Macro Calculator

Background.

Counting macros means tracking where your calories come from, not just how many there are: grams of protein, fat and carbohydrate each day. A target takes two steps, and both happen on this page. First you need an estimate of the energy you burn in a day; then that total is shared out among the three macronutrients in proportions you pick.

The energy estimate starts with the Mifflin-St Jeor equation, published in 1990, which predicts resting energy expenditure from weight, height, age and sex. Multiplying it by an activity factor gives maintenance calories, roughly what you would eat to hold your weight steady. The factor is 1.2 for a mostly seated day, and 1.55 is the figure conventionally used for moderate exercise three to five days a week.

Sharing out is where units start to matter. Protein and carbohydrate supply about 4 kcal per gram and fat about 9, so the same 30% of calories buys fewer than half as many grams of fat as of protein. You set the protein and fat percentages; carbohydrate takes whatever is left.

Because percentages scale with total calories, they can hide big numbers. A 30% protein share sounds moderate, yet for a moderately active 80 kg man it comes to about 204 g a day, 2.55 g for every kilogram of body weight and more than three times the 0.8 g/kg recommended dietary allowance for adults. If you think about protein per kilogram, check the gram figure, not the percentage.

The targets are for maintenance. No deficit for weight loss or surplus for gaining is applied, alcohol is not counted, and fibre is treated like any other carbohydrate even though it yields less energy. Conditions such as kidney disease or diabetes change what a sensible split looks like, and that is a conversation for a doctor or dietitian.

What is macro calculator?

Macronutrients are the three nutrients that supply most of the energy in food: protein, fat and carbohydrate. A macro target expresses a daily calorie budget as grams of each, using the standard energy values of 4 kcal per gram for protein and carbohydrate and 9 kcal per gram for fat. Here the budget is maintenance energy, the Mifflin-St Jeor resting estimate multiplied by an activity factor, and the carbohydrate target is whatever is left once the protein and fat shares are taken out.

How to use this calculator.

1. 01Choose the male or female constant, then enter your age (18 to 100), height in centimetres and weight in kilograms. The sex setting changes only one constant in the resting-energy equation: +5 for male, −161 for female.
2. 02Enter an activity factor: 1.2 if you mostly sit, 1.375 for light exercise one to three days a week, 1.55 for moderate exercise three to five days, 1.725 for hard exercise six or seven days. If in doubt, take the lower value, because the factor multiplies everything else.
3. 03Enter the share of calories you want from protein and from fat. Together they cannot exceed 100%; carbohydrate receives the remainder automatically.
4. 04Read maintenance calories and the three gram targets. Divide the protein grams by your weight to see what the percentage means per kilogram, and adjust the split if that looks too high or too low.

The formula.

Resting energy (kcal/day) = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + s, where s is +5 with the male constant and −161 with the female one. Maintenance calories = resting energy × activity factor. Protein grams = maintenance × protein% ÷ 4; fat grams = maintenance × fat% ÷ 9; carbohydrate grams = (maintenance − protein calories − fat calories) ÷ 4. Weight carries the largest coefficient: each extra kilogram adds 10 kcal of resting energy, or 15.5 kcal of maintenance at a 1.55 factor, and each extra year takes 5 away. The activity factor scales the whole answer, so moving from 1.55 to 1.725 raises maintenance by about 11%, typically a bigger shift than any likely error in height or age. The divisors 4, 9 and 4 are the Atwater energy factors.

A worked example.

Frequently asked questions.

References& sources.

1. [1]Mifflin et al.. American Journal of Clinical Nutrition 1990. Resting energy expenditure prediction equation. Retrieved 2026-08-06.
2. [2]U.S. National Institutes of Health. Health information current 2026. Evidence-based health measurement context. Retrieved 2026-08-06.
3. [3]U.S. National Library of Medicine. PubMed record current 2026-08-06. Indexed derivation and validation literature. Retrieved 2026-08-06.