BMR Calculator
Basal Metabolic Rate
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BMR (Mifflin-St Jeor)
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calories / day at rest
Formula Comparison
Mifflin-St Jeor Recommended
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Harris-Benedict (revised)
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TDEE by Activity Level
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What Is BMR?
BMR (Basal Metabolic Rate) is the number of calories your body needs to maintain basic physiological functions at complete rest — breathing, circulation, cell repair, temperature regulation. It represents 60-75% of total daily calorie expenditure for most people.
Two main formulas exist: Mifflin-St Jeor (1990) is currently the most accurate for the general population, validated in multiple studies. Harris-Benedict (revised 1984) is the older standard, still widely used but tends to overestimate by 5%.
BMR is the foundation for calculating TDEE — your total daily energy expenditure including activity. Multiply BMR by your activity factor to get the calories you actually need each day.
BMR estimates can vary by 10-15% from actual metabolic rate. Consult a healthcare professional for personalized nutrition advice.
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BMR Questions
What is the difference between BMR and TDEE?+
BMR is the calories burned at complete rest — if you stayed in bed all day. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor to account for exercise, movement, and daily activities. TDEE is what most nutrition plans are based on.
Which BMR formula is most accurate?+
The Mifflin-St Jeor equation is generally considered the most accurate for the general population. A 2005 study in the Journal of the American Dietetic Association found it predicted resting energy expenditure within 10% in 82% of participants. The Katch-McArdle formula is more accurate for lean individuals as it uses lean body mass instead of total weight.
Does BMR change with age?+
Yes. BMR decreases by approximately 1-2% per decade after age 20, primarily due to muscle mass loss (sarcopenia). This is why calorie needs decrease with age and why maintaining muscle through resistance training becomes more important. Hormonal changes, particularly around menopause, also affect BMR.
How can I increase my BMR?+
The most effective way is building muscle through resistance training — muscle tissue burns more calories at rest than fat tissue. Other factors: eating sufficient protein (thermic effect of food is highest for protein at 20-30%), avoiding prolonged very low-calorie diets that trigger metabolic adaptation, staying hydrated, and getting adequate sleep.