BMR Calculator - Basal Metabolic Rate & Daily Calorie Needs Calculator

Mifflin-St Jeor Equation (Recommended)

Developed in 1990, this equation is considered the most accurate for the general population. Men: BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age + 5. Women: BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age - 161. Accuracy within ±10% for most individuals.

Harris-Benedict Equation (Revised)

Originally created in 1919, revised in 1984 for improved accuracy. Men: BMR = 88.362 + 13.397 × weight(kg) + 4.799 × height(cm) - 5.677 × age. Women: BMR = 447.593 + 9.247 × weight(kg) + 3.098 × height(cm) - 4.330 × age. Widely used but slightly less accurate than Mifflin-St Jeor.

Katch-McArdle Formula

Uses lean body mass instead of total weight: BMR = 370 + 21.6 × lean body mass(kg). Most accurate for athletic individuals with known body composition. Requires body fat percentage for calculation. Best choice for muscular individuals or those with accurate body composition data.

Cunningham Equation

Similar to Katch-McArdle but with different coefficients: BMR = 500 + 22 × lean body mass(kg). Often used for highly trained athletes. Provides slightly higher estimates than Katch-McArdle and may be more appropriate for competitive athletes.

Activity Level Multipliers

• Sedentary (1.2): Little to no exercise, desk job, minimal daily activity
• Lightly Active (1.375): Light exercise 1-3 days per week, some walking or recreational activities
• Moderately Active (1.55): Moderate exercise 3-5 days per week, regular gym sessions or sports
• Very Active (1.725): Hard exercise 6-7 days per week, daily training or physical job
• Extremely Active (1.9): Very hard exercise twice per day, intense training, or very physical job

Components of Total Energy Expenditure

TDEE consists of four main components: Basal Metabolic Rate (60-75%), Thermic Effect of Food (8-12%), Exercise Activity Thermogenesis (15-30%), and Non-Exercise Activity Thermogenesis or NEAT (15-20%). Understanding these components helps optimize energy balance for specific goals.

Creating Effective Caloric Deficits

Safe weight loss requires a deficit of 500-1000 calories per day to lose 1-2 pounds weekly. Never eat below your BMR for extended periods, as this can slow metabolism and cause muscle loss. Combine moderate caloric restriction (300-500 calories below TDEE) with increased physical activity for optimal results.

Building Muscle Mass

Muscle gain requires a slight caloric surplus (200-500 calories above TDEE) combined with progressive resistance training. Consume 1.6-2.2g protein per kg body weight to support muscle protein synthesis. Focus on compound movements and gradually increase training volume.

Body Recomposition

Simultaneous fat loss and muscle gain is possible for beginners and those returning to training. Eat at or slightly below TDEE while prioritizing protein intake and consistent strength training. Progress may be slower but results in improved body composition without dramatic weight changes.

Metabolic Adaptation

Extended caloric restriction causes adaptive thermogenesis, reducing BMR by 10-25%. Combat this with periodic diet breaks, resistance training, adequate protein intake, and avoiding excessive deficits. Gradual transitions help maintain metabolic health.

Weight Loss Macros

Protein: 25-35% of calories (1.6-2.4g/kg body weight) to preserve muscle mass and increase satiety. Carbohydrates: 30-40% focused on fiber-rich, nutrient-dense sources. Fats: 25-35% emphasizing essential fatty acids and fat-soluble vitamin absorption.

Muscle Building Macros

Protein: 20-30% of calories (1.6-2.2g/kg body weight) for optimal muscle protein synthesis. Carbohydrates: 40-60% to fuel training and support recovery. Fats: 20-30% for hormone production and overall health. Time protein intake around workouts for maximum benefit.

Athletic Performance

Endurance athletes: Higher carbohydrate intake (6-10g/kg) with moderate protein (1.2-1.4g/kg) and adequate fats (20-25%). Strength athletes: Balanced approach with higher protein (1.6-2.2g/kg), moderate carbs (3-5g/kg), and sufficient fats for hormone production.

Maintenance and Health

Balanced distribution: Protein 15-25%, Carbohydrates 45-65%, Fats 20-35% of total calories. Focus on food quality, adequate fiber intake (25-35g daily), and nutrient timing around physical activity for optimal health and body composition maintenance.

