BMR Calculator

Your Basal Metabolic Rate (BMR) is the number of calories your body burns if you stayed in bed all day—just to keep your heart beating, lungs breathing, brain functioning, and body temperature regulated. It accounts for 60-75% of your total daily calorie expenditure. Understanding your BMR is the first step to any successful weight management plan.

Why BMR Varies Between Individuals

BMR is not the same for everyone. Factors that increase BMR:

• More Lean Muscle Mass: Muscle burns 6-10 calories per pound per day vs fat which burns 2-3 calories. A muscular person burns more calories at rest.
• Larger Body Size: Taller, heavier people have higher BMR because they have more cells to maintain.
• Younger Age: BMR declines 1-2% per decade after age 20 due to hormonal changes and muscle loss.
• Male Sex: Men typically have higher BMR due to greater muscle mass and larger body size.
• Fever or Illness: Each 0.5°C (0.9°F) increase in body temperature raises BMR by 7%.
• Pregnancy/Lactation: BMR increases to support fetal growth and milk production.

How to Calculate BMR: Multiple Formulas

1. Mifflin-St Jeor (1990) - Most Accurate for General Population

• Men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5
• Women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161

2. Harris-Benedict (Revised 1984) - Older, Still Used Clinically

• Men: BMR = 88.362 + (13.397 × kg) + (4.799 × cm) - (5.677 × age)
• Women: BMR = 447.593 + (9.247 × kg) + (3.098 × cm) - (4.330 × age)

3. Katch-McArdle - Requires Body Fat %, Most Accurate for Lean Individuals

• BMR = 370 + (21.6 × Lean Body Mass in kg)
• This formula accounts for actual muscle mass, making it superior for athletes and bodybuilders.

4. Cunningham (1980) - For Very Lean Athletes

• BMR = 500 + (22 × Lean Body Mass in kg)

Example Calculation Comparison (35 year old man, 180 lbs/81.6 kg, 5'10"/178 cm, 15% body fat):

• Mifflin-St Jeor: 1,759 calories
• Harris-Benedict: 1,774 calories (+0.9% difference)
• Katch-McArdle: LBM = 81.6 × 0.85 = 69.4 kg → BMR = 370 + (21.6 × 69.4) = 1,867 calories (+6% difference)

From BMR to TDEE (Total Daily Energy Expenditure)

Your TDEE = BMR × Activity Factor. Multiply your BMR by the factor that best describes your lifestyle:

Metabolic Adaptation: Why Weight Loss Slows

As you lose weight, your BMR decreases for two reasons:

1. You weigh less: Fewer cells to maintain (expected).

2. Metabolic adaptation: Your body becomes more efficient, lowering BMR more than predicted by weight loss alone. Research shows BMR can drop 10-15% beyond expected after significant weight loss. This "adaptive thermogenesis" is your body's defense against starvation. Strategies to counteract:

• Refeed days: Eat at maintenance 1-2 days/week
• Diet breaks: Take 2 weeks at maintenance every 8-12 weeks of dieting
• Resistance training: Preserves muscle mass, which burns calories
• NEAT increase: Non-Exercise Activity Thermogenesis (fidgeting, walking, standing)

Boosting Your BMR: Myth vs Reality

Effective strategies:

• Build muscle: Each pound of muscle burns 30-50 more calories per day than fat. Gaining 10 lbs of muscle increases BMR by 300-500 calories.
• Protein intake: The thermic effect of food (TEF) for protein is 20-30% (vs 5-10% for carbs, 0-3% for fat). Eating protein burns more calories during digestion.
• Cold exposure: Shivering increases metabolic rate 2-5x. Non-shivering thermogenesis (brown fat activation) may play a role.
• Green tea/caffeine: Transient 4-5% increase, but tolerance develops.

Ineffective or dangerous strategies:

• Starvation diets: Below 1200 calories crashes BMR, causes muscle loss. When you resume normal eating, you'll gain fat faster.
• Magic pills: No supplement safely raises BMR beyond 5-10%. Most contain caffeine or dangerous stimulants.
• Thyroid hormones: Only for medical hypothyroidism. Misuse causes heart arrhythmias, bone loss.

FAQ: BMR Calculator

BMR Calculator is optimized for fast browser-based use, so you can test multiple scenarios in seconds.