BMR Calculator

Basal metabolic rate is what your body burns in 24 hours doing nothing at all — no food, no movement. It is not what you should eat: multiply it by an activity factor first. Mifflin-St Jeor suits most people; pick Katch-McArdle only if your body fat percentage was properly measured.

Your basal metabolic rate is the energy your body spends doing nothing at all — breathing, circulating blood, repairing cells, holding its temperature — counted in kilocalories over twenty-four hours of complete rest. In someone with a desk job it accounts for roughly 60 to 75 percent of everything burned in a day. The calculator offers three published equations, and they are genuinely different equations rather than variants of one. Mifflin-St Jeor is the default and the best validated: a 2005 review in the Journal of the American Dietetic Association found it predicts resting energy expenditure within ten percent for about 82 percent of non-obese people, the best of the four common formulas. The revised Harris-Benedict equation, recalibrated by Roza and Shizgal in 1984, usually returns a slightly higher figure and is still asked for in clinical settings. Katch-McArdle takes a different route: it works from lean body mass and ignores sex entirely, which makes it the most accurate option — but only if you actually have a measured body fat percentage. The caveat that matters most is that this is not a calorie target. Your basal rate is the floor your body needs at rest, not a plan for what to eat. Eating at or below it is severe restriction, and the usual consequences are muscle loss, hormonal disruption and metabolic adaptation.