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About This Calculator
Basal Metabolic Rate represents the number of calories your body burns at complete rest just to maintain vital functions like breathing, circulation, and cell production. This calculator uses the Mifflin-St Jeor or Harris-Benedict equation with your age, sex, height, and weight to estimate your BMR. Knowing your baseline metabolic rate is essential for designing accurate meal plans and understanding your energy needs.
Quick Tips
- 1 Recalculate your BMR every 10 pounds of weight change for accuracy.
- 2 Your BMR decreases with age, so adjust calorie intake accordingly.
- 3 Building muscle mass increases your BMR even at rest.
Example Calculation
A 40-year-old male, 180 lbs (81.6 kg), 5'11" (180 cm), Mifflin-St Jeor equation.
BMR: 1,759 calories/day | 73 cal/hour at rest | Minimum daily intake baseline
What is Basal Metabolic Rate?
Basal Metabolic Rate (BMR) is the number of calories your body needs to perform basic life-sustaining functions at complete rest. These functions include breathing, circulation, cell production, nutrient processing, and temperature regulation. BMR typically accounts for 60-75% of your total daily calorie expenditure.
Mifflin-St Jeor vs Harris-Benedict
The Mifflin-St Jeor equation (1990) is considered the most accurate for most people, using the formula: Men: 10 × weight(kg) + 6.25 × height(cm) - 5 × age - 161; Women: same but subtract 161 instead of adding 5. The Harris-Benedict equation (1919, revised 1984) is older but still widely used and may be slightly more accurate for very active or obese individuals.
Factors That Affect BMR
Several factors influence BMR beyond age, sex, and body size. Muscle mass is the biggest controllable factor — more muscle means higher BMR. Genetics play a role in natural metabolic rate. Hormones, particularly thyroid hormones, significantly impact metabolism. Environmental temperature, certain medications, and even caffeine can temporarily alter BMR.
Using BMR for Fitness Goals
Knowing your BMR is the foundation for any diet or fitness plan. Multiply your BMR by an activity factor (1.2 for sedentary to 1.9 for very active) to estimate Total Daily Energy Expenditure. From there, create a calorie surplus or deficit based on whether you want to gain muscle or lose fat. Never eat fewer calories than your BMR for extended periods.
Frequently Asked Questions
The Mifflin-St Jeor equation is considered the most accurate predictive equation for BMR in most adults, according to the American Dietetic Association. It was developed in 1990 using modern data and tends to be within 10% of measured values.
The most effective way to increase BMR is building lean muscle mass through resistance training, as muscle tissue burns more calories at rest than fat tissue. Eating adequate protein, staying hydrated, and getting enough sleep also support a healthy metabolic rate.
BMR and Resting Metabolic Rate (RMR) are similar but not identical. BMR is measured under strict conditions (complete rest, fasted state, thermoneutral environment). RMR is measured under less restrictive conditions and is typically 10-20% higher than BMR.
BMR decreases with age primarily because of the natural loss of muscle mass (sarcopenia), which begins around age 30. Hormonal changes, including declining growth hormone and testosterone levels, also contribute. Regular resistance training can significantly slow this decline.