BMR Calculator
Calculate your Basal Metabolic Rate and daily calorie needs based on your activity level. Free, instant, and private.
What This Tool Does
Three Proven Formulas
Choose from Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle equations. Each formula serves a different use case, from general estimates to body-composition-aware calculations for athletes and fitness enthusiasts.
Activity-Level TDEE
Go beyond your resting rate. See your estimated Total Daily Energy Expenditure across five activity levels, from sedentary desk workers to elite athletes training multiple times per day.
Metric & Imperial Units
Enter your height in centimeters or feet and inches, and your weight in kilograms or pounds. Toggle freely between unit systems without losing your data. All conversions happen automatically in the background.
Instant & Private
All calculations run entirely in your browser. No data is sent to any server, no account is required, and there is nothing to install. Get your results in milliseconds with complete privacy.
Using BMR Calculator in 4 Steps
- Select your gender — Choose Male or Female. This matters because men and women have different metabolic rates due to differences in body composition and hormonal profiles.
- Enter your age, height, and weight — Provide your current age in years, height in centimeters or feet and inches, and weight in kilograms or pounds. You can toggle between metric and imperial units at any time.
- Choose a formula — Mifflin-St Jeor is recommended for most people. If you know your body fat percentage, Katch-McArdle may give a more accurate result for lean or athletic builds.
- Click Calculate BMR — Your basal metabolic rate will appear along with a full table showing estimated daily calorie needs for five different activity levels, from sedentary to extra active.
Your BMR accounts for 60-75% of total daily energy expenditure. The remaining 25-40% comes from physical activity (15-30%) and the thermic effect of food (about 10%). Crash diets that drastically cut calories can lower your BMR, making weight loss harder over time.
Confusing BMR with TDEE. BMR is the energy your body needs at complete rest — just to keep organs functioning. Your total daily energy expenditure (TDEE) multiplies BMR by an activity factor. Eating at your BMR level when you are physically active creates too large a deficit.
Understanding Basal Metabolic Rate (BMR)
Basal Metabolic Rate, commonly known as BMR, is the total number of calories your body requires to perform its most fundamental biological functions while at complete rest. These functions include breathing, blood circulation, cell repair and growth, brain and nerve function, and maintaining body temperature. Your BMR accounts for the largest portion of your total daily calorie expenditure, typically representing 60 to 75 percent of the calories you burn every single day. Understanding your BMR is the foundation of any effective weight management or nutrition strategy because it tells you the absolute minimum number of calories your body needs to survive and function properly.
Several factors influence your BMR. Body size and composition play the most significant role: larger bodies and those with greater muscle mass burn more calories at rest. Age is another critical factor, as metabolic rate naturally decreases by approximately one to two percent per decade after the age of twenty, primarily due to the gradual loss of lean muscle tissue. Gender also matters because men generally have higher BMR than women due to having more muscle mass and less body fat. Genetics, hormonal levels, and even environmental temperature can affect your resting metabolic rate to varying degrees.
BMR vs. TDEE: What Is the Difference?
While BMR measures the calories your body burns at complete rest, Total Daily Energy Expenditure (TDEE) represents the total number of calories you burn throughout an entire day including all physical activities. TDEE is calculated by multiplying your BMR by an activity factor that corresponds to your lifestyle and exercise habits. A sedentary person who works a desk job and does little exercise would multiply their BMR by 1.2, while an extremely active athlete might use a multiplier of 1.9. Your TDEE is the number that truly matters when setting calorie intake goals for weight loss, maintenance, or muscle gain. To lose weight, you need to consume fewer calories than your TDEE. To gain weight or build muscle, you need to eat more than your TDEE.
Comparing the BMR Formulas
The Mifflin-St Jeor equation, published in 1990, is considered the most reliable formula for estimating BMR in the general population and is recommended by the Academy of Nutrition and Dietetics. It uses weight, height, age, and gender as inputs and has been shown to predict resting metabolic rate within ten percent of measured values for most individuals. The Harris-Benedict equation is older, originally published in 1919 and later revised in 1984 by Roza and Shizgal. While it is still widely used and reasonably accurate, studies have found that it tends to overestimate BMR by about five percent compared to indirect calorimetry measurements. The Katch-McArdle formula takes a fundamentally different approach by using lean body mass instead of total weight, making it potentially more accurate for athletes and individuals who know their body fat percentage. Because it factors out body fat, it provides a single equation used for both men and women.
Why BMR Matters for Weight Management
Knowing your BMR is essential for creating an effective and sustainable nutrition plan. If you are trying to lose weight, eating below your TDEE but above your BMR ensures that your body gets enough fuel to function properly while still creating a calorie deficit. Eating significantly below your BMR for extended periods can trigger metabolic adaptation, where your body slows its metabolism to conserve energy, making further weight loss increasingly difficult. For those looking to build muscle, understanding your BMR helps you determine how many additional calories you need to support muscle protein synthesis without excessive fat gain. Even for weight maintenance, knowing your BMR helps you make informed decisions about portion sizes, meal frequency, and how to adjust your intake when your activity levels change. Whether your goal is losing fat, building lean muscle, or simply maintaining a healthy body composition, your BMR serves as the starting point for all calorie calculations.
Questions & Answers
What is Basal Metabolic Rate (BMR)?
Basal Metabolic Rate is the number of calories your body needs to carry out essential life-sustaining processes while completely at rest. These processes include breathing, pumping blood through your circulatory system, regulating body temperature, producing hormones, repairing cells, and maintaining brain function. Your BMR is measured under very restrictive conditions: a subject must be fully rested, in a fasting state of at least twelve hours, lying down in a thermally neutral environment. For most adults, BMR typically ranges between 1,200 and 2,400 calories per day, depending on body size, age, gender, and body composition.
