Basal Metabolic Rate (BMR): How to Calculate It and What to Use It For

Basal metabolic rate (BMR) is the amount of energy your body would use if you were at complete rest for 24 hours. This energy fuels brain function, heartbeat, breathing, cell regeneration, and all processes necessary for survival. BMR is the foundation of individual calorie needs, to which you must add calories burned through daily activity. For an average adult, this ranges from 1200-1800 calories daily, but it heavily depends on body composition. Knowing your basal metabolic rate helps you set realistic fat loss or muscle building goals.

The most commonly used calculation method is the Harris-Benedict formula, which considers gender, age, weight, and height. For men: 88.362 + (13.397 × weight kg) + (4.799 × height cm) - (5.677 × age). For women: 447.593 + (9.247 × weight kg) + (3.098 × height cm) - (4.330 × age). The Mifflin-St Jeor formula usually gives more accurate results for modern lifestyles: for men (10 × weight kg) + (6.25 × height cm) - (5 × age) + 5, for women the same minus 161. Online calculators simplify the math, but body composition measurement is the most accurate method.

BMR only shows calories burned at rest, while TDEE (Total Daily Energy Expenditure) is total daily calorie expenditure. You get TDEE by multiplying your BMR by an activity multiplier: 1.2 for sedentary lifestyle, 1.375 for light activity, 1.55 for moderate activity. Those doing intense workouts multiply by 1.725, and extremely active individuals by 1.9. TDEE is the number from which you subtract calories for fat loss or add calories for muscle building. The GetFIT App automatically calculates both values and adjusts them to your activity level.

During fat loss, your body adapts to lower calorie intake and reduces energy expenditure as a survival instinct. Lower body weight automatically means lower BMR because there's less tissue to maintain. If we lose weight too quickly or eat too few calories, the body breaks down muscle tissue as well, further decreasing metabolic rate. Hormonal changes, especially decreased thyroid hormones, can also slow metabolism. That's why a protein-rich diet and strength training are important to preserve muscle mass during a diet.

Building muscle mass is the most effective way to raise BMR, since muscle tissue requires more energy to maintain than fat tissue. Regular strength training can increase basal metabolic rate by 5-10% long term. Adequate protein intake is also important because protein digestion requires more calories than other nutrients. HIIT workouts temporarily speed up metabolism even after the workout, for up to 24 hours. Avoid extreme calorie deficits and rapid weight loss because these slow metabolism, making long-term weight loss more difficult.