BMR Calculator

About BMR Calculator

Our BMR (Basal Metabolic Rate) Calculator helps you determine how many calories your body burns at complete rest to maintain basic physiological functions like breathing, circulation, cell production, and nutrient processing. BMR represents the minimum energy required to keep your body alive in a resting state—it's the foundation for understanding your total daily calorie needs and creating effective weight loss, maintenance, or gain plans. BMR accounts for 60-75% of your total daily energy expenditure for most people, making it the single largest component of calorie burn. The remaining calories come from physical activity, digestion (thermic effect of food), and non-exercise activity thermogenesis (NEAT—fidgeting, posture, daily movements). Our calculator uses the Mifflin-St Jeor equation, which is currently considered the most accurate formula for estimating BMR: For men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161. This equation was developed in 1990 and has been validated across diverse populations, making it more reliable than older formulas like Harris-Benedict. Understanding your BMR is crucial for: weight loss (eat below total daily energy expenditure but not below BMR for healthy fat loss), weight gain (eat above TDEE to build muscle), nutrition planning (ensure adequate nutrient intake), fitness optimization (fuel your workouts properly), and metabolic health (understand how your metabolism changes with age, weight, and body composition). BMR is influenced by multiple factors: muscle mass (muscle burns more calories than fat, even at rest), age (metabolism slows 2-3% per decade after age 30), sex (men typically have higher BMR due to more muscle mass), genetics (can vary 20-30% between individuals), hormones (thyroid function significantly impacts metabolism), and body temperature (fever increases BMR significantly). It's important to note that BMR alone doesn't tell you how many calories to eat—you need to multiply BMR by an activity factor to get TDEE (Total Daily Energy Expenditure), which represents actual daily calorie needs including all activities. However, knowing your BMR provides the baseline from which all calorie calculations begin, making it an essential metric for anyone serious about managing their weight, optimizing nutrition, or understanding their body's energy requirements.

Key Features

Mifflin-St Jeor Formula

Uses the most accurate and scientifically validated formula for BMR calculation from 1990 research

Gender-Specific Calculations

Accounts for metabolic differences between men and women with separate formulas

Imperial & Metric Support

Enter weight in pounds or kilograms, height in feet/inches or centimeters for convenience

Activity Level Multipliers

Shows TDEE (Total Daily Energy Expenditure) by applying activity factors from sedentary to very active

Detailed Calorie Breakdown

Displays BMR plus estimated calories burned from activity for complete daily energy picture

Age & Height Considerations

Factors in age-related metabolic decline and height's impact on energy requirements

Real-time Results

Instant BMR calculation as you enter your metrics—no delays or button clicking required

Weight Goals Guidance

Use BMR results to determine calorie targets for weight loss, maintenance, or muscle gain goals

How to Use the BMR Calculator

Select Your Gender

Choose male or female, as this significantly affects BMR calculation due to typical differences in muscle mass and hormones.

Enter Your Age

Input your age in years. Metabolism naturally slows with age, typically 2-3% per decade after age 30.

Input Your Weight

Enter your current weight in pounds or kilograms. More body mass requires more energy to maintain.

Enter Your Height

Input your height in feet/inches or centimeters. Taller individuals typically have higher BMR due to larger body surface area.

Review Your BMR

See your Basal Metabolic Rate—the calories burned at complete rest maintaining basic body functions.

Check Activity-Adjusted Calories

Review TDEE estimates for different activity levels to understand your actual daily calorie needs including exercise and movement.

