Macro Calculator

How to use the macro calculator

Give the tool your maintenance calories, your body weight and a goal, and it returns a calorie target and the grams of protein, fat and carbohydrate that fill it. Maintenance is total daily energy expenditure, which the tdee-calculator produces from a resting metabolic rate and an activity factor, so if that input is optimistic every number here inherits the optimism.

The goal setting does two things at once: it scales the calorie target, multiplying maintenance by 0.8 to lose fat or 1.1 to build muscle, and it sets the protein figure per kilogram of body weight. Grams are the output that matters. The percentages shown next to them are a result of the calculation, not an input to it.

The order of operations is the entire argument of this tool, so it is worth stating explicitly. Protein comes first, and it comes from body weight rather than from a share of calories, because protein is a requirement rather than a slice of a pie.

The body needs a certain quantity of amino acids to maintain lean tissue, and that quantity is a function of how much body there is and what it is being asked to do, not of how many calories happen to be on the plan this month.

Fat comes second, calculated as a share of the calorie target but with a hard floor of 0.6 g per kilogram of body weight, because fat has structural and endocrine roles that a percentage of a shrinking target can quietly starve. Carbohydrate takes whatever is left.

Read every figure as a starting estimate to be adjusted against what actually happens over several weeks. These are population-derived coefficients applied to a body the tool cannot see: they know nothing about your training history, your medication, your sleep, your digestion or your preferences.

Protein figures around 1.6 g/kg come from resistance-training research on averages, and individuals sit either side of any average. The table below shows the same arithmetic across a range of body weights, maintenance levels and goals, so you can see how the split behaves rather than trusting one row of it.

Why the order matters on a steep cut

Reverse that order and you get the failure this design exists to avoid. Split by three fixed percentages instead, and protein scales with calories, which means it falls exactly when a deficit makes it most necessary.

Take a 100 kg person with a 2,200 kcal maintenance cutting to a 1,760 kcal target. Protein set from body weight at 2.0 g/kg gives 200 g. A thirty percent share of the same 1,760 kcal target gives 528 kcal, which is 132 g, a shortfall of 68 g arriving at the precise moment the body is most likely to draw on lean tissue for energy.

The same target under this tool also triggers the fat floor: a 25 percent share would be 48.9 g, while 0.6 g/kg is 60 g, so the floor wins and carbohydrate is squeezed to 105 g rather than fat being squeezed below a functional level.

The formula, worked line by line

A macro split is three numbers that have to add up to one. The energy densities are the Atwater general factors, established by Wilbur Atwater at the United States Department of Agriculture in the late nineteenth century and still the basis of food labelling: protein and carbohydrate supply 4 kilocalories per gram, fat supplies 9.

Any set of grams therefore implies a calorie total, and any calorie total can be filled by an infinite number of gram combinations. The question a macro calculator answers is which combination, and the answer depends entirely on which of the three you solve for first.

This tool solves in a fixed order: protein, then fat, then carbohydrate. Protein is set as grams per kilogram of body weight. Fat is set as a share of the calorie target, but never below a floor of 0.6 grams per kilogram of body weight.

Carbohydrate is not set at all; it is what remains after the other two have taken their calories. That ordering encodes a claim about which quantities are requirements and which are flexible, and the claim is the reason the tool exists.

target   = maintenance x goalFactor        (0.8 cut, 1.0 maintain, 1.1 gain)
proteinG = proteinPerKg x kg              (2.0 / 1.6 / 1.8 g per kg)
fatG     = max(target x fatPct / 9, 0.6 x kg)
carbKcal = target - proteinG x 4 - fatG x 9
carbG    = carbKcal / 4

The coefficients themselves come from the sports-nutrition literature and carry the uncertainty of any population average. A 2018 systematic review and meta-analysis by Morton and colleagues in the British Journal of Sports Medicine found protein intakes above roughly 1.6 g per kilogram per day produced no further gain in resistance-training adaptations for most participants, which is why maintenance sits there.

Higher intakes during a deficit follow the recommendations set out by Helms and colleagues in the International Journal of Sport Nutrition and Exercise Metabolism in 2014, on the reasoning that protein needs rise as energy availability falls. The fat floor reflects the concern that very low fat intakes are associated with reduced testosterone in men, the subject of a 2021 systematic review and meta-analysis by Whittaker and Wu in the Journal of Steroid Biochemistry and Molecular Biology.

All of it is general information rather than medical or nutritional advice, and a calculator that has seen two numbers about you is not a substitute for a professional who can see the rest.

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