BMR and calorie needs calculator

Basal metabolic rate is the energy your body uses in a state of complete rest — breathing, circulating blood, maintaining body temperature, and every other function that keeps you alive, before you've moved a muscle or digested a meal. It typically accounts for 60–75% of the calories most people burn in a day, which is why it's the starting point for working out total daily calorie needs rather than a small side detail.

This calculator uses the Mifflin-St Jeor equation: for men, BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5; for women, the same calculation but −161 instead of +5. Published in 1990, it's the equation most modern nutrition and clinical guidelines recommend over the older Harris-Benedict formula (1919, revised 1984), since it was derived from a more representative and up-to-date population and has been shown in later validation studies to more closely predict measured resting energy expenditure across a wider range of body types.

BMR alone only tells you the calories you'd burn lying still all day. Total daily energy expenditure (TDEE) multiplies BMR by an activity factor — from 1.2 for a sedentary lifestyle up to 1.9 for very hard training or a physically demanding job — to estimate real-world daily calorie needs. The "lose" and "gain" targets above apply a roughly 550 kcal/day deficit or surplus to that TDEE figure, based on the widely used approximation that a kilogram of body fat represents about 7,700 kcal — a rate of change of around 0.5 kg (1lb) a week.

The Mifflin-St Jeor equation is a population-average formula — it doesn't know your muscle mass, body composition, genetics, hormone levels, or any medical conditions that affect metabolism, all of which can shift an individual's real BMR meaningfully above or below the estimate. Treat the figures here as a sensible starting point for planning, not an exact measurement — the only way to know your true BMR is direct measurement (indirect calorimetry) in a clinical or lab setting.