BMR Calculator

Understanding Basal Metabolic Rate

Your BMR is the energy your body needs for basic survival functions while lying completely still. It powers your heart, lungs, brain, and cellular repair. For most people, BMR is the single largest component of daily calorie burn, far exceeding exercise. The Mifflin-St Jeor equation calculates BMR using weight, height, age, and sex.^[1] Multiply your BMR by an activity factor to get your TDEE, which is the number you actually eat against for weight management.

BMR by Age and Activity Level

How Basal Metabolic Rate Is Calculated

Your basal metabolic rate represents the minimum energy your body requires at complete rest to maintain vital functions — breathing, circulation, cell production, nutrient processing, and temperature regulation. BMR accounts for 60–75% of total daily energy expenditure for most people, making it the single largest component of your caloric needs. This calculator uses the Mifflin-St Jeor equation, which research has shown to be the most accurate predictive formula for modern populations: for men, BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5; for women, the same formula minus 161. The Harris-Benedict equation, developed in 1919 and revised in 1984, tends to overestimate BMR by 5–15% in overweight individuals. Katch-McArdle formula incorporates lean body mass directly, making it more accurate for muscular or lean individuals when body fat percentage is known.

BMR by Age, Weight, and Gender

Factors That Affect Your BMR

Muscle mass is the largest controllable factor — muscle tissue burns approximately 6 calories per pound per day at rest, while fat tissue burns roughly 2 calories per pound. Adding 10 pounds of muscle through resistance training increases BMR by about 40 calories per day, or 14,600 calories per year — equivalent to roughly 4 pounds of fat. Age reduces BMR by approximately 1–2% per decade after age 20, primarily due to muscle loss (sarcopenia) rather than aging itself, which means strength training can partially offset age-related metabolic decline. Genetics account for roughly 5–10% of individual BMR variation. Thyroid function significantly affects metabolic rate — hypothyroidism can reduce BMR by 15–40%, while hyperthyroidism can increase it by 30–100%. Chronic caloric restriction (crash dieting) can suppress BMR by 15–25% through metabolic adaptation, a survival mechanism that makes sustained weight loss increasingly difficult. Use our TDEE Calculator to add activity level to your BMR for total daily calorie needs.

BMR and Weight Management

Understanding BMR prevents the most common dieting mistake: eating below your basal metabolic rate. Consuming fewer calories than your BMR for extended periods triggers metabolic adaptation — your body slows its metabolic rate to conserve energy, making weight loss progressively harder and weight regain likely. A sustainable caloric deficit targets 500–750 calories below your total daily energy expenditure (TDEE, which is BMR multiplied by your activity factor), not below BMR itself. For a person with a 1,700-calorie BMR and a 1.55 activity factor (moderately active), TDEE is approximately 2,635 calories. A 500-calorie deficit (2,135 calories daily) produces roughly 1 pound of fat loss per week without triggering excessive metabolic compensation. Never consume below your BMR except under medical supervision — this ensures your body receives enough energy to maintain organ function, immune response, and hormonal balance. Track your intake with our Calorie Calculator and plan macronutrient ratios using our Macro Calculator.

Activity Multipliers and Total Daily Energy Expenditure

These multipliers convert BMR to Total Daily Energy Expenditure (TDEE) — the total calories you burn in a full day including all activity. Most people overestimate their activity level — unless you exercise intensely for 60+ minutes most days, "moderately active" is likely the appropriate selection. Choosing "very active" when you are actually moderately active overestimates your caloric needs by nearly 300 calories per day, which can stall weight loss or cause unintended weight gain over months. Be honest about your activity level for accurate results, and adjust as your exercise habits change.

BMR Comparison Across Equations

The Mifflin-St Jeor equation consistently produces the most accurate BMR estimates across diverse populations, which is why it is the default in this calculator and is recommended by the Academy of Nutrition and Dietetics. The Katch-McArdle formula requires knowing your body fat percentage but is more accurate for muscular individuals whose lean mass deviates significantly from population averages. If you know your body fat percentage, use our Body Fat Calculator and then apply the Katch-McArdle formula for a more personalized estimate.

How Sleep Affects Your Metabolic Rate

Sleep deprivation — even moderate restriction of 5–6 hours per night — reduces resting metabolic rate by 2–8% and alters hormones that regulate hunger and energy expenditure. Poor sleep increases ghrelin (the hunger hormone) by 15–30% and decreases leptin (the satiety hormone) by a similar margin, creating a hormonal environment that drives overeating. Studies show sleep-deprived individuals consume 300–500 additional calories per day, predominantly from high-carbohydrate snacks. The metabolic impact extends beyond appetite: insufficient sleep reduces insulin sensitivity by 25–30%, impairing your body's ability to process glucose efficiently and increasing fat storage tendency. For anyone focused on body composition — whether gaining muscle or losing fat — 7–9 hours of quality sleep is as important as diet and exercise. See our Sleep Calculator to optimize your sleep schedule for metabolic health.

