Carb Loading Calculator: Grams of Carbohydrate per kg of Body Weight

Carb loading means eating extra carbohydrate in the last day or two before a long race, while you cut back training, so your muscles start with as much stored glycogen as they can hold. Glycogen is the carbohydrate your muscles burn at race pace, and the supply is limited. In a review of the loading research, Hawley and colleagues (1997) found that exhaustion in long events tends to arrive as muscle glycogen runs critically low, and that starting with more of it postpones fatigue by about 20 percent in events lasting longer than 90 minutes.

This calculator turns the published amounts into grams for your body weight. It uses the guidelines Louise Burke and colleagues set out (Burke et al. 2011), which Table 1 of Burke's open 2015 review summarizes (Burke 2015): 10 to 12 g of carbohydrate per kilogram of body weight a day for 36 to 48 hours, with a training taper. The 2016 joint position stand of the American College of Sports Medicine, the Academy of Nutrition and Dietetics and Dietitians of Canada (Thomas, Erdman and Burke 2016) gives the same range, as a 2026 meta-analysis of loading trials notes (Jones et al. 2026). The calculator also checks whether your race is long enough to need a load and lays out a race-week plan. It gives you targets in grams, and it does not count food or plan meals.

How many carbs to carb load

The amount scales with your body weight. Burke's guidelines give it per kilogram per day, so the arithmetic takes two steps:

Grams per day = body weight in kg × 10 to 12In pounds: body weight in lb × 4.5 to 5.4Total = grams per day × days of loading

1. Check the race length. Load only if you expect to take 90 minutes or more. A marathon in 4 hours 30 minutes qualifies.
2. Convert to kilograms. Divide pounds by 2.205: 154 lb is 69.9 kg.
3. Multiply by 10 and by 12. That gives 699 and 838 g, which the calculator rounds to 700 to 840 g a day. The middle of the range, 11 g/kg, is 770 g.
4. Multiply by the days. Two days of loading come to 1,400 to 1,680 g of carbohydrate in all.

In metric there is nothing to convert: a 60 kg runner needs 600 to 720 g a day, and an 80 kg runner needs 800 to 960 g.

The range is a target rather than a cliff edge. After pooling 63 loading studies in a 2026 meta-analysis, Jones and colleagues recommend more than 8 g/kg a day for 36 to 48 hours to raise glycogen stores before competition, a lower floor than the guideline's 10 g/kg. If 12 g/kg is more than you can comfortably eat, the lower end of the range should still raise your stores.

Who needs to carb load, and who does not

Carb loading is for events that last longer than about 90 minutes: marathons, most half marathons, long triathlons, long bike rides and ultramarathons. Burke's guidelines apply it to events that usually last more than 90 minutes, the events in which muscle glycogen runs low.

Shorter races do not need it. Hawley's review found that raising muscle glycogen above its normal resting level made little or no difference to a single hard effort of under 5 minutes, or to moderate running or cycling lasting 60 to 90 minutes. A study by Sherman and colleagues (1981) tested it directly. Trained runners tapered for six days on one of three diets, and the two loading diets raised muscle glycogen to 203 and 207 mmol/kg (wet weight) against 159 for a mixed diet, yet their times for a 20.9 km run did not differ. The authors concluded that loading was of no benefit to trained runners at that distance.

So a 5K or 10K, which most people finish well under 90 minutes, needs no load. Eat your normal meals the day before and a familiar breakfast on race morning; our guide on what to eat before a 5K times that breakfast. The calculator shows no load for any finish time under 90 minutes.

Carb loading is also different from your everyday diet. The macro calculator sets daily protein, carbohydrate and fat for body composition goals, while a carb load is a short change for one race, after which you go back to normal eating.

Carb loading for a marathon

A marathon is the classic case. Start 36 to 48 hours before the gun: for a morning race, begin at breakfast two days before (48 hours) or by dinner that evening (36 hours), and eat 10 to 12 g/kg on each full day. Cut training right back over the same days, because Burke's protocol includes a taper. Most marathon plans already end with one, and our guide on how to train for a marathon builds a three-week taper into its 18 weeks. Enter your goal time and this page works as a marathon carb loading calculator, with each day of race week laid out in grams.

