Macro Calculator

How the split is worked out

Each macronutrient carries a fixed amount of energy per gram: 4 kcal for protein, 4 for carbohydrate and 9 for fat — the Atwater factors behind every nutrition label. Alcohol, at 7 kcal per gram, counts towards calories but is not a nutrient target. Because fat is more than twice as energy-dense, a percentage split and a gram split can look very different: 30% of your calories from fat is far fewer grams than 30% from carbohydrate.

The calculator sets the three in the order dietitians usually do. Protein comes first, scaled to body weight, because the body's need for it tracks its size rather than how much you eat. Fat comes second, as a share of calories. Carbohydrate is the remainder — the most flexible of the three.

A worked example: 80 kg, a 2,209 kcal target (maintenance of 2,759 kcal less 550 kcal for 0.5 kg a week), 1.6 g/kg of protein and 30% fat. Protein is 80 × 1.6 = 128 g, or 512 kcal. Fat is 30% of 2,209 = 663 kcal, which at 9 kcal a gram is 74 g. Carbohydrate is what remains: 2,209 − 512 − 663 = 1,034 kcal, or 259 g. Over four meals, that is 32 g of protein, 65 g of carbohydrate and 18 g of fat each.

How much protein: the evidence behind the levels

The adult RDA — 0.8 g per kilogram of body weight a day — is the amount that prevents deficiency in almost everyone, not the amount that is best for an active person. It is the bottom of the menu here.

For people who train, the commonly used range is about 1.2 to 2.2 g/kg. The top of it has a specific origin: a 2018 meta-analysis by Morton and colleagues in the British Journal of Sports Medicine, pooling 49 trials of resistance training, found that gains in muscle mass levelled off at around 1.6 g/kg a day, with the upper confidence limit near 2.2 g/kg. Most people who lift get nearly all of the benefit at 1.6; 2.2 is the make-sure figure.

During a calorie deficit, more protein helps you keep muscle while losing fat, and protein is the most filling of the three macronutrients, which is why many fat-loss plans sit towards the upper end of the range.

One adjustment matters. If you carry a lot of body fat, grams per kilogram of total weight overstates your need, because fat tissue needs little protein, so many dietitians base the figure on a goal weight instead. Here, choose a lower level to get the same grams: 1.2 g/kg of a 100 kg current weight is 120 g, the same as 1.5 g/kg of an 80 kg goal weight.

Fat and carbohydrate: the flexible part

The 20–35% range for fat comes from the US National Academies' Acceptable Macronutrient Distribution Ranges, which also give 45–65% for carbohydrate and 10–35% for protein. It balances getting enough essential fats and fat-soluble vitamins against keeping saturated fat and total energy in check.

Within that range, the balance between fat and carbohydrate matters much less for weight than total calories do. The DIETFITS trial (JAMA, 2018) assigned 609 adults to a healthy low-fat or a healthy low-carbohydrate diet for a year and found no meaningful difference in the weight they lost. Choose the split you can keep to.

Training changes the picture. Endurance athletes doing long sessions need far more carbohydrate than a 30% fat share leaves room for — sports-nutrition guidelines scale it to training volume, from about 3 g per kilogram a day for light training to 8–12 g/kg for very heavy endurance work.

The calculator also flags carbohydrate below 130 g a day, the adult RDA set to cover the brain's glucose use. A low-carbohydrate diet goes below it on purpose; the note is there so it does not happen by accident.

Using the numbers day to day

Treat the grams as targets for the week rather than rules for every meal. Hitting your protein most days matters more than matching carbohydrate to the gram. The per-meal column is a convenience — spreading protein across meals rather than loading it into dinner is a sensible habit, not a requirement.

To check a label or a recipe app, use the same arithmetic: protein × 4 + carbohydrate × 4 + fat × 9 gets you close to the calories printed. One difference between countries trips people up: US labels include fibre in total carbohydrate, while EU and UK labels list it separately.

These figures are estimates for healthy adults, not medical or dietary advice. If you have kidney disease, diabetes or another condition that affects what you can eat — or you are pregnant — your protein and carbohydrate should be set with a doctor or registered dietitian rather than a calculator.