BMR Calculator
Calculate your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest. Compare Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle formulas with optional activity-level calorie estimates.
What is BMR?
BMR stands for Basal Metabolic Rate — the number of calories your body needs to perform its most basic, life-sustaining functions while at complete rest. These include breathing, blood circulation, maintaining body temperature, cellular repair, brain function, and organ activity.
Your BMR represents your body's absolute minimum calorie requirement — the floor below which you should never eat for any extended period. It typically accounts for 60–75% of your total daily calorie burn, making it the single biggest driver of your energy needs.
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Circulation
Heart pumping blood to all organs 24 hours a day.
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Respiration
Lungs breathing and supplying oxygen to cells.
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Thermoregulation
Maintaining steady body temperature around 37 °C.
How BMR is Calculated
Three main formulas are used to estimate BMR. Each uses different coefficients and factors, but all require weight, height, age, and sex as inputs.
Mifflin-St Jeor (Default)
Most AccurateBMR = 10 × kg + 6.25 × cm − 5 × age + 5BMR = 10 × kg + 6.25 × cm − 5 × age − 161Published in 1990, this is the most widely validated formula for estimating BMR across diverse populations. Recommended by major dietetic associations.
Male, 30, 175 cm, 75 kg → BMR = 750 + 1093.75 − 150 + 5 = 1,699 kcalHarris-Benedict
ClassicBMR = 88.362 + 13.397×kg + 4.799×cm − 5.677×ageBMR = 447.593 + 9.247×kg + 3.098×cm − 4.330×ageOriginally developed in 1919 and revised in 1984 (Harris-Benedict Revised). Slightly higher values than Mifflin-St Jeor for most people.
Male, 30, 175 cm, 75 kg → BMR = 88.36 + 1004.8 + 839.8 − 170.3 = 1,762 kcalKatch-McArdle
Body CompositionLBM = weight(kg) × (1 − bodyFat% / 100)BMR = 370 + 21.6 × LBMUses lean body mass instead of total body weight. The most accurate formula when body fat % is known — especially useful for athletes and muscular individuals.
75 kg, 18% body fat → LBM = 61.5 kg → BMR = 370 + 1,328.4 = 1,699 kcalBMR vs TDEE — The Key Difference
| BMR | TDEE | |
|---|---|---|
| Full Name | Basal Metabolic Rate | Total Daily Energy Expenditure |
| Definition | Calories at complete rest | All calories burned in a day |
| Includes | Core organ function only | BMR + movement + digestion |
| Typical % | 60–75% of TDEE | 100% by definition |
| Use it for | Absolute calorie floor | Setting your nutrition target |
BMR tells you the minimum your body needs to survive. TDEE tells you how many calories you actually burn each day including all activity. For practical nutrition planning, always use TDEE — but understanding your BMR helps you set a safe lower bound.
How to Use BMR for Weight Management
Your BMR alone is not your calorie target — you need to account for activity. Multiply your BMR by an activity factor to get your maintenance calories, then adjust for your goal:
0.25–0.5 kg/week fat loss — sustainable and muscle-preserving
Calories in = calories out over time
Lean bulk — minimizes fat gain while supporting muscle growth
Important: Eating below your BMR long-term causes muscle loss, metabolic adaptation, and nutritional deficiencies. Always keep intake at or above BMR.
BMR Calculation Examples
Male · 30 · 175 cm · 75 kg
Sedentary maintenance: 2,039 kcal
Female · 28 · 165 cm · 60 kg
Moderate maintenance: 2,110 kcal
Male · 35 · 180 cm · 90 kg · BF 20%
Katch-McArdle uses LBM = 72 kg
Female · 45 · 160 cm · 65 kg
Light activity maintenance: 1,790 kcal
Frequently Asked Questions
What is a normal BMR?
BMR varies widely by age, sex, height, and weight. Typical ranges: adult women 1,200–1,600 kcal/day; adult men 1,500–2,100 kcal/day. BMR decreases with age (roughly 1–2% per decade after 30) and increases with greater muscle mass or body size.
Which BMR formula is the most accurate?
Mifflin-St Jeor (1990) is the most commonly recommended formula for the general population. It outperforms the original Harris-Benedict formula in most validation studies. If you know your body fat percentage, Katch-McArdle is more accurate — especially for athletes with relatively low body fat.
Can I eat exactly at my BMR?
For very short periods (e.g., doctor-supervised very low calorie diets), eating near BMR can be done, but it's not sustainable or recommended long-term. Consistently eating at or below BMR leads to muscle loss, nutrient deficiencies, fatigue, and metabolic adaptation. Always use TDEE as your calorie baseline.
Does BMR change over time?
Yes. BMR decreases as you age due to muscle loss (sarcopenia) — roughly 2–3% per decade after age 30. It also drops during prolonged caloric restriction (metabolic adaptation). Resistance training and adequate protein intake help preserve muscle mass and maintain a higher BMR as you age.
Why is my BMR different from other calculators?
Different calculators may use different formulas (Mifflin-St Jeor, Harris-Benedict, Cunningham, etc.) or may round intermediate values differently. A difference of ±50–100 kcal between calculators using different formulas is normal and expected. Mifflin-St Jeor and Harris-Benedict typically differ by 2–5% for most adults.
What is lean body mass and why does it affect BMR?
Lean Body Mass (LBM) is the portion of your body that is not fat — muscles, organs, bones, blood, and water. Muscle tissue is metabolically active and burns far more calories at rest than fat tissue (~13 kcal/kg/day vs ~4.5 kcal/kg/day). People with higher muscle mass therefore have higher BMRs, which is why the Katch-McArdle formula (which uses LBM) is more accurate for muscular individuals.