BMR Calculator

What Is Basal Metabolic Rate?

Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to stay alive. Breathing. Circulating blood. Producing cells. Regulating body temperature. These functions never stop, and they require energy around the clock. Your BMR is the minimum daily calorie intake needed to sustain them if you were to lie perfectly still for 24 hours.

BMR accounts for 60 to 75% of the calories you burn each day. That is the largest single component of your total energy expenditure. The remaining calories come from physical activity and the thermic effect of food (the energy used to digest what you eat). Once you know your BMR, you multiply it by an activity factor to get your Total Daily Energy Expenditure (TDEE). From there, you eat less than TDEE to lose weight or more to gain. Without knowing your BMR, any calorie target is a guess.

What This Calculator Does

This calculator estimates your BMR using three established formulas and lets you pick the one that fits your situation. It also calculates your TDEE and provides calorie targets for weight loss, maintenance, and weight gain. If you want to go further and break your calorie target into protein, carbs, and fat, pair this with our Macro Calculator.

Inputs Required

• Sex: Biological sex affects which formula coefficients apply
• Age: Metabolic rate declines gradually with age, roughly 1 to 2% per decade
• Height: In feet and inches or centimeters
• Weight: In pounds or kilograms
• Activity Level: How active you are on a typical day, from sedentary to extra active
• Formula: Choose Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle
• Body Fat % (Katch-McArdle only): Required to calculate lean body mass. You can estimate this with our Body Fat Calculator

Outputs Provided

• BMR: Calories burned per day at complete rest
• TDEE: Total calories burned including your activity
• Calorie Targets: Adjusted values for weight loss, maintenance, and weight gain
• Formula Comparison: BMR results from all three formulas side by side

How the Calculation Works

Mifflin-St Jeor Equation (1990)

This is the most widely recommended BMR formula. A 2005 review in the Journal of the American Dietetic Association found it predicted resting metabolic rate more accurately than older equations across most populations. More recent research continues to validate it. A 2025 study published in the American Journal of Physiology-Endocrinology and Metabolism compared multiple prediction models using data from 454 participants and found that simpler models based on standard clinical variables (including the Mifflin-St Jeor approach) performed nearly as well as complex machine learning models. A separate 2025 study on Emirati females found Mifflin-St Jeor was the most accurate of nine tested equations, with 60.1% of predictions falling within 10% of measured RMR.

Harris-Benedict Equation (Revised 1984)

Originally published in 1919 by James Arthur Harris and Francis Gano Benedict, then revised by Roza and Shizgal in 1984, this is one of the oldest BMR formulas still in use. It tends to overestimate BMR slightly compared to Mifflin-St Jeor, particularly in overweight individuals. A 2026 study on perimenopausal women found that Harris-Benedict overestimated resting energy expenditure by an average of 100 calories per day compared to indirect calorimetry, while Mifflin-St Jeor was much closer to measured values.

Katch-McArdle Equation

This formula uses lean body mass instead of total weight. That makes it more accurate for people who know their body fat percentage, especially athletes or those with above-average muscle mass. It does not distinguish between male and female because sex differences are already captured through lean mass. If you do not know your body fat percentage, stick with Mifflin-St Jeor. You can estimate your body fat using our Body Fat Calculator before selecting the Katch-McArdle formula here.

Activity Multipliers (TDEE)

• Sedentary (x1.2): Desk job with little to no exercise. Most office workers fall here.
• Lightly active (x1.375): Light exercise 1 to 3 days per week. Walking, casual cycling, or light yoga.
• Moderately active (x1.55): Moderate exercise 3 to 5 days per week. Gym sessions, running, or sports.
• Very active (x1.725): Hard exercise 6 to 7 days per week. Serious training programs.
• Extra active (x1.9): Very hard daily exercise plus a physical job. Construction workers who also train, for example.

How to Use the Calculator

1. Select imperial or metric units
2. Select your biological sex
3. Enter your age, height, and weight using the sliders
4. If using Katch-McArdle, enter your body fat percentage
5. Select your activity level honestly. Most people overestimate this. When in doubt, pick one level lower than you think
6. Choose your preferred formula. Mifflin-St Jeor is the default and best for most people
7. View your BMR, TDEE, and calorie targets instantly on the right

Example Calculations

Example 1: Moderately Active Male

A 30-year-old male, 5 feet 10 inches (177.8 cm), 170 lbs (77.1 kg), moderately active:

• Mifflin-St Jeor BMR: 10(77.1) + 6.25(177.8) - 5(30) + 5 = 1,737 cal/day
• Activity factor (x1.55): 1,737 x 1.55 = 2,692 cal/day (TDEE)
• Weight loss target: 2,692 - 500 = 2,192 cal/day (roughly 1 lb/week loss)
• Weight gain target: 2,692 + 500 = 3,192 cal/day (roughly 1 lb/week gain)

Example 2: Sedentary Female Using Katch-McArdle

A 45-year-old female, 5 feet 4 inches (162.6 cm), 155 lbs (70.3 kg), 28% body fat, sedentary:

• Lean body mass: 70.3 x (1 - 0.28) = 50.6 kg
• Katch-McArdle BMR: 370 + 21.6(50.6) = 1,463 cal/day
• Activity factor (x1.2): 1,463 x 1.2 = 1,756 cal/day (TDEE)
• Weight loss target: 1,756 - 500 = 1,256 cal/day

Note that 1,256 calories is quite low. For many women, a 500-calorie deficit from a sedentary TDEE can be aggressive. A smaller deficit of 250 calories (eating 1,506 cal/day) would produce slower but more sustainable fat loss of about 0.5 lbs per week. You can also check your BMI to see where your current weight falls on the standard scale.

