What Is Basal Metabolic Rate?
BMR is the minimum number of calories your body needs to perform basic life-sustaining functions — breathing, circulation, nutrient processing, and cell production. It accounts for 60-75% of total daily calorie expenditure for most people.
Mifflin-St Jeor Equation
Published in 1990, the Mifflin-St Jeor equation is considered the most accurate BMR formula for the general population:
- Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
Activity Level Multipliers
| Activity Level | Description | Factor |
|---|---|---|
| Sedentary | Little or no exercise | BMR × 1.2 |
| Light | Exercise 1-3 times/week | BMR × 1.375 |
| Moderate | Exercise 4-5 times/week | BMR × 1.465 |
| Active | Daily exercise or intense 3-4 times/week | BMR × 1.55 |
| Very Active | Intense exercise 6-7 times/week | BMR × 1.725 |
| Extra Active | Very intense daily exercise or physical job | BMR × 1.9 |
Factors That Affect BMR
- Muscle mass: More muscle = higher BMR. Resistance training is the best way to boost metabolism
- Age: BMR decreases ~1-2% per decade after age 20 due to muscle loss
- Gender: Men typically have higher BMR due to greater muscle mass and larger body size
- Body size: Larger bodies require more energy to maintain basic functions
- Genetics: Metabolic rate varies up to 15% between individuals of similar size and composition
- Hormones: Thyroid hormones (T3, T4) directly regulate metabolic rate. Hypothyroidism can lower BMR by 20-40%
BMR vs Other Calorie Measures
- BMR: Calories at complete rest (lying still, fasting, thermoneutral environment)
- RMR (Resting Metabolic Rate): Similar to BMR but measured under less strict conditions. Usually 10-20% higher than BMR
- TDEE: Total calories burned in a day including all activity. Use our TDEE Calculator for detailed planning
For a complete fitness profile, combine BMR with our Body Fat Calculator and Macro Calculator.