BMR & Metabolism Tips

Focus on TDEE, Not Just BMR: BMR is just your baseline—TDEE (Total Daily Energy Expenditure) is what actually matters for weight management. Calculate TDEE by multiplying BMR by activity factor: sedentary (×1.2), lightly active (×1.375), moderately active (×1.55), very active (×1.725), extremely active (×1.9). Then create calorie deficit/surplus from TDEE. For weight loss, eat 15-25% below TDEE, which keeps you well above BMR while creating sustainable fat loss of 0.5-2 lbs per week.
Build and Maintain Muscle: Muscle is your metabolic engine—it burns calories 24/7, even at rest. Prioritize strength training 3-5 times per week with progressive overload (gradually increasing weight/reps). Eat adequate protein (0.7-1g per lb body weight) to support muscle growth and prevent muscle loss during weight loss. Even modest muscle gains (10-20 lbs over years) meaningfully increase BMR and TDEE, making weight management easier long-term. Muscle also improves body composition, strength, and functional fitness.
Never Chronically Eat Below BMR: Your BMR is the minimum energy for essential body functions—consistently eating below it causes metabolic damage, muscle loss, hormonal issues, and rebound weight gain. Even aggressive fat loss should keep intake at or slightly above BMR. If your BMR is 1,500 and TDEE is 2,100, eat 1,600-1,800 for weight loss—never below 1,500. Extreme restriction (1,000-1,200 calories) might seem faster but causes metabolic slowdown that makes long-term success nearly impossible.
Adjust Calculations to Real Results: BMR calculators provide estimates—your actual metabolism might differ by 10-20%. Track weight and calories consistently for 4 weeks, then adjust. If eating "maintenance" calories but losing 1 lb/week, your actual TDEE is 500 calories higher—eat more. If gaining weight, actual TDEE is lower—reduce intake. Your body's response is the truth, not the calculator. Use calculations as starting points, then personalize based on results.
Account for Metabolic Adaptation: During prolonged calorie restriction, your body adapts by reducing BMR, NEAT (fidgeting, movement), and TDEE beyond what's expected from weight loss alone. This adaptive thermogenesis can reduce TDEE by 10-15% beyond prediction. Combat it with: diet breaks (eat at maintenance for 1-2 weeks every 8-12 weeks), refeed days (higher carb days weekly), adequate protein, strength training, and avoiding extreme deficits. If plateau occurs for 3-4 weeks, consider 2-week maintenance break to restore metabolism before resuming deficit.
Optimize for Long-term Metabolic Health: Crash diets, extreme restrictions, and rapid weight loss damage long-term metabolism. Instead: lose weight slowly (0.5-1% body weight per week), maintain muscle through strength training and protein, eat at maintenance periodically, prioritize sleep (7-9 hours), manage stress, and stay active with both exercise and daily movement. A healthy, robust metabolism makes weight management easier for life. Short-term thinking (lose 20 lbs in 6 weeks) often creates long-term problems (regain 30 lbs with slower metabolism). Think in years, not weeks.

Frequently Asked Questions

What is BMR and why is it important?

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to maintain essential physiological functions: breathing, heartbeat, circulation, cell production, nutrient processing, and maintaining body temperature. It's measured in a perfectly resting state—lying down in a temperature-neutral environment after 12 hours of fasting. BMR typically accounts for 60-75% of your total daily calorie expenditure, making it the largest component of your energy needs. Understanding BMR is crucial for: (1) Weight management—you need to know your baseline calorie burn to create appropriate calorie deficits (for weight loss) or surpluses (for muscle gain). (2) Nutrition planning—ensures you're eating enough to support basic body functions even when dieting. (3) Fitness optimization—helps calculate how many calories to eat to fuel workouts while achieving body composition goals. (4) Health assessment—unusually low BMR might indicate thyroid issues or metabolic disorders. BMR is different from TDEE (Total Daily Energy Expenditure)—BMR is just resting calories, while TDEE includes BMR plus activity, exercise, and digestion. Most people need 1.3-2.0x their BMR depending on activity level.

How accurate is the BMR calculator?

The Mifflin-St Jeor equation used by our calculator is considered the most accurate prediction formula, with typical accuracy within ±10% for most people. It was developed from data on thousands of individuals and validated across diverse populations. However, BMR calculators provide estimates, not exact measurements—individual variation exists. Factors affecting accuracy: (1) Body composition—people with more muscle mass have higher BMR than predicted (muscle is metabolically active), while those with more body fat have lower BMR. (2) Genetics—metabolic rate can vary 20-30% between individuals with same stats. (3) Hormones—thyroid conditions, PCOS, and other hormonal issues affect metabolism. (4) Dieting history—chronic dieting can reduce BMR through metabolic adaptation. (5) Medications—some drugs affect metabolism. For most accurate measurement, professional testing is required: indirect calorimetry (breathing test measuring oxygen consumption) or DEXA scans combined with metabolic testing. These clinical tests cost $100-300. For general population, calculator estimates are sufficient for planning purposes. If you find weight changes don't match expectations based on calculated BMR, adjust calories empirically—your actual metabolism is what matters, and these formulas are starting points.

What is the difference between BMR and TDEE?