Real-World Scenarios

Starting a Weight Loss Plan Without Guessing

Sarah, a 38-year-old marketing manager in Chicago, has been trying to lose 20 lbs for a year with no success. She has been eating 1,500 calories per day based on a generic app recommendation. She enters her details into the BMR calculator and discovers her TDEE is 1,950 calories at her actual activity level (sedentary, not "lightly active" as she had been telling the app). Her 1,500-calorie target is only a 450-calorie deficit, which should produce slow loss. But on weekends she eats closer to 2,200, wiping out the weekday deficit. She switches to a consistent 1,450 calories daily and loses 1 lb per week for the next 12 weeks.

Lean Bulk for a Competitive Cyclist

Miguel, a 27-year-old competitive cyclist in Boulder, Colorado, wants to gain 5 lbs of muscle during his off-season. He is 5 feet 11 inches, 165 lbs, with 10% body fat measured by calipers. Using Katch-McArdle, his BMR is 1,748. With a very active multiplier (x1.725), his TDEE is 3,015. He adds 300 calories for a lean bulk, eating 3,315 calories daily. He tracks his weight weekly and adjusts by 100 calories if the scale moves more than 0.5 lbs per week in either direction. Over 16 weeks, he gains 4.8 lbs with minimal fat gain, confirmed by a follow-up body fat measurement.

Adjusting Calories After Menopause

Linda, a 54-year-old woman entering perimenopause, notices she is gaining weight despite eating the same amount she always has. She calculates her BMR and finds it has dropped to 1,320 calories, about 80 calories lower than five years ago due to age-related muscle loss and hormonal changes. Her TDEE at lightly active is 1,815. She was eating 1,900 calories, a slight surplus. She reduces to 1,600 and starts resistance training twice weekly to preserve muscle mass. After 8 weeks, her weight stabilizes. A 2026 study in the Journal of the American Nutrition Association confirmed that Mifflin-St Jeor is the most accurate predictive equation for perimenopausal women, overestimating by only 18.5 calories on average compared to indirect calorimetry.

Why This Calculation Matters

Without knowing your BMR and TDEE, any calorie target you set is essentially a guess. BMR is the baseline that makes personalized nutrition planning possible. Whether you are trying to lose fat, build muscle, improve athletic performance, or simply maintain a healthy weight, your BMR is the number that makes the rest of the math work.

BMR also changes over time. As you lose weight, gain muscle, or age, your BMR shifts. A 2025 study in the American Journal of Clinical Nutrition developed new equations specifically for adults over 65, finding that standard formulas like Mifflin-St Jeor lose accuracy in older populations due to sarcopenia (age-related muscle loss). Recalculating your BMR every 2 to 3 months while actively dieting or training keeps your targets aligned with your actual metabolic needs. For a complete picture of your daily energy expenditure, you can also use our TDEE Calculator.

Common Mistakes to Avoid

• Confusing BMR with TDEE: BMR is calories at complete rest. TDEE is your actual daily burn including movement. You should eat near your TDEE to maintain weight, not your BMR. Eating at BMR would be a severe deficit for anyone who is not bedridden
• Overestimating activity level: Most people overestimate how active they are. This is the most common cause of a stalled diet. If you work a desk job and go to the gym 3 times a week, you are lightly active, not moderately active. When uncertain, choose one level lower than you think
• Not recalculating after weight changes: Every 10 to 15 lbs of weight change will shift your BMR meaningfully. If you lose 20 lbs and do not recalculate, you may be eating at maintenance when you think you are in a deficit
• Treating the result as exact: BMR formulas estimate a population average. Individual metabolism can vary by 10 to 15%. A 2025 study using machine learning on 454 participants found that even the best models explained only about 77% of RMR variance. Adjust your intake based on real-world results over 2 to 3 weeks, not just the calculator output
• Ignoring the thermic effect of food: TDEE includes activity but the thermic effect of food (TEF) accounts for roughly 10% of total energy expenditure. Protein has the highest TEF at 20 to 30%, meaning 100 calories of protein yields only 70 to 80 usable calories. This is why high-protein diets can produce slightly more fat loss than isocaloric diets

Limitations of This Calculator

BMR formulas estimate population averages, not individual values. The only way to measure your true BMR is through indirect calorimetry, which requires clinical equipment. This calculator provides a well-validated estimate that is accurate for most people within 10 to 15%. It does not account for medical conditions that affect metabolism (hypothyroidism, PCOS, Cushing's syndrome), medications that alter metabolic rate, or pregnancy. If you have a metabolic condition, consult a registered dietitian or physician for personalized guidance.

Authoritative Research and Resources

• Mifflin-St Jeor Original Paper (American Journal of Clinical Nutrition, 1990) - The original publication introducing the Mifflin-St Jeor equation, developed from a study of 498 healthy adults. This is the foundational paper for the most widely recommended BMR formula in use today.
• Predicting Resting Metabolic Rate in Healthy Adults (American Journal of Physiology, 2025) - A 2025 study that compared traditional prediction equations with machine learning models using data from 454 participants. Found that fat-free mass, body weight, and even outdoor temperature are key predictors, and that simpler models perform nearly as well as complex ones.
• Physiology, Body Mass Index - StatPearls (NCBI) - A peer-reviewed reference from the National Library of Medicine that covers metabolic rate, body composition, and the clinical significance of energy expenditure measurements. Useful for understanding how BMR relates to overall health assessment.