BMR Calculator - Basal Metabolic Rate

Calculate your Basal Metabolic Rate (BMR) for free with our scientifically accurate calculator. Your BMR represents 60-75% of your total daily energy expenditure and is essential for planning your diet whether you’re looking to lose weight, maintain, or build muscle mass.

What is Basal Metabolic Rate (BMR)?

Basal Metabolic Rate (BMR) is the minimum number of calories your body needs to sustain basic physiological functions at complete rest. This includes breathing, circulation, cell production, nutrient processing, and temperature regulation.

First conceptualized in the 19th century, BMR has become a fundamental tool in nutrition science, sports medicine, and clinical practice.

BMR Calculation Formulas

Several scientifically validated formulas exist to calculate BMR. The most widely used are:

Mifflin-St Jeor Equation (most accurate according to recent studies):

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

Harris-Benedict Equation (classic, revised in 1984):

Men: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age in years)
Women: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age in years)

Katch-McArdle Formula (for those who know their body fat percentage):

BMR = 370 + (21.6 × lean body mass in kg)
Where: Lean body mass = Weight × (1 − body fat %/100)

Practical Example: If you’re a 30-year-old male weighing 165 lbs (75 kg) and 5’9” (175 cm) tall:

BMR = (10 × 75) + (6.25 × 175) − (5 × 30) + 5
BMR = 750 + 1093.75 − 150 + 5
BMR = 1698.75 calories/day

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Factors Affecting Your Basal Metabolic Rate

Your BMR isn’t a fixed number; it’s influenced by multiple factors:

1. Gender

Men typically have a 5-10% higher BMR than women due to greater muscle mass and lower body fat percentage.

2. Age

BMR decreases approximately 2% per decade after age 20, primarily due to gradual loss of muscle mass (sarcopenia).

3. Body Composition

Muscle is metabolically more active than fat tissue. A person with more muscle mass will burn more calories at rest than someone with more body fat, even at the same weight.

4. Genetics

Genetic inheritance can influence your basal metabolic rate by up to 20-30%, though this doesn’t completely determine your metabolism.

5. Climate and Temperature

Living in very cold or very hot climates can slightly increase BMR, as your body needs more energy to regulate its temperature.

6. Hormones

Conditions like hypothyroidism (underactive thyroid) can reduce BMR by 30-40%, while hyperthyroidism can significantly increase it.

7. Pregnancy and Lactation

Pregnancy increases BMR by 20-25% in the third trimester. Breastfeeding increases daily caloric needs by 300-500 calories.

8. Diet History

Very restrictive or prolonged diets can reduce BMR by up to 20% as the body adapts to conserve energy (adaptive thermogenesis).

Activity Levels and Total Daily Energy Expenditure

BMR alone doesn’t represent all the calories you burn daily. To calculate your Total Daily Energy Expenditure (TDEE), multiply your BMR by an activity factor:

Activity Level	Factor	Description
Sedentary	1.2	Little to no exercise, desk job
Lightly Active	1.375	Light exercise 1-3 days/week
Moderately Active	1.55	Moderate exercise 3-5 days/week
Very Active	1.725	Intense exercise 6-7 days/week
Extremely Active	1.9	Very intense daily exercise + physical job

Example: If your BMR is 1700 calories and you’re moderately active:

TDEE = 1700 × 1.55 = 2635 calories/day

How to Use Your BMR to Reach Your Goals

For Weight Loss (Caloric Deficit)

Consume 15-25% fewer calories than your TDEE:

If your TDEE is 2500 kcal, consume 1875-2125 kcal/day
Recommended loss: 1-2 lbs per week
Never go below your BMR to avoid metabolic slowdown

For Muscle Gain (Caloric Surplus)

Consume 10-20% more calories than your TDEE:

If your TDEE is 2500 kcal, consume 2750-3000 kcal/day
Combine with strength training for maximum muscle gain
Recommended gain: 0.5-1 lb per week

For Maintenance

Consume calories equivalent to your TDEE:

Ideal for maintaining current weight
Useful for rest periods between goals

BMR Accuracy and Limitations

Margin of Error

BMR formulas have a margin of error of ±10-15% in the general population because:

They don’t consider individual body composition
They assume standard muscle/fat proportions
They don’t account for specific metabolic conditions

When Standard Formulas May Not Apply

High-performance athletes: Require professional evaluation
People with medical conditions: Diabetes, thyroid disorders, PCOS
Pregnancy and breastfeeding: Significantly increased caloric needs
Children and adolescents: Use age-specific pediatric formulas
Elderly (65+): May have lower accuracy due to muscle loss

