What Is BMR and Why It Matters for Your Health
Your BMR determines how many calories you burn at rest. Learn what influences it and how to use it for better health decisions.
Use the BMR Calculator
Calculate your Basal Metabolic Rate
BMR Defined
Basal Metabolic Rate, commonly abbreviated as BMR, is the number of calories your body burns while at complete rest just to keep you alive. This includes the energy needed for breathing, circulating blood, maintaining body temperature, growing and repairing cells, and keeping your organs functioning. For most people, BMR accounts for somewhere between 60 and 75 percent of total daily calorie expenditure. That means the majority of the calories you burn each day have nothing to do with exercise or physical activity. They are spent simply on the biological processes that keep your body running around the clock.
Factors That Affect BMR
Several factors influence your BMR, and most of them are things you cannot control.
BMR vs TDEE
BMR represents only your resting calorie needs. Your Total Daily Energy Expenditure, or TDEE, adds the calories burned through physical activity, digestion (called the thermic effect of food), and non-exercise activity like fidgeting and walking around during the day.
How to Use Your BMR
Knowing your BMR gives you a useful baseline for nutritional planning. The most important practical application is that your BMR represents a calorie floor: eating below your BMR for extended periods can trigger metabolic adaptation, where your body slows down its metabolism to conserve energy. This can lead to muscle loss, fatigue, hormonal disruption, and a frustrating plateau in weight loss efforts. For sustainable weight loss, nutrition experts generally recommend creating a moderate calorie deficit from your TDEE, not from your BMR. For weight maintenance, eating at your TDEE level is the target. For muscle gain, eating slightly above TDEE while prioritizing protein intake supports growth without excessive fat accumulation.
Common BMR Calculation Methods
The two most widely used formulas for estimating BMR are the Mifflin-St Jeor equation and the Harris-Benedict equation. The Mifflin-St Jeor equation, published in 1990, is considered more accurate for most people and is the one recommended by the Academy of Nutrition and Dietetics. It calculates BMR based on weight in kilograms, height in centimeters, age, and sex. The Harris-Benedict equation, first published in 1919 and revised in 1984, uses the same inputs but produces slightly different results. Both are estimates, and individual variation means your actual BMR could differ by 5 to 10 percent from the calculated value. The most accurate way to measure BMR is through indirect calorimetry in a clinical setting, but the formulas are good enough for practical planning.