BMR Calculator

Basal metabolic rate (BMR) is the minimum energy your body needs to sustain vital functions while at complete rest — heart pumping, lungs breathing, brain activity, and cellular repair. It typically accounts for 60–75% of total daily calorie burn in sedentary individuals. The Mifflin-St Jeor equation, validated in 1990, is the most widely used clinical estimate: for men, BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) + 5; for women, the same formula ends with − 161 instead of + 5.

Work through a concrete example: a 30-year-old male, 80 kg, 180 cm. Plug into the formula: BMR = 10(80) + 6.25(180) − 5(30) + 5. That is 800 + 1,125 − 150 + 5 = 1,780 kcal per day. This man burns roughly 1,780 calories even if he stays in bed all day. Any movement, digestion, and exercise add calories on top of this baseline through thermic effect of food and physical activity.

Older formulas like Harris-Benedict (1919, revised 1984) and Katch-McArdle (which uses lean body mass) exist but Mifflin-St Jeor predicts measured resting energy expenditure within about 10% for most healthy adults. Katch-McArdle is more accurate when you know body fat percentage: BMR = 370 + 21.6 × lean mass(kg), where lean mass = weight × (1 − body fat % ÷ 100). If you have body fat data, that formula may refine the estimate.

Factors that raise BMR include greater muscle mass, younger age, taller stature, and male sex (men typically have more lean tissue). Factors that lower it include aging, very low calorie dieting (metabolic adaptation), and loss of muscle during prolonged inactivity. BMR is not destiny — resistance training can increase lean mass and nudge BMR upward over months.

Knowing your BMR is the foundation for setting calorie targets. Multiply BMR by an activity factor to get TDEE (total daily energy expenditure), then adjust for weight goals. This calculator returns your estimated BMR instantly from basic anthropometric data — no lab testing required.