Macro Calculator

Working out your daily protein, carb, and fat targets requires deciding on a calorie goal, then splitting it into ratios that depend on your training and goals — and the answers are scattered across nutrition forums.

This calculator takes age, sex, height, weight, activity level, and goal (cut, maintain, bulk) and returns total daily calories using Mifflin-St Jeor (the most accurate of the common BMR formulas). Then it splits calories into macros: protein based on body weight (roughly 0.8–1g per pound for active people), fat based on a percentage floor (0.3g per pound minimum), and carbs filling the remainder.

The macro split that comes out is a starting point, not gospel. Endurance athletes typically need higher carbs; strength athletes higher protein; ketogenic diets reverse the usual fat/carb split entirely. Adjust the macro percentages if your training goals lean to one of those extremes.

Mifflin-St Jeor calculates basal metabolic rate (BMR) — the calories your body burns at complete rest. For men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161. The activity multiplier converts BMR to TDEE (total daily energy expenditure): 1.2 sedentary, 1.375 light activity, 1.55 moderate, 1.725 very active, 1.9 athletic. Cut subtracts ~500 calories/day (1 lb/week), bulk adds 200-500 depending on aggression.

The pain this addresses: macro tracking sounds simple until you realize protein, carb, and fat targets all need to come from somewhere principled. Pulling them off Reddit gives you ten different formulas with no way to choose. The calculator picks defensible defaults (protein 0.8-1g/lb for active people, fat 0.3g/lb minimum, carbs filling remainder), explains why, and lets you adjust if you have specific goals. The defaults are 'good enough for 90% of cases' — not optimized for elite performance, just rational for general use.

Worked example: 30-year-old female, 170cm, 65kg, moderate activity, maintenance goal. BMR: 10×65 + 6.25×170 − 5×30 − 161 = 650 + 1062.5 − 150 − 161 = 1401.5. TDEE: 1401.5 × 1.55 = 2172. Macros: protein 65×1g/lb...wait, that's 65kg = 143lb, so 143g protein = 572 calories. Fat at 0.35g/lb = 50g = 450 calories. Carbs filling: 2172 − 572 − 450 = 1150 calories = 287g carbs. The split (~26% protein, 21% fat, 53% carbs) is pretty typical for someone whose training mixes endurance and strength.

Where this is approximate: activity multipliers are guesses. People consistently overestimate their activity level — 'I work out 4 times a week' is often called moderate when it's actually closer to light. If your weight isn't tracking with the calculator's prediction after 2-3 weeks, the activity assumption is the most likely culprit. Drop down one level and recalculate. Real bodies vary by ±10% from formula predictions due to NEAT (non-exercise activity thermogenesis) differences and metabolic individuality. The calculator gets you to a starting point; actual outcomes are what calibrate it.