BMR Calculator
Find your daily calorie burn at rest (BMR) and total daily energy expenditure (TDEE).
🔥 What is BMR?
Basal Metabolic Rate (BMR) is the minimum number of calories your body needs to sustain essential life functions while at complete rest - in a warm environment, in a post-absorptive state, and not engaged in any physical activity. These essential functions include breathing, blood circulation, maintaining body temperature, cell production, protein synthesis, and the constant operation of organs such as the heart, liver, kidneys, and brain.
BMR is often confused with Resting Metabolic Rate (RMR), which is slightly higher because RMR is measured under less strict conditions. In practical terms, the two values are close enough that they are used interchangeably in most nutrition and fitness contexts.
Understanding your BMR is the first step in accurately determining your total daily calorie needs. Once you know your BMR, you multiply it by an activity factor to get your Total Daily Energy Expenditure (TDEE) - the number of calories you need each day accounting for your actual movement and exercise. This TDEE figure is the single most important number for designing an effective diet for weight loss, maintenance, or muscle gain.
The most widely validated formula for estimating BMR is the Mifflin-St Jeor equation, developed in 1990 and shown to be accurate within 10% for most adults. It accounts for weight, height, age, and biological sex. This calculator uses Mifflin-St Jeor as its primary formula because research consistently shows it outperforms the older Harris-Benedict equation in predicting actual resting energy expenditure.
Factors that influence BMR include body composition (more muscle = higher BMR), age (BMR declines gradually with age), sex (males generally have higher BMR due to greater muscle mass), genetics, hormonal status (thyroid function in particular), and ambient temperature. BMR is not fixed - it responds to changes in body composition and metabolic health over time.
📐 BMR Formula (Mifflin-St Jeor)
To calculate TDEE, multiply BMR by the appropriate activity factor:
📖 How to Use This Calculator
Steps to Calculate Your BMR and TDEE
💡 Example Calculations
Example 1 — 35-year-old Male, 80 kg, 178 cm, Moderately Active
Example 2 — 28-year-old Female, 60 kg, 163 cm, Lightly Active
❓ Frequently Asked Questions
🔗 Related Calculators
What is BMR and why does it matter?
BMR (Basal Metabolic Rate) is the number of calories your body needs to sustain basic physiological functions - breathing, circulation, cell repair, and body temperature regulation - while at complete rest. It matters because it forms the foundation of your total daily energy expenditure (TDEE). If you consume fewer calories than your TDEE, you lose weight; more, you gain weight.
What is the difference between BMR and TDEE?
BMR is your calorie burn at complete rest. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor that accounts for movement, exercise, and daily activity. TDEE is the more useful number for setting calorie targets because it reflects your actual daily energy need.
Which BMR formula is most accurate - Mifflin-St Jeor or Harris-Benedict?
Research consistently shows that the Mifflin-St Jeor equation (1990) is more accurate than the original Harris-Benedict equation (1919) for most modern adults. A 2005 study in the Journal of the American Dietetic Association found Mifflin-St Jeor predicted RMR within 10% for 82% of subjects, compared to 72% for Harris-Benedict. This calculator uses Mifflin-St Jeor.
How do I use BMR to lose weight?
Calculate your TDEE using your BMR and activity level. Then subtract 300–500 calories from your TDEE to create a moderate deficit. This typically results in 0.3–0.5 kg of weight loss per week, which is considered a safe and sustainable rate. Avoid cutting more than 500 calories below TDEE without medical supervision.
Does BMR change with age?
Yes. BMR naturally declines with age, primarily because muscle mass tends to decrease after the mid-30s (a process called sarcopenia). Research suggests BMR drops by about 1–2% per decade after age 20. Regular strength training and adequate protein intake are the most effective strategies to slow this decline.
What is a normal BMR for a 30-year-old woman?
For a 30-year-old woman at average height (163 cm) and weight (65 kg), the Mifflin-St Jeor formula gives a BMR of approximately 1,440 calories per day. With moderate activity (3-4 days/week exercise), her TDEE is approximately 1,440 x 1.55 = 2,232 calories/day. BMR typically ranges from 1,300 to 1,600 calories for most adult women.
How does age affect BMR?
BMR naturally declines with age, primarily due to loss of lean muscle mass (sarcopenia). Research suggests BMR decreases by roughly 1-2% per decade after age 30. The best way to counteract this decline is resistance training, which preserves muscle mass and keeps metabolic rate higher as you age.
Can I use BMR to calculate how many calories I need to maintain weight?
BMR is just the base - multiply by an activity factor to get TDEE (Total Daily Energy Expenditure). Sedentary (desk job, no exercise): BMR x 1.2. Lightly active (1-3 days/week exercise): BMR x 1.375. Moderately active (3-5 days): BMR x 1.55. Very active (6-7 days hard exercise): BMR x 1.725. Eat at TDEE to maintain weight, below to lose, above to gain.