The day before matters most. In a study of 257 runners in the 2009 London Marathon, Atkinson and colleagues (2011) found that those who reported eating more than 7 g/kg of carbohydrate the day before ran faster overall, and held their pace better through the race, than those who ate less. In their analysis, carbohydrate eaten the day before predicted race speed independently of sex, body mass index and training distance. It was an observational study of what runners reported, so it shows an association rather than proof, but it points the same way as the controlled trials.

On race morning, eat 1 to 4 g/kg in the 1 to 4 hours before the start, and in a race longer than 2.5 hours take up to 90 g of carbohydrate an hour, as the next sections explain. Afterward, our article on how long it takes to recover from a marathon covers refueling and the weeks that follow.

Carb loading for a half marathon

Whether to load for a half marathon depends on your finish time, not the distance. If you expect to take 90 minutes or longer, a load at 10 to 12 g/kg for 36 to 48 hours fits, or one day at the same rate on a rest day. If you will finish in under 90 minutes, the studies above suggest a load adds nothing, and normal meals plus a good race-morning breakfast are enough. Enter your expected time and the calculator decides. Our half marathon training plan covers the training side, including when to start fueling on long runs.

One-day and three-day carb loading

Two days is the standard, but two other plans have evidence behind them, and the classic depletion phase is no longer needed.

One day on a rest day

Bussau and colleagues (2002) had eight endurance-trained men eat 10 g/kg of high-glycemic-index carbohydrate a day for three days while doing no exercise. Muscle glycogen rose from 95 to 180 mmol/kg (wet weight) after the first day, an 89 percent rise, and stayed there for the next two. The authors concluded that trained athletes can reach maximal stores within 24 hours if they rest. The ISSN position stand on nutrient timing (Kerksick et al. 2017) lists the same one-day approach. The 2026 meta-analysis is more cautious. It argues that the load in Bussau's study really ran for about 36 hours, because the athletes' last training session ended about 12 hours before it began, and it notes that in most cases one day raises stores about 1.5-fold. So load for one day only when you have to, keep it a rest day and choose high-glycemic foods.

Three days with a taper

Sherman's 1981 plan tapered training over six days, with runs of 90, 40, 40, 20 and 20 minutes and then a rest day, and switched to a 70 percent carbohydrate diet for the last three. The ISSN position stand now gives 8 to 10 g/kg a day for one to three days of reduced training. The calculator's 3-day option uses 8 to 10 g/kg a day, which is less per day than a 2-day load but more in total.

Skip the depletion phase

The original carb load began with three or four days of hard training on very little carbohydrate before the high-carbohydrate days, the classic plan the ISSN position stand describes. It is not needed. In Sherman's study, the plan without depletion reached 203 mmol/kg against 207 for the classic one, and the 2026 meta-analysis concluded that a depleting phase is not a prerequisite for endurance-trained athletes.

The day before, race morning and during the race

The day before. In every plan here, the day before the race is a full loading day: 10 to 12 g/kg on a 1-day or 2-day load, or 8 to 10 g/kg on a 3-day load. Spreading it over the whole day is easier than saving it for one big dinner.

Race morning. Burke's guidelines add a pre-event meal of 1 to 4 g/kg of carbohydrate eaten 1 to 4 hours before events that last longer than about 45 minutes. For the default 154 lb runner, that is about 70 to 280 g. A large breakfast needs time to settle, so the closer you eat to the start, the smaller the meal. Our guide on what to eat before a long run gives meal ideas by how much time you have.

During the race. Loading fills the tank before the start, and carbohydrate during the race tops it up. Burke and colleagues (2011) recommend 30 to 60 g an hour in events of 1 to 2.5 hours and up to 90 g an hour in events longer than 2.5 hours. They add that in hard races of about an hour, even small amounts, or rinsing your mouth with a sports drink, can help. The calculator applies these bands to your finish time. For fluids, the sweat rate calculator works out how much to drink per hour.

Carb loading chart by body weight

The chart gives grams of carbohydrate per day and in total for a 2-day load at 10 to 12 g/kg, per day for a 3-day load at 8 to 10 g/kg, and the race-morning meal at 1 to 4 g/kg. Values are rounded to the nearest 5 g, as in the calculator.

