BMR Calculator
Calculate your Basal Metabolic Rate — the calories your body burns at complete rest. Compared across three leading formulas for maximum accuracy.
What BMR Actually Means
BMR is the number of calories your body burns doing absolutely nothing — in a temperature-controlled room, lying still, 12+ hours after your last meal. It accounts for approximately 60–75% of total daily energy expenditure for sedentary people. Breathing, heartbeat, brain activity, cell repair, and organ function all consume this energy continuously.
Mifflin-St Jeor vs Harris-Benedict
Mifflin-St Jeor (1990): Male: (10×weight) + (6.25×height) − (5×age) + 5. Female: same minus 161. This is considered the most accurate for most people in studies comparing to measured metabolic rate. Harris-Benedict (revised 1984) tends to overestimate by 5% on average, particularly for sedentary individuals.
BMR Is Not TDEE
BMR is the foundation — to get your Total Daily Energy Expenditure (TDEE), multiply BMR by an activity multiplier (1.2 for sedentary to 1.9 for very active). Eating at BMR level would put most people in a significant deficit. Use the TDEE calculator for your actual calorie needs.
What Affects BMR
Muscle mass increases BMR — each kilogram of muscle burns approximately 13 kcal/day at rest. Age decreases BMR by roughly 1–2% per decade after 30, partly because of muscle loss. Fasting, very low calorie diets, and extreme weight loss can reduce BMR by 15–40% through adaptive thermogenesis — the metabolic adaptation studied in post-diet 'rebound' research.
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