BMR Calculator — Basal Metabolic Rate
Find your Basal Metabolic Rate using three established formulas — Mifflin-St Jeor, Harris-Benedict Original, and Harris-Benedict Revised — and see your TDEE at every activity level.
BMR Formula Comparison
Mifflin-St Jeor (1990)
RecommendedMost accurate
Best validated formula for most adults. Recommended by the Academy of Nutrition and Dietetics. Accuracy: ±10% for ~82% of people.
Harris-Benedict Revised (1984)
Good accuracy
Roza & Shizgal revision of the original Harris-Benedict. More accurate than the original, particularly for normal-weight adults.
Harris-Benedict Original (1919)
Acceptable
The original Harris-Benedict formula. Historical significance but less accurate than modern revisions. Tends to overestimate for obese individuals.
Frequently Asked Questions
What is Basal Metabolic Rate (BMR)?
BMR is the number of calories your body burns at complete rest to maintain basic physiological functions — breathing, circulation, cell production, temperature regulation, and organ function. It represents the minimum calories you need just to stay alive. For most people, BMR accounts for 60–75% of total daily energy expenditure (TDEE). The rest comes from physical activity, digestion (TEF), and non-exercise activity (NEAT).
What is the most accurate BMR formula?
The Mifflin-St Jeor equation (1990) is the most accurate for most adults, validated in multiple independent studies. It predicts measured resting metabolic rate within ±10% for approximately 82% of people. The Harris-Benedict equation (original 1919, revised 1984) is slightly less accurate, particularly for obese individuals. All BMR formulas are estimates — individual variation in actual metabolic rate can be ±15% from any formula.
What is the difference between BMR and TDEE?
BMR is calories burned at rest. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor to account for movement, exercise, and digestion. TDEE is what you actually need each day to maintain weight. For a sedentary person, TDEE ≈ 1.2× BMR. For an athlete training twice daily, TDEE ≈ 1.9× BMR. To lose weight, eat below TDEE; to gain muscle, eat above it.
Why does BMR decrease with age?
BMR decreases approximately 2–3% per decade after age 20, primarily due to age-related muscle loss (sarcopenia). Muscle tissue is metabolically more active than fat tissue — 1 kg of muscle burns approximately 13 kcal/day at rest versus 4 kcal/day for fat tissue. Loss of muscle mass reduces BMR. Regular resistance training and adequate protein intake slow this decline significantly.
Can I increase my BMR?
Yes — the most effective way to increase BMR is to build muscle mass through resistance training. Each kilogram of additional muscle adds approximately 13 kcal/day to your resting metabolism. Consistent activity (NEAT) and adequate protein intake also support a higher metabolic rate. Extreme calorie restriction suppresses BMR through metabolic adaptation — another reason aggressive deficits are counterproductive long-term.