Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Carb Loading Is Calculated
Carb loading means eating more carbohydrate than usual, while training less, in the days before a long event. The aim is to fill your muscles with glycogen, the stored form of carbohydrate that fuels hard endurance exercise. Targets are set by body weight, in grams of carbohydrate per kilogram (g/kg), so a heavier athlete needs more grams than a lighter one.
What a Carb Loading Target Measures
It measures how much carbohydrate to eat in the run-up to one event, not your everyday intake. For a daily target on normal training days, use the Carbohydrate Calculator instead. This tool does not measure your glycogen, count calories or tell you which foods to eat.
The Formula
Daily carbs (g) = body weight (kg) x 10 to 12 g/kg, for 36 to 48 hours before an event over 90 minutes
Race morning (g) = body weight (kg) x 1 to 4 g/kg, eaten 1 to 4 hours before an event over 60 minutes
During the event (g) = grams per hour x event hours
These numbers come from the 2016 joint position of the American College of Sports Medicine, the Academy of Nutrition and Dietetics and Dietitians of Canada¹.
How This Calculator Computes Your Result
Enter your body weight (pounds or kilograms), event type, expected duration, number of loading days (1 to 3), a loading target of 10, 11 or 12 g/kg, and how many meals and snacks you plan per day. Pounds are converted with 1 lb = 0.45359237 kg. All gram results are rounded to the nearest 5 g.
You get a daily carb target, the total for your loading days, an equal split across your meals and snacks, a race-morning range and a during-race range in grams per hour with a total for the event. For example, a 150 lb (68 kg) runner with a 3 hour 45 minute marathon, loading for 2 days at 10 g/kg, gets 680 g per day (about 135 g at each of 5 meals and snacks), 70 to 270 g on race morning, and up to 90 g per hour during the race.
What Your Result Means
Whether loading applies depends on how long your event lasts¹:
Event duration | What the calculator shows | Daily carbohydrate |
90 minutes or less | Loading not needed. Normal fueling for the 24 hours before | 7 to 12 g/kg |
Over 90 minutes | Carb loading for 1 to 3 days | 10 to 12 g/kg |
The during-race target also depends on duration¹:
Event duration | Carbs during the event |
Under 45 minutes | Not needed |
45 to 75 minutes | Small amounts, including a mouth rinse |
1 to 2.5 hours (including stop-and-start sports) | 30 to 60 g per hour |
Over 2.5 to 3 hours | Up to 90 g per hour |
Two bands overlap between 60 and 75 minutes. For a stop-and-start team sport, the calculator uses 30 to 60 g per hour from 60 minutes, because the position names these sports in that band¹. For other events, it uses that band only above 75 minutes.
Does Carb Loading Work?
For the right events, yes. A 1997 review found that loading had little effect on short, intense bouts under 5 minutes or on moderate running or cycling lasting 60 to 90 minutes⁴. In events over 90 minutes, higher starting glycogen postponed fatigue by about 20 percent, and in all-out endurance efforts, performance improved by 2 to 3 percent⁴.
You may not need a long load. In 8 trained men who rested, 1 day at 10 g/kg raised muscle glycogen from 95 to 180 mmol per kg of muscle, and it did not rise further over the next 2 days⁵. A 2026 study in 11 endurance-trained adults compared 6, 8 and 10 g/kg a day for 48 hours⁶. Glycogen was highest at 10 g/kg, and 6 and 8 g/kg did not differ from each other⁶. That is one reason this calculator starts at 10 g/kg.
Carbs During the Race
For longer events, 30 to 60 g per hour is an appropriate target, and events over 2.5 hours may benefit from up to 90 g per hour². The body can only use about 60 g per hour of a single type of sugar, such as glucose³. Mixing glucose and fructose raised the rate of use by up to 75 percent in the studies reviewed, which is how higher intakes become usable³. These guidelines were written for well-trained athletes, and people working at a lower intensity may need less³. The calculator also shows a per 20 minute amount, so you can plan small, regular feeds.
Common Carb Loading Mistakes
Loading for a short race. Under 90 minutes, normal fueling of 7 to 12 g/kg is the guideline¹.
Keeping training high. Loading pairs extra carbohydrate with a lighter training load¹.
Eating high-fiber, high-fat or high-protein foods. Lower-fiber carbohydrate foods can help you meet high targets, and high-fat, high-protein or high-fiber choices before the start can raise the risk of stomach upset¹.
Trying it for the first time on race week. Both the position and a 2014 review advise practicing your fueling plan in training¹ ³. In the 2026 study, the highest intake raised the feeling of fullness⁶.
Daily Carb Loading Target by Body Weight
Grams of carbohydrate per loading day at each target, plus the race-morning range. Pick your weight to read across.
| Body weight | Carbohydrate (g) | |||
|---|---|---|---|---|
| 10 g/kg | 11 g/kg | 12 g/kg | Race morning, 1 to 4 g/kg | |
| 110 lb | 500 | 550 | 600 | 50–200 |
| 130 lb | 590 | 650 | 710 | 60–235 |
| 150 lb | 680 | 750 | 815 | 70–270 |
| 170 lb | 770 | 850 | 925 | 75–310 |
| 190 lb | 860 | 950 | 1,035 | 85–345 |
| 210 lb | 955 | 1,050 | 1,145 | 95–380 |
| 230 lb | 1,045 | 1,150 | 1,250 | 105–415 |
Use the arrow keys to move between cells.
A Note on Accuracy
These are guideline ranges, not a measured need. They come mostly from studies of trained endurance athletes, and your best amount depends on your event, intensity, gut comfort and training. The calculator assumes you taper during the loading days and does not count calories, protein, fat or fluid. It is not built for people under 18. If you have diabetes or another condition that affects how you handle carbohydrate, plan any loading with your doctor or a sports dietitian.
Frequently Asked Questions
How many carbs should I eat when carb loading?
The guideline is 10 to 12 g of carbohydrate per kilogram of body weight per day for 36 to 48 hours before an event over 90 minutes¹. For a 68 kg (150 lb) athlete, that is about 680 to 815 g a day.
How many days before a marathon should you carb load?
The joint position uses 36 to 48 hours, or about 2 days, with lighter training¹. A small study found 1 day at 10 g/kg with rest also raised glycogen to a high level⁵.
Do you need to carb load for a half marathon?
Only if you expect to take more than 90 minutes. For faster finishes, normal fueling of 7 to 12 g/kg in the 24 hours before is the guideline¹.
Does carb loading actually work?
In events over 90 minutes, higher glycogen has been shown to delay fatigue by about 20 percent and improve all-out performance by 2 to 3 percent, but it does little for shorter events⁴. The calculator's numbers are estimates for trained athletes, so test them in training first.
Sources
Nutrition and Athletic Performance, Thomas et al., 2016
Carbohydrates for Training and Competition, Burke et al., 2011
Carbohydrate Intake During Exercise, Jeukendrup, 2014
Carbohydrate-Loading and Exercise Performance, Hawley et al., 1997
Carbohydrate Loading in Human Muscle: An Improved 1 Day Protocol, Bussau et al., 2002
Dose-Response of Carbohydrate Intake on Muscle Glycogen, Jones et al., 2026