How to Increase Your Basal Metabolic Rate

While much of your BMR is genetically determined, you can influence it:

1. Build Muscle Mass

Muscle burns 6 kcal/kg/day, while fat only burns 2 kcal/kg/day
Strength training 2-3 times per week
Progressive overload principle

2. Avoid Extreme Diets

Avoid caloric deficits greater than 25% of your TDEE
Eat at least your BMR daily to prevent metabolic adaptation

3. Consume Adequate Protein

0.7-1 g of protein per lb of body weight (1.6-2.2 g/kg)
Protein has a thermic effect of 20-30% (your body uses more calories to digest it)

4. Stay Active Throughout the Day

NEAT (Non-Exercise Activity Thermogenesis) can account for 300-800 kcal/day
Walk more, take stairs, stand when possible
Fidgeting and small movements add up

5. Get Quality Sleep

7-9 hours of quality sleep
Sleep deprivation can reduce BMR by up to 8%
Poor sleep increases cortisol and reduces muscle recovery

6. Manage Stress

Chronic stress elevates cortisol, which can promote muscle breakdown
Practice stress-reduction techniques

BMR vs RMR: What’s the Difference?

Though often used interchangeably, BMR and RMR are technically different:

BMR (Basal Metabolic Rate): Measured under very strict conditions (12-hour fast, controlled environment, complete rest, upon waking)
RMR (Resting Metabolic Rate): Measured under more relaxed conditions (4-hour fast, simple rest)
RMR is typically 10-15% higher than BMR
For practical purposes, they’re often treated as the same

Professional BMR Measurement Methods

If you need more precise measurement than mathematical formulas, professional methods exist:

Indirect Calorimetry

Measures oxygen consumed and CO₂ produced during rest
Accuracy: ±3-5%
Available at hospitals and specialized sports centers
Cost: $50-150 per session

Direct Calorimetry

Directly measures heat produced by the body
Accuracy: ±1-2%
Very expensive and rarely available (research use only)

Bioelectrical Impedance Analysis (BIA)

Some advanced BIA devices estimate RMR
Accuracy: ±10-20% (less accurate than indirect calorimetry)
More accessible and affordable

Frequently Asked Questions

What’s the difference between BMR and TDEE?

BMR is only the calories burned at rest (vital functions). TDEE (Total Daily Energy Expenditure) includes BMR + physical activity + digestion (thermic effect of food) + thermogenesis.

Which formula is most accurate: Mifflin-St Jeor or Harris-Benedict?

The Mifflin-St Jeor formula is considered 5% more accurate according to recent studies (published 1990 vs 1919/1984 Harris-Benedict). However, if you know your body fat %, Katch-McArdle is even more accurate.

How often should I recalculate my BMR?

Recalculate your BMR whenever:

You lose or gain more than 10 lbs (5 kg)
Your physical activity level changes significantly
Every 6-12 months as a general review

Can I significantly speed up my metabolism?

Supplements and “metabolism-boosting” foods have minimal effects (< 5%). The most effective approach is building muscle mass and maintaining high activity levels.

Why is my BMR different from my friend’s who is the same age and weight?

BMR varies based on body composition, genetics, diet history, hormone levels, and other individual factors. Two people of the same weight can have BMR differences of 20-30%.

Does fasting affect BMR?

Short-term fasting (< 48 hours) has minimal effect. However, prolonged fasting or very low-calorie diets can reduce BMR by 15-20% as an adaptive response.

Can I use BMR to lose weight faster?

Eating significantly below your BMR is counterproductive. It triggers metabolic adaptation (your body slows metabolism to conserve energy), making weight loss harder long-term. Aim for a moderate deficit from TDEE, not BMR.

Scientific References

Mifflin, M.D., et al. (1990). “A new predictive equation for resting energy expenditure in healthy individuals.” American Journal of Clinical Nutrition, 51(2), 241-247.
Harris, J.A., & Benedict, F.G. (1918/1984). “A Biometric Study of Human Basal Metabolism.” Proceedings of the National Academy of Sciences, revised 1984.
Katch, F.I., & McArdle, W.D. (1996). “Nutrition, Weight Control, and Exercise.” Lea & Febiger Publications.
NIH/NHLBI - National Heart, Lung, and Blood Institute. “Calculating Your BMR and Daily Calorie Needs.”
American Council on Exercise (ACE). “Understanding Basal Metabolic Rate.”

Medical Disclaimer: This calculator provides estimates based on standard scientific formulas. For personalized nutritional planning or if you have specific medical conditions, consult with a registered dietitian or certified physician.