Macro calculator

How the numbers are built

The calculation runs in three stages. Mifflin-St Jeor estimates basal metabolic rate — what you would burn at complete rest. An activity multiplier converts that to total daily energy expenditure. Then a percentage adjustment sets the target above or below maintenance depending on the goal.

Each stage adds uncertainty. Mifflin-St Jeor is the best-validated of the common equations but still lands within 10% of measured BMR only about 80% of the time. The activity multiplier is the largest source of error, because self-reported activity is notoriously optimistic and the bands are wide.

Treat the output as a starting point. Eat at the target for two to three weeks, track weight, and adjust based on what actually happens. Real data about you beats any equation.

Protein

Research on protein and body composition consistently supports intakes well above the minimum RDA when training or in a calorie deficit — commonly 1.6 to 2.2 g per kilogram of body weight. Above roughly 2.2 g/kg the additional benefit becomes hard to detect in studies.

Protein does two useful things in a deficit: it helps preserve lean mass that would otherwise be lost alongside fat, and it is the most satiating of the three macronutrients per calorie. It also has the highest thermic effect — roughly 20-30% of its energy is used in digestion, against 5-10% for carbohydrate and 0-3% for fat.

Fat and carbohydrate

Dietary fat has a floor. It is required for hormone production and for absorbing vitamins A, D, E and K, and intakes below about 20% of calories are associated with problems over time. Above that floor, the fat-to-carbohydrate ratio is largely a preference question.

Well-controlled studies matching calories and protein find little difference in fat loss between higher-carb and lower-carb approaches. What differs is adherence, and adherence is personal. If you train hard and feel flat on low carbohydrate, that is a real signal. If lower carbohydrate keeps you full and you stick to it, that is equally real.

Rate of change

A deficit of around 20% below maintenance produces steady fat loss for most people without the fatigue, hunger and lean-mass loss that come with aggressive restriction. Larger deficits do not reliably produce proportionally better results — they produce worse adherence and more muscle loss.

For gaining, a surplus of about 10% is enough to support muscle growth. Bigger surpluses add fat faster than they add muscle, because the rate at which muscle can be built is limited by training and recovery rather than by available calories.

The calculator will not display a target below 1,500 kcal for men or 1,200 for women. Sustained intakes below those levels make it difficult to meet micronutrient needs and should be supervised by a doctor or registered dietitian rather than set by a web page.

Common questions