What to eat when carb loading

Several hundred grams of carbohydrate a day is a lot of food, so choose foods that pack carbohydrate into a small volume: white rice, pasta, bread, bagels, potatoes, breakfast cereal, pancakes, fruit juice, honey, jam and sports drinks. Bussau's one-day trial used high-glycemic-index foods, and the 2026 meta-analysis recommends them when the load is short.

A few practical habits make the target reachable. Eat more often rather than much bigger meals, keep fat and fiber modest so they do not crowd out the carbohydrate, and count drinks such as juice, milk and sports drinks, which add grams without filling you up. Stick to foods you know agree with you, and try your loading days once before a long training run so that race week holds no surprises.

Food labels list carbohydrate in grams, which is the number to add up. FitCraft coaches workouts and does not count food or plan meals. If you want an app to log your grams, our comparison of FitCraft and MyFitnessPal explains what each one does and why some people use both.

Will carb loading make you gain weight?

Yes, for a few days, and most of the gain is water. Muscle stores glycogen together with water: Fernández-Elías and colleagues (2015) estimated at least 3 g of water for every gram of glycogen, and Shiose and colleagues (2016) cite earlier estimates of 2.7 to 4 g. In Shiose's study, three days at 12 g/kg a day more than doubled muscle glycogen, from 72.7 to 169.4 mmol/kg (wet weight), and raised total body water from 39.3 to 40.2 kg, close to 2 lb.

The extra water also shows up on body composition scans. When Bone and colleagues (2017) had trained male cyclists eat 12 g/kg a day for 48 hours, a DXA scan read their lean mass 3.0 percent higher, and total body water rose 2.3 percent. So expect the scale to read higher on race morning, and do not try to lose weight in race week. The extra weight is stored fuel and the water held with it.

Carb loading for women

Women load as well as men when they eat enough. Early studies suggested otherwise. In a 1995 study by Tarnopolsky and colleagues, raising carbohydrate from 55 to 60 percent of energy to 75 percent for four days raised muscle glycogen by 41 percent in men and not at all in women, and improved the men's performance time in a hard cycling test by 45 percent against 5 percent for the women. A follow-up study (Tarnopolsky et al. 2001) found that women raised their glycogen only when they also ate about a third more energy, and concluded that a low energy intake may explain the gap.

When intake is set per kilogram, the difference disappears. James and colleagues (2001) gave men and women 12 g of carbohydrate per kg of lean body mass a day for three days. Glycogen rose from 108 to 193 and from 111 to 202 mmol/kg (wet weight) in women tested in the post-menstrual and pre-menstrual phases, and from 109 to 183 in men. The 2026 meta-analysis agrees that men and women have the same capacity to load when intake is matched, though only 12 percent of the people in the trials it reviewed were women. The ISSN position stand adds that female athletes may need to raise their total calorie intake substantially on loading days. So aim for the grams per kilogram, not a percentage of your usual calories.

How accurate is this carb loading calculator?

The calculator does the arithmetic exactly, so the accuracy question is how well the guideline predicts what happens in your muscles and in your race. The per-kilogram amounts reliably raise glycogen, the size of the rise varies a great deal between people, and the performance gain is real in long events but modest.

How much muscle glycogen goes up

Every controlled study here found a large rise, although the numbers depend on the starting point and on how glycogen was measured. In wet-weight terms, Bussau's one-day load took glycogen from 95 to 180 mmol/kg, Shiose's three-day load from 72.7 to 169.4 and James's three-day load in men from 109 to 183. Pooling 18 studies, the 2026 meta-analysis by Jones and colleagues found that raising intake from below to above 6.5 g/kg a day lifted glycogen by 191.9 mmol/kg of dry muscle on average (95 percent confidence interval 142.8 to 241.1). That is about half again above the typical starting level of roughly 400 mmol/kg of dry muscle the authors give. The pooled rise was 207.7 mmol/kg after 24 hours of loading and 255.0 after 48 hours.

How much faster it makes you

Hawley's 1997 review put the gain at about 20 percent more time before fatigue in events longer than 90 minutes, and a 2 to 3 percent improvement in performance over a set distance, with no benefit in moderate exercise lasting 60 to 90 minutes. If 2 to 3 percent carried over to a 4 hour 30 minute marathon, it would be about 5 to 8 minutes.

