How carb loading works
Your muscles store carbohydrate as glycogen, and glycogen is the fuel that runs out around the 30 km mark of a marathon — the dreaded "wall". Carbohydrate loading tops those stores up as high as possible in the days before a long race, so you have more fuel in the tank when it matters.
The modern approach is simple: in the final 1–3 days, while your training tapers right down, eat 8 to 12 grams of carbohydrate per kilogram of body weight per day. The old "depletion" phase — a week of low-carb misery first — is no longer considered necessary.
Carbs per day by body weight
Daily carbohydrate target for a two-to-three day load, at the low (8 g/kg), standard (10 g/kg), and high (12 g/kg) ends of the range. These are the values this calculator produces.
| Body weight | 8 g/kg | 10 g/kg | 12 g/kg |
|---|---|---|---|
| 50 kg (110 lb) | 400 g | 500 g | 600 g |
| 60 kg (132 lb) | 480 g | 600 g | 720 g |
| 70 kg (154 lb) | 560 g | 700 g | 840 g |
| 80 kg (176 lb) | 640 g | 800 g | 960 g |
| 90 kg (198 lb) | 720 g | 900 g | 1,080 g |
These numbers are large — often two to three times normal intake. Hitting them means making carbohydrate the centre of every meal and snack, and leaning on liquids like juice and sports drinks to top up without feeling stuffed.
Best foods for carb loading
- Staples: white rice, pasta, bread, bagels, potatoes, oats.
- Fruit: bananas, ripe fruit, dried fruit, fruit juice.
- Liquids: sports drinks and juice help you hit big totals without feeling over-full.
- Keep moderate: fibre, fat, and protein — they are filling and can upset the stomach in large amounts before a race.
Expect the scale to rise 1–2 kg: glycogen binds water, and that stored water is race-day hydration, not fat. It reverses as you burn glycogen during the race.
Nail the whole race build
The Running Genie plans your taper, long runs, and race strategy — so your carb load lands on top of a properly prepared body.
Frequently asked questions
How many carbs should I eat when carb loading?
The evidence-based target is 8 to 12 grams of carbohydrate per kilogram of body weight per day, in the 1 to 3 days before a long race. A 70 kg runner would aim for roughly 560 to 840 grams per day. This calculator works out your exact numbers from your weight.
How many days should I carb load before a marathon?
For most runners, 1 to 3 days is enough. The classic depletion-then-load protocol is largely outdated; modern practice is to raise carbohydrate intake in the final 2 to 3 days while tapering training, which tops up muscle glycogen without a depletion phase.
Does carb loading make you gain weight?
You may see the scale rise by 1 to 2 kg, because each gram of stored glycogen holds about 3 grams of water. This is expected and useful — the extra glycogen and water are fuel and hydration for race day, not fat gain. It reverses as you use the glycogen.
What foods are best for carb loading?
Choose easily digested, lower-fibre carbohydrates: rice, pasta, bread, potatoes, oats, bananas, and sports drinks. Keep fat and fibre moderate to avoid stomach upset, and spread the carbohydrate across several meals and snacks rather than a few enormous plates.
Do I need to carb load for a 5K or 10K?
No. Carbohydrate loading only benefits events long enough to deplete muscle glycogen — roughly 90 minutes or more of hard running. For a 5K or 10K, normal eating with a decent carbohydrate meal the night before and a light carb snack pre-race is all you need.
Related running calculators
Plan the perfect race week
Download The Running Genie for a marathon plan with a proper taper, pacing, and race-day strategy — so your carb load actually pays off.
