BMR Calculator - Basal Metabolic Rate
Calculate your basal metabolic rate using multiple validated scientific formulas including Mifflin-St Jeor, Harris-Benedict, Katch-McArdle, and more
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Mifflin–St Jeor is a common default for healthy adults when height, weight, and age are known. Katch–McArdle and Cunningham use lean mass when you supply body fat or LBM—helpful for trained athletes. Pair BMR with an activity factor (TDEE) for daily targets; discuss chronic conditions with a clinician or dietitian.
Ready to run the numbers?
Why: Basal metabolic rate (BMR) is the energy your body needs at complete rest to run organs, circulation, and basic cell work. Comparing several published equations helps you choose a reasonable calorie baseline before adding activity.
How: Enter anthropometrics and optional body-composition fields. The tool runs multiple BMR formulas in parallel, highlights a recommended blend, and shows how lean mass and age shift the estimate—always treat output as educational, not a medical prescription.
Run the calculator when you are ready.
🏃 Young Male Athlete
25-year-old athletic male with low body fat seeking metabolic optimization
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👩 Middle-Aged Woman
45-year-old woman with moderate activity seeking weight management
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👴 Active Senior
65-year-old male focused on maintaining healthy metabolism
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💪 Bodybuilder
30-year-old competitive bodybuilder with high muscle mass
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👩🦳 Post-Menopausal Woman
55-year-old woman experiencing metabolic changes
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For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
Understanding Basal Metabolic Rate
Basal Metabolic Rate (BMR) represents the minimum energy your body needs to maintain vital functions at rest. Understanding your BMR is the foundation of effective nutrition planning, weight management, and metabolic health optimization.
Key Takeaways
- ✓BMR accounts for the majority (60-75%) of total daily energy expenditure in most people.
- ✓The Mifflin-St Jeor equation is the current gold standard recommended by the Academy of Nutrition and Dietetics.
- ✓Lean body mass is the strongest predictor of BMR, which is why body composition matters more than weight alone.
- ✓Severe calorie restriction can decrease BMR by 10-20% through adaptive thermogenesis.
Did You Know?
Your brain alone consumes about 20% of your BMR despite being only 2% of your body weight.
The liver is the most metabolically active organ, consuming about 27% of resting energy expenditure.
BMR is highest in the morning and lowest during sleep, varying by about 5-10% throughout the day.
Identical twins have BMRs within 5% of each other, suggesting a strong genetic component to metabolism.
Cold exposure can temporarily increase BMR by activating brown adipose tissue for heat generation.
Caffeine can increase BMR by 3-11% for several hours after consumption by stimulating the nervous system.
How Does Basal Metabolic Rate Work?
Mifflin-St Jeor Equation
The gold standard formula uses weight (kg), height (cm), age, and sex. For men: 10W + 6.25H - 5A + 5. For women: 10W + 6.25H - 5A - 161. It was validated in 2005 as the most accurate for diverse populations.
Harris-Benedict Equation
The classic 1918 formula (revised 1984) uses similar variables but different coefficients. It tends to overestimate BMR by 5-15% in overweight individuals, which is why Mifflin-St Jeor is now preferred.
Katch-McArdle Formula
This formula uses lean body mass (LBM) instead of total weight: BMR = 370 + 21.6 x LBM(kg). It is the most accurate when body fat percentage is known, as it directly accounts for metabolically active tissue.
Expert Tips
Know Your Body Composition
Get a body fat percentage measurement for the most accurate BMR calculation using the Katch-McArdle formula.
Use Activity Multipliers
Multiply your BMR by 1.2 (sedentary) to 1.9 (very active) to estimate your actual daily calorie needs.
Recalculate Regularly
Update your BMR calculation every 10-15 pounds of weight change or every 3 months to stay on track.
Protect Your Metabolism
Never consistently eat below your BMR. Chronic under-eating triggers metabolic adaptation that lowers your metabolic rate.
Basal Metabolic Rate Comparison
| Formula | Best For | Variables | Accuracy |
|---|---|---|---|
| Mifflin-St Jeor | Most adults | Weight, Height, Age, Sex | ±10% for 82% |
| Harris-Benedict | Normal weight | Weight, Height, Age, Sex | ±10% for 75% |
| Katch-McArdle | Athletes/known BF% | Lean Body Mass | ±10% for 85% |
| Cunningham | Athletes | Fat-Free Mass | ±10% for 80% |
Frequently Asked Questions
What is Basal Metabolic Rate (BMR)?
BMR is the number of calories your body burns at complete rest to maintain basic life functions like breathing, circulation, and cell production. It accounts for 60-75% of your total daily energy expenditure and is the foundation for calculating calorie needs.
Which BMR formula is most accurate?
The Mifflin-St Jeor equation is considered the most accurate for most adults, with an accuracy within 10% for 82% of people. The Katch-McArdle formula is preferred when body fat percentage is known, as it accounts for lean body mass.
How is BMR different from TDEE?
BMR measures calories burned at absolute rest, while TDEE (Total Daily Energy Expenditure) includes all daily activity. TDEE equals BMR multiplied by an activity factor (1.2 for sedentary to 1.9 for extremely active individuals).
Does muscle mass affect BMR?
Yes, muscle tissue is metabolically more active than fat tissue, burning approximately 6 calories per pound per day compared to 2 for fat. This is why strength training can increase BMR by building lean muscle mass.
Does BMR change with age?
BMR typically decreases by about 1-2% per decade after age 20, primarily due to loss of lean muscle mass (sarcopenia). Regular resistance training can help slow this decline and maintain a higher metabolic rate.
Can you increase your BMR?
Yes, through building muscle mass via resistance training, increasing NEAT (non-exercise activity), eating adequate protein (which has a high thermic effect), getting sufficient sleep, and avoiding very low calorie diets that trigger metabolic adaptation.
Key Statistics
Official Data Sources
Medical Disclaimer
This calculator is for educational and informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before making health decisions based on calculator results.
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