BMR (Basal Metabolic Rate)

BMR is the energy the body spends doing nothing at all — breathing, circulating blood, holding temperature. It is the floor that every other daily calorie number is built on top of, and the largest single share of most people's expenditure.

BMR (Basal Metabolic Rate) is the energy the body spends doing nothing at all: breathing, circulating blood, running the brain, holding its own temperature. Lying still in a dark room for 24 hours still costs this much.

BMR is not the same number as TDEE, and confusing the two is the most common way a calorie target ends up hundreds of calories wrong. BMR is the floor. TDEE is that floor plus everything the day added on top — walking, fidgeting, standing, digesting (NEAT) and deliberate exercise. Eating at BMR when the day contained a commute and a leg session is not a small deficit; it is a large one.

Every BMR figure a calculator gives, including the one on Cookrange’s calorie calculator, is a population estimate rather than a measurement. The calculator uses the Mifflin-St Jeor equation — height, weight, age and sex — which is the same formula the app itself runs. Measuring a real BMR requires indirect calorimetry in a lab, and two people matching on all four inputs can still differ.

That gap is why the estimate is a starting point and not a verdict. It gets useful once several weeks of logged intake and weight sit next to it, because at that point the trend corrects the formula. BMR also moves: sustained under-eating lowers it, which is one of the mechanisms behind metabolic adaptation.