Macros

Set the calories first, then the macros

Macros do not decide whether you lose weight — the calorie total does. What the split decides is how much muscle you keep while it happens, how full you feel, and whether you can train. So the order matters: find the target with thedeficit calculator, then divide it here. If you arrive from that page the number is carried across for you.

Why protein comes from your weight, not a percentage

Almost every macro calculator sets protein as a share of calories, and that breaks in the one place it matters most. At 1,200 kcal, 30% is 90 g of protein — for an 80 kg person in a deficit that is far too little, precisely when the risk of losing lean tissue is highest. Protein need scales with the body you are trying to keep, not with the energy you happen to be eating.

So this page fixes protein in grams per kilogram first. The default is 1.6 g/kg, which is where the benefit for muscle retention flattens off in the meta-analyses. Training hard in a deficit, higher is reasonable — theprotein calculator has the full range and the sources behind it.

Fat next, and the floor underneath it

Fat is set as a share of energy — 20% to 35% is the accepted range, and this page starts at 25%. Below 20% there is no benefit, and there is a real cost: fat is how you absorb vitamins A, D, E and K, and it carries the two fatty acids your body cannot make. The page flags it when your split drops under the greater of 20% of calories or 0.5 g per kilogram.

Carbohydrate takes the remainder

Whatever energy is left after protein and fat goes to carbohydrate. That makes it the flexible one, which is the right way round — it is the macro that fuels hard training and the one most easily cut when it suits you. The adult reference intake is 130 g a day, based on what the brain uses; eating below it is a choice people make deliberately, so this page flags it rather than refusing.

What 40/30/30 and 40/40/20 actually are

They are percentages someone picked, repeated until they sounded official. The awkward part is that sites do not even agree on the order — the same "40/30/30" is published as carb-led on one page and protein-led on another. None of them is wrong exactly, but none is derived from anything either. A split built from grams per kilogram at least tells you where each number came from.

Where this stops applying

These are population ranges for healthy adults. Chronic kidney disease usually means a protein restriction set by a clinical team, not a multiplier off a web page. If you take insulin or a sulfonylurea, changing carbohydrate intake changes your dosing and needs to be planned with whoever prescribes it. Pregnancy, breastfeeding and under-18s all have different requirements. And grams multiplied back by 4, 4 and 9 will not re-sum exactly to your target — rounding, not an error.