check your own):
- Breakfast: two bagels with jam and a glass of orange juice, about 150 g.
- Mid-morning: a banana and a sports drink, about 60 g.
- Lunch: a large bowl of white rice with lean chicken, about 120 g.
- Afternoon: rice cakes with honey and a fruit yoghurt, about 80 g.
- Dinner: a big plate of pasta with tomato sauce and bread, about 160 g.
- Evening: cereal with milk, about 80 g.
That lands near 650 g. Keep protein moderate rather than high, and favour white, low-fibre versions of everything to protect your gut on race morning.
What should I eat on race morning?
Aim for 1-4 g/kg of carbohydrate 1-4 hours before the start, with the larger amounts further out. The ACSM statement also advises keeping this meal low in fat, fibre and protein to reduce stomach problems.
For our 65 kg runner, 2 g/kg three hours before a 9:00 start is 130 g at 6:00: for example, a bagel with honey, a banana and a sports drink. Eat what you have already tested before long runs.
How many carbs should I take during the race?
Take 30-60 g per hour for efforts of 1-2.5 hours, and up to 90 g per hour beyond about 2.5 hours, per the same ACSM table. Jeukendrup (2014) explains why: a single sugar source is absorbed at up to about 60 g/h, while higher rates need mixed glucose-fructose products.
A 3:45 runner taking 60 g/h needs about 225 g across the race (3.75 × 60). That is roughly nine gels of 25 g each; check your brand’s label. Train with this amount before race day, because gut tolerance is trainable but not instant.
How sure are these numbers?
They are ranges from consensus statements, not a prescription for your physiology. Women, very light runners and anyone with a history of gut issues may find the top of the range hard to eat. The 8 g/kg lower bound in the ISSN stand is a reasonable floor if 10-12 g/kg is too much food.
Expect the scale to rise a little during the load: glycogen is stored with water. That is fuel, not fat.
How Sweatmeal handles marathon week
In Sweatmeal you add the marathon to the race calendar with its expected duration. For an endurance race of 90 minutes or more, the two days before it lift your carb target to a floor of 8 g/kg of bodyweight, the bottom of the ISSN range, then let it settle after race day. If you are aiming for the full 10-12 g/kg, treat 8 as the minimum and eat above it. The calendar and targets are free; with Pro, the coach names your next meal in grams as the load goes on. The calculation behind every number is on our methodology page.