Calculators
Macro Calculator
Turn an energy estimate into daily grams of protein, carbohydrate and fat, split across your meals. Results are estimates to plan around, not a prescribed diet.
Estimates for healthy adults aged 19–78, the age range of the study behind the equation. This is general information, not medical or dietetic advice, and it is not meant for pregnancy, breastfeeding, children, eating disorders, diabetes, kidney disease or any condition where diet is part of treatment.
Enter an age from 19 to 78, your height and your weight to see daily macros.
The equation estimates energy use; it does not measure it. The activity multiplier and the goal percentage are assumptions you choose, and body weight usually changes more slowly and less predictably than simple calorie arithmetic suggests. Watch how your weight, energy and training respond over a few weeks and adjust from there, ideally with a registered dietitian. For the energy estimate on its own, use the Calorie Calculator.
Sources: Mifflin et al., 1990 (energy equation); Jäger et al., ISSN position stand, 2017 (protein for exercise); Institute of Medicine Dietary Reference Intakes, 2005 (RDA, AMDR, fibre); NHS fibre guidance.
Your inputs are calculated in your browser and are not uploaded or saved by this tool.
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Frequently asked questions
How does the macro calculator work out my calories?
It uses the Mifflin-St Jeor equation from a 1990 study of 498 healthy adults: 10 × weight in kg + 6.25 × height in cm − 5 × age, then +5 for the male or −161 for the female coefficients. That resting estimate is multiplied by an activity factor from 1.2 to 1.9, and the goal then lowers it by 15% or raises it by 10%. For a 30-year-old man, 175 cm and 70 kg, moderately active, that gives 1,649 kcal resting and 2,556 kcal a day to maintain.
How are calories turned into grams of protein, carbs and fat?
Protein and carbohydrate supply about 4 kcal per gram and fat about 9 kcal per gram. A preset assigns each macro a share of the calorie target, and each share is divided by its energy per gram. In Custom mode protein is set first, fat takes the percentage you choose, and carbohydrate fills whatever calories remain. The per-meal column divides the daily grams evenly by the number of meals.
How much protein do I need?
For most adults the Recommended Dietary Allowance is 0.8 g per kg of body weight a day. The International Society of Sports Nutrition’s 2017 position stand says 1.4–2.0 g/kg a day is sufficient for most people who exercise, and suggests about 0.25 g/kg (roughly 20–40 g) per meal spread every 3–4 hours. The calculator shows your protein in g/kg so you can compare it with both. People with kidney disease should ask their doctor before eating more protein.
Which macro split should I choose?
The balanced preset (50% carbohydrate, 20% protein, 30% fat) sits inside the adult reference ranges of 45–65% carbohydrate, 10–35% protein and 20–35% fat. The higher-protein, low-carb and keto presets move outside some of those ranges on purpose, and the calculator says which. How well you keep to a plan usually matters more than the exact split, so a registered dietitian is the right person to help you pick one for a medical or sports goal.
Is the weight-loss target safe for me?
The calculator cannot know that. A 15% reduction from an estimated daily expenditure is a planning assumption, not a prescription, and the estimate itself can be off for any one person. If the target falls below 1,200 kcal a day the page asks you to speak to a doctor or dietitian first. It is not intended for pregnancy, breastfeeding, children, people with eating disorders, or anyone whose diet is part of medical treatment.
Why is fibre shown separately?
Fibre is part of carbohydrate but mostly is not digested for energy, so the carbohydrate grams here are total carbohydrate. The fibre line uses the Institute of Medicine’s Adequate Intake of 14 g per 1,000 kcal; UK government guidance is 30 g a day for adults. On a keto split the carbohydrate total can be lower than that fibre figure, which shows how hard high fibre is to reach on very low-carb eating.
About this tool
Macronutrients are the three nutrients that supply most of the energy in food: protein, carbohydrate and fat. This macro calculator starts from an energy estimate and divides it into daily grams of each, then splits those grams across 1 to 6 meals. It keeps each step visible — resting estimate, activity multiplier, goal adjustment and split — so you can see which number comes from your body measurements and which comes from a choice you made.
The energy step uses the Mifflin-St Jeor equation, published in the American Journal of Clinical Nutrition in 1990 and derived from adults aged 19 to 78, which is why the age field has that range. Activity multipliers from 1.2 to 1.9 are conventional scenario factors rather than measurements. Imperial inputs are converted to centimetres and kilograms before the equation runs, so both unit systems give the same answer.
Protein can be set by grams per kilogram of body weight, the way most research reports it. The 2017 International Society of Sports Nutrition position stand puts 1.4–2.0 g/kg a day as sufficient for most exercising people, well above the 0.8 g/kg adult RDA, and notes that higher intakes may help resistance-trained people keep lean mass while eating less. The result panel tells you where your protein falls against those figures and flags any macro outside the Institute of Medicine’s adult reference ranges.
Treat the output as a starting point for planning, not as nutrition advice. Real energy needs vary with body composition, health, medicines and how active you really are, and weight changes seldom follow calorie arithmetic exactly. Everything is calculated in your browser and nothing is saved or uploaded. For a personal plan — especially with a medical condition, during pregnancy or when changing weight on purpose — speak to a doctor or registered dietitian.