Not every trial found a gain. In a placebo-controlled study by Burke and colleagues (2000), seven well-trained cyclists ate 9 or 6 g/kg a day for three days before a 100 km time trial, and also had a 2 g/kg breakfast and 1 g/kg an hour of carbohydrate during the ride. Loading raised muscle glycogen (572 against 485 mmol/kg dry weight), but the riders finished in 147.5 and 149.1 minutes, a difference too small to rule out chance. When you eat a good breakfast and fuel during the race, loading may add less than the older studies suggest. Sherman's 20.9 km run showed no gain either, and the London Marathon finding (Atkinson 2011) is an association, not a trial.

How much people differ

The spread between people is large. The 2026 meta-analysis found very high heterogeneity between studies (I² = 94 percent) and described high variability in muscle glycogen between individuals eating similar amounts. In endurance-trained people, carbohydrate intake explained about half of the differences in glycogen (r² = 0.49), and in recreationally active people about a third (r² = 0.33). Within single studies, Shiose's eight subjects ended at 169.4 mmol/kg with a standard deviation of 55.9, a third of the average, and James's men ended at 183 with a standard deviation of 25.

Most of these studies tested lean, trained men, so the per-kilogram figures fit them best. If you carry more body fat, scaling by total body weight gives a larger number than the lean-mass dosing James used, so the lower end of the range is a sensible start. Treat the result as a target for one or two days, rehearse it before a long training run, and adjust by how your stomach and your legs respond.

Worked examples: seven races through the calculator

Each row runs the calculator for a different runner or rider. During the race shows grams per hour, with the total for the finish time in brackets.

Two patterns stand out. The 145 lb half marathoner who finishes in 1 h 25 min gets no load, while the 130 lb runner who takes 2 h 10 min loads, because finish time decides, not distance. And the 3-day plan for the 180 lb marathoner gives less per day than a 2-day plan would (655 to 815 g against 815 to 980 g), but more in total.

When to ignore this calculator

Carb loading is a short, high-carbohydrate change for healthy adults before a long event. In these cases, get a plan from a clinician or a registered dietitian instead.

• Diabetes or prediabetes. Several hundred grams of carbohydrate a day changes blood sugar and medication needs. Plan any load with your diabetes care team.
• Digestive conditions. Irritable bowel syndrome, inflammatory bowel disease, celiac disease or a history of gut trouble on runs can flare with a sudden jump in carbohydrate. A sports dietitian can pick foods that suit you, and our article on why your stomach hurts when you run covers the common causes.
• An eating disorder, now or in the past. Counting grams and eating to a target can be harmful. Work with your treatment team.
• Pregnancy. Energy and carbohydrate needs change during pregnancy. Ask your obstetric care team.
• Teenagers. The loading studies tested adults. Young athletes should get advice from a pediatric or sports dietitian.
• A diet your doctor prescribed. If you follow a low-carbohydrate, low-sugar or kidney diet for a medical reason, keep to it and ask before changing it for a race.

If you feel sick, bloated or dizzy during a load, scale it back. A smaller load you can eat comfortably is better than a bigger one that upsets your stomach on race morning.

