BMRBasal Metabolic Rate

BMR (Basal Metabolic Rate) is the energy your body uses at complete rest to maintain vital functions — breathing, circulation, cell repair and organ function. It is the largest single component of most people's daily energy use.

It matters because it forms the base of your TDEE and explains why larger and more muscular people burn more calories at rest. Crash dieting can lower it, which is one reason very aggressive cuts backfire.

In practice, BMR is estimated from equations such as Mifflin–St Jeor using your age, sex, height and weight.