Macro calculator for weight loss

Two questions, in order

Macro calculators tend to blur two separate problems into one answer. They are not the same problem and they do not have the same quality of evidence behind them.

1. How many calories? Your resting metabolism from the Mifflin-St Jeor equation, multiplied by an activity level, minus the deficit you choose. That number is what the energy-balance model actually responds to, and the projection on this page is the same Hall dynamic model that drives our timeline calculator, so the two pages cannot contradict each other.
2. How do those calories split? Percentages into grams, using the Atwater factors. This is arithmetic. What is not arithmetic is which split you should pick, and that is where most calculators quietly assert a preference as though it were a finding.

The only published ranges

The Institute of Medicine’s Dietary Reference Intakes set Acceptable Macronutrient Distribution Ranges for adults aged 19 and over: carbohydrate 45 to 65% of energy, total fat 20 to 35%, and protein 10 to 35%. They also set an RDA of 0.80 g of protein per kg of body weight per day, and 130 g of carbohydrate a day, the latter based on the brain’s glucose requirement.

Those figures were derived for chronic-disease risk in a general, weight-stable population. They are not a fat-loss prescription, and this site does not pretend they are. What they are is the only macronutrient ranges anyone can point at a document for — so the calculator checks your split against them and marks anything outside, in either direction.

Protein: what we could not source

The RDA of 0.80 g/kg/day is well documented and is the floor for a healthy adult. It is also, almost certainly, not the right target for somebody deliberately eating less: the reason to raise protein during weight loss is to protect lean tissue, and the RDA was never derived for that situation.

We could not trace a specific higher figure to a primary guideline document, so we do not publish one. Numbers like 1.2, 1.6 or 2.0 g/kg circulate constantly, and you will find calculators that state them as though the National Academies had signed them. They have not. The calculator above shows your protein in g/kg next to the RDA so you can see where you sit, and stops there.

The same discipline applies across this site: where the evidence stops, the page says so instead of filling the gap. Read the full methodology.

Why the grams are approximate even when the maths is exact

The 4/4/9 factors are general factors permitted by US labelling regulation, and the same regulation offers alternative sets — specific Atwater factors for particular foods, and modified factors that subtract non-digestible carbohydrate and charge soluble fibre at 2 calories a gram. Which set a manufacturer used is not printed on the packet.

So your gram targets are exact arithmetic on an input that carries a few per cent of slop before you have weighed anything. That is fine. It is a reason to treat the targets as targets rather than as a budget to the gram.

Next

• Weight loss timeline calculator — what the deficit does over real calendar dates.
• Weight loss percentage calculator — scoring progress the way the trials do.
• Walking calorie calculator — the other side of the energy balance.