What Is BMR?
Basal Metabolic Rate is the number of calories your body burns at complete rest just to keep essential functions running — breathing, circulation, cell production, brain activity. It typically accounts for 60-75% of total daily calorie burn, making it the single largest component of daily energy expenditure for most people.
BMR vs. TDEE
BMR is calories burned at rest; Total Daily Energy Expenditure (TDEE) adds in calories burned through daily movement and exercise on top of BMR. TDEE is the more useful number for weight management, since it reflects actual daily calorie burn rather than a resting baseline.
Which Formula Is More Accurate?
The Mifflin-St Jeor equation, published in 1990, is generally regarded by dietitians as more accurate for the modern population than the older Harris-Benedict equation, which was based on data from 1919 and tends to slightly overestimate BMR for people with lower body fat percentages. Both formulas use weight, height, age, and sex, since these are the strongest predictors of resting metabolism available without specialized equipment.
Why Muscle Mass Matters More Than These Formulas Show
Muscle tissue burns more calories at rest than fat tissue, which is why two people of the same weight and height can have meaningfully different BMRs depending on body composition. Formulas based on weight and height alone can't fully capture this — a more precise measurement requires methods like DEXA scans or indirect calorimetry, which estimate lean body mass directly.
Using BMR for Weight Goals
To lose weight, most guidance suggests eating below TDEE (not BMR) by a moderate deficit — commonly 500 calories/day for roughly 1 lb (0.45 kg) of loss per week. Eating below BMR itself is generally discouraged, since it can signal the body to conserve energy by slowing metabolism, and it's harder to sustain nutritionally over time.