BMR (Basal Metabolic Rate) is calories burned at complete rest. TDEE (Total Daily Energy Expenditure) is total calories burned including all activities. TDEE = BMR × Activity Factor + Thermic Effect of Food. Components: (1) BMR: 60-75% of TDEE—the baseline for keeping you alive. (2) Activity & Exercise: 15-30% of TDEE—gym workouts, sports, deliberate exercise. (3) NEAT (Non-Exercise Activity Thermogenesis): 5-10% of TDEE—fidgeting, posture, walking around, daily movements. (4) TEF (Thermic Effect of Food): 8-15% of TDEE—calories burned digesting food (protein burns most). Example: 30-year-old woman, 140 lbs, 5'5", BMR = 1,380 calories. Sedentary (little exercise): TDEE = 1,380 × 1.2 = 1,656 calories. Moderate activity (exercise 3-5x/week): TDEE = 1,380 × 1.55 = 2,139 calories. Very active (exercise 6-7x/week): TDEE = 1,380 × 1.725 = 2,381 calories. For weight loss, create deficit from TDEE, not BMR. Never eat below BMR consistently—this deprives your body of energy for basic functions, slows metabolism, and is unsustainable. Healthy deficit: 15-25% below TDEE, which keeps you well above BMR while losing 0.5-2 lbs per week.

Why do men typically have higher BMR than women?

Men typically have 5-10% higher BMR than women of the same age, weight, and height due to physiological differences: (1) Muscle mass—men naturally have 30-40% more muscle mass than women due to higher testosterone. Muscle tissue burns 6-10 calories per pound per day, while fat burns only 2-3 calories. More muscle = higher BMR. (2) Body fat percentage—women naturally carry 8-10% more body fat for reproductive functions. Higher body fat percentage means lower metabolic rate. (3) Hormones—testosterone promotes muscle growth and higher metabolism; estrogen promotes fat storage and lower metabolism. (4) Body size—men are typically larger (taller, heavier) requiring more energy for basic functions. Example: Man: 30 years, 180 lbs, 5'10" → BMR ≈ 1,850 calories. Woman: 30 years, 140 lbs, 5'5" → BMR ≈ 1,380 calories. This isn't "unfair"—it's biological reality. Women need fewer calories because their bodies require less energy for baseline functioning. The Mifflin-St Jeor formula accounts for this with different constants: men get +5, women get -161. This 166-calorie difference reflects typical sex-based metabolic differences. Women shouldn't compare calorie needs to men directly—focus on your individual TDEE and adjust based on your goals and results.

Does BMR decrease with age?

Yes, BMR decreases approximately 2-3% per decade after age 30, or about 100-150 calories per decade for average adults. This age-related metabolic decline occurs due to: (1) Muscle loss—sarcopenia (age-related muscle loss) occurs at 3-8% per decade after 30, accelerating after 60. Less muscle = lower BMR. (2) Hormonal changes—growth hormone, testosterone, and thyroid hormone levels decline with age, reducing metabolic rate. (3) Cellular changes—mitochondrial efficiency decreases, cell turnover slows. (4) Activity reduction—people typically become less active with age, further reducing muscle mass and metabolism. Example: At age 30, BMR might be 1,800 calories. At age 50, BMR might be 1,650 calories (8% decline). At age 70, BMR might be 1,500 calories (17% decline). This explains "middle-age weight gain"—eating the same calories at 50 as at 30 creates a surplus because TDEE dropped 200+ calories. However, metabolic decline isn't inevitable—it can be minimized: (1) Strength training—maintains muscle mass, the primary factor in BMR. (2) High protein intake—preserves muscle and has higher thermic effect. (3) Stay active—maintains NEAT and prevents muscle loss. (4) Manage hormones—address thyroid issues, consider HRT if appropriate. Active 60-year-olds with good muscle mass can have higher BMR than sedentary 30-year-olds. Age is just one factor—body composition matters more.

Should I eat below my BMR to lose weight faster?

No, consistently eating below BMR is counterproductive and potentially harmful. BMR represents the minimum calories your body needs for essential functions—breathing, heartbeat, organ function, cell repair, immune system, hormone production. Eating below BMR causes: (1) Metabolic adaptation—body dramatically slows metabolism to conserve energy, making further weight loss harder. (2) Muscle loss—body breaks down muscle for energy when intake is too low, further reducing BMR. (3) Hormonal disruption—thyroid function decreases, cortisol increases, leptin drops, reproductive hormones crash. (4) Energy crashes—fatigue, brain fog, poor workouts, decreased NEAT. (5) Nutrient deficiencies—insufficient calories means insufficient vitamins, minerals, protein. (6) Unsustainability—extreme restriction leads to binge eating and regaining weight. Proper weight loss approach: (1) Calculate TDEE (BMR × activity factor). (2) Create 15-25% deficit from TDEE, not BMR. Example: TDEE = 2,000 calories, BMR = 1,400. Eat 1,500-1,700 calories (below TDEE, above BMR). This creates 0.5-1 lb/week loss while supporting body functions. (3) Never eat below BMR for extended periods. (4) If plateau occurs, adjust TDEE estimate downward slightly or increase activity—don't slash calories below BMR. Extreme low-calorie diets (800-1,000 calories) should only occur under medical supervision for specific medical reasons, not for general weight loss.

