How this is calculated
Methodology
Mifflin-St Jeor equation, the modern standard for resting metabolic rate (more accurate than Harris-Benedict for current populations).
Reviewed by
Calc.Cards Editorial Team
Sources
- 1.Mifflin et al. (1990) A new predictive equation for resting energy expenditure, Am J Clin Nutr
- 2.Academy of Nutrition and Dietetics Evidence Analysis Library (eatright.org)
Your body is constantly burning calories-even right now, while you're sitting. Your heart beats, your lungs breathe, your brain thinks, your organs work. All of that takes energy. Your Basal Metabolic Rate is the total calories your body burns just to exist at rest. It's the foundation of everything else: the larger your BMR, the more you can eat without gaining weight, and the faster you can lose weight in a deficit.
What This Calculator Does
Your BMR calculator computes the calories your body burns at complete rest-no exercise, no movement, just existence. It uses your age, sex, weight, and height to calculate this number through the Mifflin-St Jeor formula, the most accurate and widely used approach. Your BMR typically accounts for 60-75% of your total daily calorie burn. Understanding this baseline gives you insight into your metabolism and how many calories you actually need.
How to Use This Calculator
Enter your age, sex, weight, and height. The calculator instantly displays your BMR in calories per day. You'll also see how this compares to population averages for your age and sex. Understanding your BMR is the first step toward understanding your TDEE (Total Daily Energy Expenditure). Your BMR multiplied by your activity level gives you your TDEE-the number you actually eat to, not your BMR.
The Formula Behind the Math
Your BMR calculator uses the Mifflin-St Jeor formula, developed in 1990 and validated extensively in research:
For Men: (10 × weight kg) + (6.25 × height cm) - (5 × age) + 5
For Women: (10 × weight kg) + (6.25 × height cm) - (5 × age) - 161
This formula is more accurate than older approaches (like Harris-Benedict) because it accounts for the fact that body composition varies-two people at the same weight can have different metabolic rates depending on muscle mass.
Let's work through an example. A 28-year-old man, 75 kg, 175 cm:
This man burns roughly 1,709 calories daily just existing. Add activity on top of that, and his TDEE might be 2,100 calories (sedentary) to 2,800 calories (very active).
For a 28-year-old woman, 65 kg, 165 cm:
Women typically have lower BMR than men at the same weight because of naturally lower muscle mass and higher body fat percentage. This is biological, not a reason for despair-it means being strategic about nutrition and exercise matters more.
Our calculator does all of this instantly-but now you understand exactly what it's computing.
BMR vs. RMR: What's the Difference?
Your Basal Metabolic Rate (BMR) is technically calories burned in a very controlled state (fasted, rested, no recent exercise, temperature controlled). Your Resting Metabolic Rate (RMR) is slightly less controlled-it's just your resting burn. The difference is usually 5-10%, so they're used interchangeably. Both are good proxies for your baseline metabolism.
Factors That Increase Your BMR
Muscle tissue is the biggest factor. Muscle is metabolically active-it burns calories just existing. Building 5 pounds of muscle increases your BMR by roughly 25-50 calories daily. This is why strength training is metabolism-boosting: you're literally creating tissue that burns more energy at rest.
Hormones affect BMR significantly. Thyroid hormones, testosterone, and others regulate metabolism. Medical conditions affecting these hormones change your BMR. This is why some people with thyroid disorders struggle to lose weight-their actual metabolism is lower than predicted.
Genetics matter. Some people naturally have faster metabolisms; others slower. You can't change genetics, but you can change body composition (add muscle) to increase BMR.
Stress and sleep affect BMR. Chronic stress and poor sleep can lower your metabolism slightly. Consistent good sleep and stress management support normal metabolic function.
Why Your BMR Decreases with Age
Metabolism naturally slows roughly 2-8% per decade after age 30, mainly because people lose muscle mass without active resistance training. It's not inevitable-strength training prevents most of this decline. A 50-year-old who weight trains regularly has a higher BMR than a 30-year-old who's sedentary. The key is muscle preservation.