Metabolic Adaptation and Reverse Dieting

After extended periods of caloric restriction, metabolic adaptation reduces your BMR below what the equations predict — sometimes by 15–25%. This "metabolic damage" is actually a normal physiological response to sustained energy deficit: your body becomes more efficient, reducing non-essential energy expenditure through lower body temperature, reduced fidgeting (NEAT), decreased thyroid hormone output, and reduced muscle protein synthesis. Reverse dieting — gradually increasing calories by 50–100 per week back toward maintenance — allows your metabolism to recover without rapid fat gain. A person who has dieted at 1,400 calories for months might reverse diet by adding 75 calories per week, reaching 1,800 over approximately 5 weeks, then reassessing. This patient approach restores metabolic rate, improves energy and workout performance, and establishes a higher maintenance intake from which future fat loss phases can begin more effectively. The key indicators that metabolic recovery is progressing include improved workout performance, increased body temperature, better sleep quality, and stabilized hunger levels — these collectively signal that your hormonal environment and thyroid function are normalizing after the stress of prolonged caloric restriction. See our Body Fat Calculator to track composition changes alongside metabolic recovery.

Understanding Basal Metabolic Rate

Your Basal Metabolic Rate represents the number of calories your body burns at complete rest to maintain vital functions — breathing, circulation, cell production, temperature regulation, and brain activity. BMR typically accounts for 60% to 75% of total daily energy expenditure, making it the single largest component of your calorie burn. The remaining calories are burned through physical activity (15-30%), the thermic effect of food (approximately 10%), and non-exercise activity thermogenesis (NEAT) — fidgeting, walking, maintaining posture, and other involuntary movements that vary significantly between individuals.

BMR Estimation Formulas Compared

Factors That Affect BMR

Muscle mass is the most significant controllable factor affecting BMR. Muscle tissue burns approximately 6 calories per pound per day at rest, while fat tissue burns only 2 calories per pound. Adding 10 pounds of muscle through strength training increases daily BMR by approximately 40 to 60 calories — modest per day but meaningful over time (4,000 to 6,000 extra calories burned per year). Age reduces BMR by approximately 1% to 2% per decade after age 20, primarily due to declining muscle mass and hormonal changes. This age-related decline is significantly mitigated by maintaining an active strength training routine. Genetics influence BMR by 5% to 15%, explaining why some individuals seem to burn calories more efficiently than others despite similar body composition.

Thyroid function directly regulates metabolic rate — hypothyroidism can reduce BMR by 15% to 40%, while hyperthyroidism can increase it by 10% to 25%. If your actual calorie needs differ dramatically from calculated BMR estimates, thyroid testing may be warranted. Body temperature, climate, and caffeine intake also modestly affect BMR. Sleep deprivation reduces BMR by approximately 5% to 20% and increases hunger hormones, creating a double effect on weight management. For calorie needs including activity, use our Calorie Calculator.

From BMR to Total Daily Energy Expenditure

BMR and Weight Management

Understanding your BMR is the foundation of any evidence-based weight management plan. To lose weight, you need a calorie deficit — consuming fewer calories than your TDEE. A deficit of 500 calories per day produces approximately 1 pound of fat loss per week (3,500 calories per pound). However, creating a deficit below your BMR is counterproductive: consuming fewer calories than your body needs for basic functions triggers metabolic adaptation (your body reduces BMR to conserve energy), muscle loss (the body breaks down protein for fuel), hormonal disruption (reduced thyroid function, increased cortisol, disrupted leptin and ghrelin), and decreased energy and cognitive function. A sustainable approach targets a deficit of 15% to 25% below TDEE while keeping intake above BMR. For a person with a BMR of 1,700 and TDEE of 2,400, the optimal deficit range is 1,800 to 2,040 calories daily.

Metabolic Adaptation and Dieting

Prolonged calorie restriction causes metabolic adaptation — your BMR decreases beyond what would be predicted by weight loss alone. After losing 20 pounds, your BMR might drop by 250 calories per day rather than the expected 150 based on reduced body mass. This additional 100-calorie reduction is metabolic adaptation — the body's attempt to conserve energy in response to perceived scarcity. Research from the National Institutes of Health found that contestants from a televised weight loss show experienced metabolic adaptation that persisted 6 years after the competition, with BMR remaining 500+ calories below expected levels. Strategies to minimize metabolic adaptation include incorporating periodic diet breaks (eating at maintenance for 1-2 weeks every 6-12 weeks of deficit), strength training to preserve muscle mass, adequate protein intake (0.7 to 1.0 grams per pound of body weight), gradual rather than extreme deficits, and reverse dieting (gradually increasing calories after a diet phase). For body composition tracking, see our Body Fat Calculator and BMI Calculator.

How to Use This Calculator

1. Enter your stats — Weight, height, age, and biological sex.
2. Compare formulas — Toggle between Mifflin-St Jeor and Harris-Benedict.
3. Apply activity multiplier — Select your activity level to estimate TDEE.

Tips and Best Practices

See also: TDEE Calculator · Calorie Calculator · Macro Calculator · Calorie Deficit