BMR Calculator - Mifflin-St Jeor Equation

Basal metabolic rate, or BMR, estimates the energy your body uses each day while at rest. That energy supports breathing, circulation, temperature regulation, cell repair, brain activity, and other essential functions. The Mifflin-St Jeor equation uses weight, height, age, and sex to create a practical estimate for generally healthy adults. For men it adds 5 after the shared weight, height, and age terms; for women it subtracts 161. BMR is not the same as the calories used across a normal day. Total daily energy expenditure, or TDEE, applies an activity multiplier to BMR. This calculator provides sedentary, lightly active, moderately active, and very active factors. The categories are broad, and people often overestimate structured exercise or overlook movement at work. Treat the resulting TDEE as a starting hypothesis that can be adjusted using several weeks of consistent intake and body-weight trends. Metabolism varies between individuals. Lean mass, genetics, hormones, sleep, illness, medication, pregnancy, ambient temperature, dieting history, and measurement error can move actual energy use away from an equation. The formula also does not capture every difference associated with body composition. Laboratory indirect calorimetry can measure resting expenditure more directly, but even measured needs change as body weight, activity, and health change. For weight maintenance, estimated TDEE is a reasonable initial calorie target. Weight loss generally requires intake below expenditure, while gain generally requires intake above it, but an aggressive gap may impair nutrition, training, recovery, or wellbeing. Monitor outcomes rather than treating a single estimate as exact. Choose nutrient-dense foods, adequate protein and fibre, and an approach that can be sustained. Anyone under 18, pregnant, breastfeeding, managing diabetes or another medical condition, recovering from an eating disorder, or experiencing unexplained weight change should obtain personalized advice. This calculator is educational and does not prescribe a diet or replace assessment by a registered dietitian or clinician.