Using Your BMR to Set Calorie Targets
Your BMR is never your daily calorie target (that would be dangerously low unless you're completely immobilized). Instead, multiply your BMR by your activity level:
Your result is your TDEE-the calories you actually eat to maintain weight. This is the foundation of nutrition planning.
Tips and Things to Watch Out For
Your BMR is an estimate, not a precise measurement. The Mifflin-St Jeor formula is accurate within about 10-20% for most people. Your actual BMR depends on factors the formula can't capture: genetics, thyroid function, medications, and more. Use your calculated BMR as a starting point, then monitor your actual results and adjust based on what happens to your weight and energy.
Building muscle is the most reliable way to increase BMR long-term. If you're unhappy with your BMR, the most actionable strategy is strength training. Each pound of muscle increases your BMR by 5-10 calories. Building 10 pounds of muscle increases your daily burn by 50-100 calories-meaningful for weight loss and maintenance.
Don't confuse BMR with how fast you'll lose weight. Your BMR tells you your baseline burn, but fat loss depends on overall deficit. Someone with a 1,500 BMR in a 500-calorie deficit loses weight at the same rate as someone with a 2,000 BMR in a 500-calorie deficit. The deficit matters; the absolute calorie burn doesn't.
Account for the fact that BMR decreases as you lose weight. As your body gets smaller, your BMR decreases. This is normal and expected. If you've been losing weight steadily, your BMR has dropped, so recalculate periodically (every 10-15 pounds). Your maintenance calories have decreased, and you need to adjust accordingly or your weight loss will plateau.
This calculator provides general health information only. Always consult a qualified healthcare provider before making any medical or health decisions.
Frequently Asked Questions
How accurate is the BMR calculator?
The Mifflin-St Jeor formula is accurate within about 10-20% for most people, making it the gold standard for BMR estimation without lab testing. Individual variation exists based on genetics, muscle mass, and hormonal factors. Use your calculated BMR as a starting point, track your results for 2-3 weeks, and adjust based on what actually happens.
Is my BMR the same as my resting metabolic rate?
Essentially, yes. BMR is measured under very controlled conditions (fasted, completely rested); RMR is a practical equivalent measured in normal resting conditions. The difference is 5-10%, so they're used interchangeably. Both represent your baseline metabolism.
Can I increase my BMR?
Yes, through muscle building. Strength training increases muscle mass, which increases your BMR (muscle burns more calories at rest than fat). Hormonal optimization, adequate sleep, and stress management also support normal BMR. However, your genetics set a baseline, and you can't dramatically exceed that.
Does metabolism slow down significantly with age?
Metabolism naturally slows about 2-8% per decade after 30, mainly due to muscle loss (which is preventable through strength training). Someone who weight trains consistently can maintain a high metabolism well into older age. It's not aging itself that slows metabolism-it's inactivity.
Why is my BMR lower than I expected?
Several reasons: the formula is accurate within 10-20%, so your actual might be lower. If you've lost significant weight recently, your BMR has decreased proportionally. If you have a thyroid disorder or take certain medications, your metabolism might be lower than predicted. Discuss this with your doctor if your BMR seems drastically different from your actual results.
Should I eat my BMR or my TDEE calories daily?
Eat your TDEE, not your BMR. Your BMR is baseline; your TDEE includes activity. Eating only your BMR would mean undereating significantly unless you're completely immobilized. Your TDEE is the realistic daily calorie target for weight maintenance.
Related Calculators
Your BMR is the foundation, but your TDEE is what you actually need for nutrition planning. Use the TDEE Calculator to multiply your BMR by your activity level and find your actual daily calorie needs. The Calorie Calculator helps you determine how to adjust calories for weight loss or gain. The Macro Calculator breaks those calories into protein, carbs, and fat. Together, these tools give you complete clarity on your metabolism and nutrition.