How to calculate your macros (without the influencer math)

Most macro advice online starts from a ratio — 40/30/30, “keto splits,” whatever the algorithm is selling this month. That’s backwards. Macros are derived, not chosen: you set calories from your energy expenditure, set protein and fat from your body weight, and carbs are simply the calories left over. The whole calculation is five steps and one worked example long, and the only numbers you need to memorise are 4 kcal per gram for protein and carbohydrate and 9 kcal per gram for fat.

One caveat up front: this is general education for healthy adults. If you have diabetes, kidney disease, a history of disordered eating, or you’re pregnant, get targets from a physician or registered dietitian instead of a formula.

Step 1: Estimate your TDEE

Everything hangs off total daily energy expenditure — the calories you burn per day. Start with basal metabolic rate from the Mifflin-St Jeor equation (the best-validated of the common predictive formulas, published in 1990 and still the clinical default), then multiply by an activity factor from about 1.2 (sedentary) to 1.7 (very active). Our BMR calculator handles the equation, and our TDEE guide covers the biggest source of error here — people overestimating their activity multiplier.

Worked example: a 30-year-old woman, 70 kg, 168 cm, training three times a week. Mifflin-St Jeor gives a BMR around 1,450 kcal; a moderate activity factor of 1.5 puts TDEE near 2,175 kcal/day. We’ll round to 2,200 and carry her through the rest.

Step 2: Set your calorie target

Adjust TDEE for the goal — as a percentage, not a slogan:

• Fat loss:roughly 10–20% below TDEE. Larger deficits cost more muscle, more hunger, and more rebound; there is no good reason for a healthy person to crash-diet below this range.
• Maintenance: at TDEE, adjusted over a few weeks based on what the scale actually does.
• Muscle gain:roughly 5–15% above TDEE. Muscle is built slowly; calories beyond a modest surplus become fat, not faster gains.

Our example wants fat loss, so a 15% deficit on 2,200 gives a target of about 1,870 kcal/day — call it 1,900.

Step 3: Set protein first

Protein is fixed before anything else because it does the jobs a deficit threatens: preserving lean mass, repairing training damage, and keeping you full. The International Society of Sports Nutrition’s position stand recommends about 1.4–2.0 g per kg of body weight per day for exercising people — well above the sedentary RDA of 0.8 g/kg, and deliberately so. While dieting, the higher end of that range earns its keep.

Our example, at 70 kg and cutting, picks 1.8 g/kg: 126 g of protein, which costs 126 × 4 = 504 kcal.

Two myths worth defusing here. First, more is not endlessly better — above roughly 2.0–2.2 g/kg the extra protein mostly displaces carbs and fat you’d rather have. Second, the “your body can only absorb 30 g per meal” claim confuses absorption (essentially complete) with per-meal muscle-protein synthesis (which does plateau). Spreading protein over 3–5 meals is a good idea; fearing a 50 g dinner is not.

Step 4: Set a fat minimum

Dietary fat isn’t a leftover — it carries essential fatty acids and fat-soluble vitamins and supports hormone production. The Institute of Medicine’s reference range puts fat at 20–35% of total calories; a practical floor is around 0.5 g per kg of body weight, and chronically dipping below ~20% of calories is where problems start. Within the range, placement is preference: people who like fattier foods take more here and fewer carbs, and vice versa.

Our example sets fat at 25% of 1,900 kcal = 475 kcal, and 475 ÷ 9 ≈ 53 g of fat — comfortably above her 35 g floor.

Step 5: Carbs are the remainder

Carbohydrate is the flexible macro precisely because it has no hard biological minimum the way protein and essential fats do — which is why it’s calculated last, by subtraction:

carbs (g) = (calories − protein g × 4 − fat g × 9) ÷ 4

For our example: 1,900 − 504 − 477 = 919 kcal remaining, and 919 ÷ 4 ≈ 230 g of carbs. Her finished targets: 1,900 kcal, 126 g protein, 53 g fat, 230 g carbs. Someone who trains hard would keep carbs high like this; someone sedentary or simply carb-indifferent could shift 20–30 g of the remainder into fat with no effect on results. That flexibility is the point — the “perfect ratio” framing gets it exactly wrong.

Adjusting for cutting, maintaining, and bulking

The procedure never changes; only steps 2 and 3 shift. Cutting: 10–20% deficit, protein toward 1.8–2.0 g/kg, fat near its floor if you want the carbs for training. Maintenance: calories at TDEE, protein anywhere in 1.4–2.0 g/kg. Bulking: 5–15% surplus, protein around 1.6–2.0 g/kg, most of the surplus going to carbs. In every case, the numbers are opening bids: watch two to three weeks of scale trend (and how training feels), then adjust calories by 5–10% rather than rebuilding from scratch.

The tracking-error reality check

Before you chase your targets to the gram, know what you’re measuring with. Nutrition labels are permitted substantial rounding and tolerance under labelling regulations — a “200-calorie” serving can legally deviate by a meaningful margin. Portion estimation adds more error: studies of self-reported intake consistently find people under-report, often by 20% or more. Restaurant meals are guesses on top of guesses. The practical conclusion isn’t to give up on tracking — it’s to treat your macros as a weekly average with a tolerance of ±5–10 g per macro, and to judge the plan by outcomes (weight trend, gym performance, hunger) rather than by log-perfection. Pairing intake with an estimate of output from a calories-burned calculator is useful for the same reason: both sides of the ledger are estimates, and trends beat snapshots.

Short version: TDEE, then calories, then protein (1.4–2.0 g/kg if you train), then a fat floor, then carbs by subtraction at 4/4/9 kcal per gram. Run it once, live with the numbers for a few weeks, and adjust from results — and if a medical condition is in the picture, run the numbers past a professional before running them past your kitchen.