Eating Below BMR

Truth: Consistently eating below BMR can trigger metabolic adaptation, muscle loss, and hormonal disruption. While short-term deficits below BMR may be appropriate in specific circumstances, long-term restriction below this level is counterproductive and potentially harmful.

Overestimating Activity Level

Truth: Most people overestimate their activity level, leading to excessive calorie targets. Be honest about actual exercise frequency and intensity. Formal exercise sessions are only one component of daily energy expenditure.

Ignoring Calorie Quality

Truth: While calories in vs. calories out determines weight change, food quality affects satiety, energy levels, and body composition. Processed foods may have different metabolic effects than whole foods even at identical calorie levels.

Expecting Linear Progress

Truth: Weight loss and muscle gain are not linear processes. Daily fluctuations are normal due to water retention, glycogen stores, and hormonal cycles. Focus on weekly trends rather than daily changes.

One-Size-Fits-All Approach

Truth: BMR calculations are estimates with ±10-15% variability between individuals. Monitor actual results and adjust caloric intake based on progress rather than strictly adhering to calculated values.

Indirect Calorimetry

Gold standard for measuring actual metabolic rate through oxygen consumption and carbon dioxide production. Available at some universities, medical centers, and specialized fitness facilities. Provides precise BMR measurement but requires specialized equipment and professional administration.

Metabolic Testing Devices

Portable indirect calorimeters like BodyGem or MedGem offer convenient BMR testing. Accuracy within 5-10% of laboratory methods when properly calibrated. Useful for baseline measurements and tracking changes over time.

Progress Monitoring Methods

Combine multiple metrics: weekly weight averages, body measurements, progress photos, strength performance, and energy levels. Track for 2-4 weeks before making major adjustments to account for normal fluctuations and adaptation periods.

Adjusting Based on Results

If weight loss stalls after 2-3 weeks, reduce calories by 100-200 or increase activity. If losing weight too rapidly (>2 lbs/week), increase calories by 100-200. For muscle gain, increase calories by 100-300 if no progress after 3-4 weeks.

How accurate are BMR calculator estimates?

BMR calculations are typically accurate within ±10-15% for most people. The Mifflin-St Jeor equation used as our primary method is most accurate for the general population. Individual variations in genetics, body composition, and metabolic efficiency can affect actual BMR.

Should I eat exactly my calculated calories?

Use BMR and TDEE calculations as starting points, then adjust based on actual results over 2-4 weeks. Monitor weight trends, energy levels, and performance to fine-tune your caloric intake. Individual metabolic rates can vary significantly from calculations.

Why is my BMR different from my friend's?

BMR varies based on age, gender, body size, muscle mass, genetics, and health status. Men typically have higher BMR than women due to greater muscle mass. Larger individuals require more energy for basic functions than smaller individuals.

Can I increase my BMR permanently?

Building muscle mass through resistance training is the most effective way to increase BMR long-term. Each pound of muscle burns approximately 6-7 calories daily at rest. Regular exercise, adequate protein, and maintaining healthy body composition help optimize metabolic rate.

How often should I recalculate my BMR?

Recalculate every 10-15 pounds of weight change or every 3-6 months. Significant changes in body composition, training status, or health conditions may also warrant recalculation. Age-related changes occur gradually and don't require frequent adjustments.

Is it safe to eat below my BMR?

Eating below BMR should generally be avoided except under medical supervision. This can trigger metabolic adaptation, muscle loss, hormonal disruption, and nutritional deficiencies. Focus on creating moderate deficits from TDEE instead.

Why do BMR calculators give different results?

Different formulas use varying coefficients and were developed for different populations. Harris-Benedict tends to overestimate slightly, while Mifflin-St Jeor is more conservative. Katch-McArdle accounts for body composition but requires body fat percentage.

Does BMR change with weight loss?

Yes, BMR decreases as body weight decreases due to less tissue requiring energy. Additionally, metabolic adaptation can reduce BMR beyond what weight loss alone would predict. This is why calorie needs must be adjusted during extended weight loss phases.