BMR Calculator

Understanding Basal Metabolic Rate

Your Basal Metabolic Rate (BMR) is the number of calories your body requires each day simply to maintain life when at complete rest. These calories fuel involuntary processes such as breathing, pumping blood, regulating body temperature, producing hormones, and repairing cells. BMR typically accounts for 60 to 70 percent of the calories you burn in a day, making it the single largest component of your total energy expenditure.

This calculator offers two well-established formulas. The Mifflin-St Jeor equation, published in 1990, is considered the most accurate for modern populations and is recommended by the American Dietetic Association. For men it calculates BMR as 10 times weight in kilograms plus 6.25 times height in centimeters minus 5 times age plus 5. For women, the constant changes to minus 161. The Harris-Benedict equation, originally developed in 1919 and revised in 1984, uses slightly different coefficients and tends to produce higher estimates, especially in overweight individuals.

Knowing your BMR is the foundation for any nutrition plan. By itself, BMR tells you the bare minimum calories your body needs. To determine how many calories you actually need each day, multiply your BMR by an activity factor to get your Total Daily Energy Expenditure (TDEE). Several factors influence your BMR beyond the inputs used in these formulas. Lean muscle mass is the biggest driver, because muscle tissue is metabolically active and burns calories even at rest. This is why resistance training is so effective at raising BMR over time. Age, genetics, hormonal balance, sleep quality, and even ambient temperature also play roles. Avoid crash diets that fall well below your BMR, as they can trigger metabolic adaptation and make long-term weight management harder.