Related reading

References

1. Burke LM. "Re-examining high-fat diets for sports performance: did we call the 'nail in the coffin' too soon?" Sports Med. 2015;45(Suppl 1):33-49. doi:10.1007/s40279-015-0393-9, PMC4672014. Table 1 gives the loading, pre-event and during-event protocols from reference 2.
2. Burke LM, Hawley JA, Wong SH, Jeukendrup AE. "Carbohydrates for training and competition." J Sports Sci. 2011;29(Suppl 1):S17-S27. doi:10.1080/02640414.2011.585473, PubMed 21660838. The full text is not open access; its loading figures are reproduced in Table 1 of reference 1.
3. Thomas DT, Erdman KA, Burke LM. "American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance." Med Sci Sports Exerc. 2016;48(3):543-568. doi:10.1249/MSS.0000000000000852, PubMed 26891166. The full text is not open access; its 10 to 12 g/kg for 36 to 48 hours is cited in reference 8.
4. Kerksick CM, Arent S, Schoenfeld BJ, et al. "International society of sports nutrition position stand: nutrient timing." J Int Soc Sports Nutr. 2017;14:33. doi:10.1186/s12970-017-0189-4, PMC5596471
5. Bussau VA, Fairchild TJ, Rao A, Steele P, Fournier PA. "Carbohydrate loading in human muscle: an improved 1 day protocol." Eur J Appl Physiol. 2002;87(3):290-295. doi:10.1007/s00421-002-0621-5, PubMed 12111292
6. Sherman WM, Costill DL, Fink WJ, Miller JM. "Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance." Int J Sports Med. 1981;2(2):114-118. doi:10.1055/s-2008-1034594, PubMed 7333741
7. Hawley JA, Schabort EJ, Noakes TD, Dennis SC. "Carbohydrate-loading and exercise performance. An update." Sports Med. 1997;24(2):73-81. doi:10.2165/00007256-199724020-00001, PubMed 9291549
8. Jones RO, Areta JL, Fortis HO, Pugh J, Louis JB. "Dietary carbohydrate intake and skeletal muscle glycogen: a systematic review and meta-analysis to determine optimal carbohydrate loading strategies." Scand J Med Sci Sports. 2026;36(10):e70379. doi:10.1111/sms.70379, PMC13633599
9. Burke LM, Hawley JA, Schabort EJ, St Clair Gibson A, Mujika I, Noakes TD. "Carbohydrate loading failed to improve 100-km cycling performance in a placebo-controlled trial." J Appl Physiol. 2000;88(4):1284-1290. doi:10.1152/jappl.2000.88.4.1284, PubMed 10749820
10. Atkinson G, Taylor CE, Morgan N, Ormond LR, Wallis GA. "Pre-race dietary carbohydrate intake can independently influence sub-elite marathon running performance." Int J Sports Med. 2011;32(8):611-617. doi:10.1055/s-0031-1273739, PubMed 21590642
11. James AP, Lorraine M, Cullen D, Goodman C, Dawson B, Palmer TN, Fournier PA. "Muscle glycogen supercompensation: absence of a gender-related difference." Eur J Appl Physiol. 2001;85(6):533-538. doi:10.1007/s004210100499, PubMed 11718281
12. Tarnopolsky MA, Atkinson SA, Phillips SM, MacDougall JD. "Carbohydrate loading and metabolism during exercise in men and women." J Appl Physiol. 1995;78(4):1360-1368. doi:10.1152/jappl.1995.78.4.1360, PubMed 7615443
13. Tarnopolsky MA, Zawada C, Richmond LB, Carter S, Shearer J, Graham T, Phillips SM. "Gender differences in carbohydrate loading are related to energy intake." J Appl Physiol. 2001;91(1):225-230. doi:10.1152/jappl.2001.91.1.225, PubMed 11408434
14. Shiose K, Yamada Y, Motonaga K, Sagayama H, Higaki Y, Tanaka H, Takahashi H. "Segmental extracellular and intracellular water distribution and muscle glycogen after 72-h carbohydrate loading using spectroscopic techniques." J Appl Physiol. 2016;121(1):205-211. doi:10.1152/japplphysiol.00126.2016, PubMed 27231310
15. Fernández-Elías VE, Ortega JF, Nelson RK, Mora-Rodriguez R. "Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans." Eur J Appl Physiol. 2015;115(9):1919-1926. doi:10.1007/s00421-015-3175-z, PubMed 25911631
16. Bone JL, Ross ML, Tomcik KA, Jeacocke NA, Hopkins WG, Burke LM. "Manipulation of muscle creatine and glycogen changes dual X-ray absorptiometry estimates of body composition." Med Sci Sports Exerc. 2017;49(5):1029-1035. doi:10.1249/MSS.0000000000001174, PubMed 28410328

How this calculator differs from typical carb loading calculators

Most online carb load calculators multiply body weight by a single number, often 8 or 10 g/kg, for a fixed two or three days, and stop there. Few say where the number comes from, whether your race is long enough to need a load at all, or how much the result varies between people. Fewer still mention that a placebo-controlled trial found no significant gain when riders also ate breakfast and fueled during the race.

This calculator uses the 10 to 12 g/kg for 36 to 48 hours that Burke's guidelines and the 2016 joint position stand set out, with sourced options for a one-day load on a rest day and a three-day load at 8 to 10 g/kg. It shows no load for finish times under 90 minutes, adds the race-morning meal at 1 to 4 g/kg and race-day carbohydrate by finish time, and gives the per-pound amounts for US readers. The accuracy section reports what the studies found, including how much people differ in the 2026 meta-analysis.