How is BMR different from TDEE?
BMR measures only the calories your body burns at complete rest to keep you alive, while TDEE (Total Daily Energy Expenditure) includes all the calories you burn throughout the day from every source: your BMR, physical activity, exercise, the thermic effect of food (calories burned during digestion), and non-exercise activity thermogenesis (NEAT, such as fidgeting, walking, and household tasks). TDEE is always higher than BMR. To calculate TDEE, your BMR is multiplied by an activity factor ranging from 1.2 for sedentary lifestyles to 1.9 for people with very demanding physical routines. TDEE is the more practical number for planning your daily caloric intake.
Which BMR formula is the most accurate?
The Mifflin-St Jeor equation is widely regarded as the most accurate BMR formula for the general adult population. A study published in the Journal of the American Dietetic Association compared several predictive equations against indirect calorimetry and found Mifflin-St Jeor to be the best predictor across normal weight, overweight, and obese groups. However, the Katch-McArdle formula may be more accurate for individuals who have a reliable measurement of their body fat percentage, especially lean athletes. The Harris-Benedict equation, while historically significant and still commonly used, has been shown to slightly overestimate BMR in several studies.
How can I increase my BMR?
The most effective way to increase your BMR is to build lean muscle mass through resistance and strength training. Muscle tissue is metabolically more active than fat tissue, burning roughly six to seven calories per pound per day at rest compared to about two calories per pound for fat. Other strategies include staying well-hydrated, eating adequate protein to support muscle maintenance and the thermic effect of food, getting seven to nine hours of quality sleep each night, and avoiding prolonged very-low-calorie diets that can trigger metabolic adaptation. High-intensity interval training (HIIT) has also been shown to temporarily elevate metabolic rate for hours after exercise, a phenomenon known as excess post-exercise oxygen consumption (EPOC).
Does age affect BMR?
Yes, BMR decreases naturally with age. After around age twenty, most people experience a decline in BMR of approximately one to two percent per decade. This is primarily caused by the gradual loss of lean muscle mass, a process known as sarcopenia, as well as hormonal changes including decreasing levels of growth hormone and testosterone. By age seventy, an individual's BMR may be ten to twenty percent lower than it was at age twenty-five. This age-related metabolic decline is one of the main reasons why many people find it easier to gain weight as they get older, even without significant changes in eating habits.
Why is BMR different for men and women?
Men typically have a higher BMR than women of similar age and body size. This difference is primarily due to body composition: men generally carry more lean muscle mass and have a lower body fat percentage than women. Hormonal differences also play a role, as testosterone promotes the development and maintenance of muscle tissue. On average, a man's BMR is about five to ten percent higher than that of a woman with comparable height, weight, and age. This is why the Mifflin-St Jeor and Harris-Benedict equations include separate formulas for men and women, while the Katch-McArdle equation uses a single formula based on lean body mass, which inherently accounts for gender differences in body composition.
Should I eat below my BMR to lose weight?
While eating below your BMR will create a calorie deficit that leads to weight loss, most nutrition experts do not recommend sustained calorie intake below your BMR. Consuming fewer calories than your body needs for its most basic functions can lead to muscle loss, nutritional deficiencies, fatigue, hormonal disruption, and metabolic adaptation where your body lowers its metabolic rate to conserve energy. Instead, the recommended approach is to eat between your BMR and TDEE, creating a moderate deficit of about 500 to 750 calories below your TDEE. This approach promotes gradual, sustainable weight loss of one to one-and-a-half pounds per week while preserving muscle mass and supporting essential body functions.
BMR Formulas Compared
Several equations exist for estimating Basal Metabolic Rate. Each was developed from different study populations and uses slightly different variables. Understanding their differences helps you choose the most appropriate formula for your situation and interpret your results with the right context.
- Harris-Benedict Equation (Revised 1984)
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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)
Originally published in 1919 and revised by Roza and Shizgal in 1984. This is one of the oldest and most widely referenced BMR formulas. It tends to overestimate calorie needs by 5 to 15 percent in overweight and obese individuals because it was derived from a study population that was predominantly lean.
- Mifflin-St Jeor Equation (1990)
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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
Developed by Mifflin and St Jeor in 1990 using a more modern and diverse study sample. The American Dietetic Association considers this the most accurate formula for most adults. It provides reliable estimates for people across a wider range of body weights and is the default recommendation for clinical use when body fat percentage is unknown.
- Katch-McArdle Formula
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Both sexes: BMR = 370 + (21.6 × lean body mass in kg)
Unlike the other formulas, Katch-McArdle uses lean body mass (fat-free mass) rather than total weight, height, age, and sex. This makes it the most accurate option for individuals who know their body fat percentage, especially athletes and very lean or very overweight individuals. Because it factors out fat tissue, it avoids the overestimation problem that affects weight-based equations in obese populations.
Which should you use? If you do not know your body fat percentage, the Mifflin-St Jeor equation is the most reliable general-purpose choice. If you have had your body fat measured via DEXA scan, hydrostatic weighing, or calipers, the Katch-McArdle formula will give you the most personalized result. Regardless of which formula you use, treat the output as an estimate and adjust based on real-world results over two to four weeks.
Disclaimer: BMR calculations are estimates. Actual metabolic rate is influenced by genetics, hormones, medications, and other factors. Consult a healthcare professional for clinical guidance.