Macro calculator

Step 1 - kcal target. BMR uses Mifflin-St Jeor; activity multiplier turns BMR into TDEE; then ±deficit/surplus per goal. You can also override the kcal target if you already have one from your own data.

BMR_male   = 10·W + 6.25·H - 5·A + 5
BMR_female = 10·W + 6.25·H - 5·A - 161
TDEE       = BMR × activity multiplier
kcal target = TDEE - 500 (lose) / TDEE (maintain) / TDEE + 250 (build)

Step 2 - protein first. Set from the same lookup table the protein calculator uses: 1.6-2.2 g/kg for lifters, 1.2-1.4 for active non-lifters, lower for sedentary. Convert at 4 kcal/g.

protein_g    = bodyweight_kg × g_per_kg
protein_kcal = protein_g × 4

Step 3 - fat with a floor. 20-30% of total kcal is the standard range. The floor (~0.6-1.0 g/kg) exists because too little dietary fat suppresses testosterone and other steroid hormones, especially during a cut. Convert at 9 kcal/g.

fat_kcal = clamp(kcal_target × 0.25, fat_floor_kcal, kcal_target × 0.30)
fat_g    = fat_kcal / 9
fat_floor_g = bodyweight_kg × 0.8

Step 4 - carbs fill the rest. Whatever kcal remain after protein and fat become carbs at 4 kcal/g. This is why we don't fix carbs first: in a cut, deeper cuts reduce carbs (the only macro both abundant in the diet and not strictly required for body composition).

carb_kcal = kcal_target - protein_kcal - fat_kcal
carb_g    = carb_kcal / 4

Caveat: these are starting points. If you lose performance, sleep, or libido, raise fat first, then carbs. If you stall, the kcal target is what to adjust, not the split.