Can I increase my BMR?

Yes, you can increase BMR primarily through building muscle mass, though effects are modest. Strategies: (1) Strength training—muscle burns 6-10 cal/lb/day vs. 2-3 for fat. Gaining 10 lbs of muscle increases BMR by ~50-80 calories daily. Progressive resistance training 3-5x/week builds muscle over months to years. (2) Increase protein intake—protein has highest thermic effect (20-30% vs. 5-10% for carbs, 0-3% for fat) and supports muscle growth. Aim for 0.7-1g per pound of body weight. (3) Stay active—regular exercise and high NEAT maintain metabolism; sedentary lifestyle reduces it. (4) Don't over-restrict calories—chronic severe deficits suppress BMR through metabolic adaptation. Eat adequate calories (at least BMR). (5) Get sufficient sleep—sleep deprivation reduces metabolism and increases hunger hormones. (6) Manage stress—chronic cortisol elevation promotes muscle breakdown and fat storage. (7) Stay hydrated—dehydration can reduce metabolic rate. (8) Consider cold exposure—cold thermogenesis slightly increases calorie burn (modest effect). (9) Address thyroid—hypothyroidism significantly reduces BMR; proper treatment normalizes it. Realistic expectations: Building 20 lbs of muscle might increase BMR by 100-150 calories—helpful but not transformative. Focus on TDEE (which you can increase significantly through activity) rather than obsessing over BMR. A daily 30-minute workout burns 200-400 calories plus builds muscle—much more impactful than trying to maximize BMR alone. The goal isn't maximizing BMR—it's creating sustainable calorie balance through appropriate intake and activity for your goals.

How does body composition affect BMR calculations?

BMR calculators use weight, height, age, and sex as proxies for body composition, but don't directly measure muscle vs. fat. This creates accuracy limitations: Two people with identical stats can have very different BMRs due to body composition differences. Example: Person A: 180 lbs, 12% body fat (158 lbs lean mass, 22 lbs fat) → BMR might be 1,950 calories. Person B: 180 lbs, 30% body fat (126 lbs lean mass, 54 lbs fat) → BMR might be 1,650 calories. That's a 300-calorie difference despite identical height, weight, age, and sex! Why: Muscle is metabolically active tissue burning ~6-10 cal/lb/day. Fat is storage tissue burning only ~2-3 cal/lb/day. Lean body mass is the primary determinant of BMR. Standard calculators estimate "average" body composition for your stats. If you're very muscular, your actual BMR is higher than calculated. If you have high body fat percentage, actual BMR is lower. More accurate methods: (1) Katch-McArdle formula—uses lean body mass if known (requires body fat testing). (2) DEXA scan—measures exact body composition, provides most accurate metabolic estimates. (3) Bioelectrical impedance—estimates body composition (less accurate but accessible). (4) Empirical adjustment—track actual weight changes and calorie intake for 4-6 weeks, then calculate actual TDEE backward from results. For most people, standard BMR calculators are "good enough" starting points. Adjust based on real-world results. If eating calculated maintenance but losing weight, actual TDEE is higher—increase calories. If gaining weight, actual TDEE is lower—reduce calories.

Why Use Our BMR Calculator?

Our BMR calculator uses the scientifically validated Mifflin-St Jeor equation, currently considered the gold standard for estimating basal metabolic rate across diverse populations. Unlike older calculators using outdated Harris-Benedict formulas, we provide the most accurate BMR estimates available without clinical testing. The calculator supports both imperial (pounds, feet/inches) and metric (kilograms, centimeters) units for worldwide accessibility, automatically converting between systems for accuracy. Beyond just BMR, we provide activity-adjusted TDEE estimates so you understand your complete daily calorie needs—BMR alone doesn't tell you how much to eat, but TDEE does. The real-time calculation engine delivers instant results as you enter your metrics, with no waiting or button clicking required. Whether you're trying to lose fat, gain muscle, maintain weight, or simply understand your body's energy requirements, our calculator provides the foundational metabolic data you need to create effective nutrition plans. The interface is clean and intuitive, making complex metabolic calculations accessible to everyone from fitness beginners to experienced athletes and nutrition professionals. Best of all, it's completely free, requires no registration, and performs all calculations locally in your browser for complete privacy—your health metrics never leave your device. We've designed this tool to be both accurate and educational, helping you understand not just your BMR number but what it means, how to use it, and how to optimize your metabolism for long-term health and fitness success. Use our calculator as the first step in creating a personalized, science-based nutrition strategy that supports your unique goals and lifestyle.

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