BMR Calculator

Your Basal Metabolic Rate (BMR) is the number of calories your body burns every day just to stay alive.

Reviewed by: CalcMojo Editorial Team

Breathing, circulating blood, regulating body temperature, repairing cells, and maintaining organ function all require energy, and that baseline energy cost is your BMR. For most people, BMR accounts for 60% to 75% of total daily calorie expenditure, making it by far the largest component of your energy budget.

This BMR calculator uses the Mifflin-St Jeor equation, which the American Dietetic Association identified as the most accurate predictive equation for estimating resting metabolic rate in healthy adults. Enter your age, sex, height, and weight, and the tool returns your estimated BMR in calories per day. The calculator also shows results from the Harris-Benedict equation and the Katch-McArdle formula for comparison.

Understanding your BMR is the first step toward setting an accurate calorie target for any goal, whether that is weight loss, maintenance, or muscle gain. Your BMR tells you the absolute floor below which you should not eat without medical supervision. From there, adding your activity level produces your Total Daily Energy Expenditure (TDEE), which is the number you actually use for meal planning. Use this tool alongside our TDEE Calculator to get the complete picture.

What Is Basal Metabolic Rate?

Basal Metabolic Rate is the rate at which your body expends energy at complete physiological rest. Technically, BMR is measured under strict laboratory conditions: the subject must be in a post-absorptive state (12 hours of fasting), lying down in a thermoneutral environment, having slept for at least 8 hours, and free from physical or psychological stress. Under these conditions, the only energy being expended is what is required to maintain basic life functions.

In clinical practice, Resting Metabolic Rate (RMR) is more commonly measured because the conditions are less restrictive. RMR is typically 10% to 20% higher than true BMR because the subject is awake and not required to fast as long. Most online calculators, including this one, technically estimate RMR using predictive equations but use the term BMR because it is more widely recognized by the general public.

Your BMR is influenced by several factors:

Lean body mass. Muscle tissue is metabolically active and burns more calories at rest than fat tissue. People with more lean mass have higher BMRs, which is one reason men typically have higher BMRs than women of the same height and weight.

Age. BMR declines approximately 1% to 2% per decade after age 20, primarily due to the gradual loss of lean mass (sarcopenia) that occurs with aging. A 50-year-old will have a lower BMR than a 25-year-old of the same size and body composition.

Sex. Men generally have 10% to 15% higher BMRs than women of similar size, due to differences in body composition, hormonal profiles, and organ size.

Body size. Larger bodies require more energy to maintain. A person who weighs 200 pounds has a higher BMR than a person who weighs 140 pounds, even if both have the same body fat percentage.

Genetics. Individual variation in metabolic rate can range by 200-300 calories per day even among people of similar size, age, and body composition. This genetic component is real but is often exaggerated as an excuse for weight gain.

The Mifflin-St Jeor Equation

The Mifflin-St Jeor equation was published in 1990 and has become the gold standard for BMR estimation in clinical nutrition:

For men: BMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) + 5

For women: BMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) – 161

A 2005 systematic review by the American Dietetic Association compared the Mifflin-St Jeor equation against the Harris-Benedict, Owen, and WHO/FAO/UNU equations and concluded that Mifflin-St Jeor was the most reliable predictor of measured resting metabolic rate across a range of body weights, predicting within 10% of measured values for the majority of healthy, non-obese adults.

Other BMR Equations

Harris-Benedict Equation (Revised 1984). Originally published in 1919 by James Arthur Harris and Francis Gano Benedict, this was the most widely used equation for decades. The revised version by Roza and Shizgal (1984) improved accuracy:

  • Men: BMR = (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age) + 88.362
  • Women: BMR = (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age) + 447.593

The Harris-Benedict equation tends to overestimate BMR by 5% to 15% compared to measured values, particularly in overweight and obese individuals.

Katch-McArdle Formula. This equation uses lean body mass instead of total weight, making it potentially more accurate for people who know their body fat percentage:

BMR = 370 + (21.6 x lean body mass in kg)

Because it accounts for body composition directly, the Katch-McArdle formula can be more accurate for athletes and very lean individuals. However, it requires an accurate body fat measurement, which most people do not have. Use our Body Fat Calculator to estimate your body fat percentage, then apply it here.

BMR vs TDEE: Understanding the Difference

BMR and TDEE are related but fundamentally different numbers, and confusing them is one of the most common mistakes in nutrition planning.

BMR is the calories your body burns at complete rest. It is the energy cost of simply existing. You would burn this many calories even if you stayed in bed for 24 hours straight.

TDEE is your BMR plus all additional calories burned through daily activity, exercise, and food digestion. TDEE is always higher than BMR and is the number you should use when setting calorie targets for weight loss, maintenance, or gain.

For a sedentary person, TDEE is typically about 20% higher than BMR (BMR x 1.2). For a very active person, TDEE can be 70% to 90% higher than BMR (BMR x 1.725 to 1.9).

Why the distinction matters: If your BMR is 1,600 calories and you eat 1,600 calories thinking it is your maintenance level, you are actually in a significant calorie deficit because your TDEE, accounting for even minimal daily activity, is closer to 1,920 calories or more. Conversely, if your TDEE is 2,400 calories and you mistake your BMR of 1,800 as your total burn, you might eat 2,200 calories thinking you are in a deficit when you are actually quite close to maintenance.

Use our TDEE Calculator to convert your BMR into an actionable TDEE based on your actual activity level.

Factors That Increase or Decrease BMR

Understanding what raises or lowers your BMR can help you make informed decisions about your metabolism.

Factors that increase BMR:

  • Building lean muscle mass through resistance training
  • Higher protein intake (protein has a higher thermic effect)
  • Cold exposure (the body burns extra calories to maintain core temperature)
  • Stimulants like caffeine (modest, temporary effect of 3-11%)
  • Pregnancy and lactation
  • Fever and illness (metabolic rate increases roughly 7% per degree Fahrenheit above normal)

Factors that decrease BMR:

  • Prolonged calorie restriction (metabolic adaptation)
  • Loss of lean muscle mass
  • Aging
  • Hormonal conditions such as hypothyroidism
  • Extended periods of inactivity
  • Crash dieting and very low calorie diets

Metabolic adaptation deserves special attention. When you eat in a calorie deficit for an extended period, your body reduces its metabolic rate beyond what would be predicted by the weight loss alone. This is a survival mechanism, but it means that after months of dieting, your actual BMR may be lower than what this calculator predicts. Periodic diet breaks at maintenance calories (1-2 weeks at TDEE) can help mitigate metabolic adaptation.

How to Use Your BMR for Nutrition Planning

Your BMR provides the foundation for building a calorie plan:

Step 1: Calculate your BMR using this calculator.

Step 2: Determine your TDEE by multiplying your BMR by the appropriate activity factor using our TDEE Calculator.

Step 3: Set your calorie target based on your goal. For weight loss, eat 250-500 calories below TDEE. For maintenance, eat at TDEE. For muscle gain, eat 200-400 calories above TDEE.

Step 4: Break your calories into macronutrients using our Macro Calculator to ensure adequate protein, carbohydrate, and fat intake.

Step 5: Monitor and adjust. Track your weight weekly and compare to predictions. If results diverge from expectations after 2-3 weeks, adjust your calorie target by 100-200 calories.

Never eat below your BMR for extended periods without medical supervision. Eating below BMR means consuming fewer calories than your body needs just for basic physiological functions, which can lead to nutrient deficiencies, muscle loss, hormonal disruption, and metabolic damage.

This calculator provides general estimates based on published formulas. It is not medical advice and does not replace consultation with a qualified healthcare provider.

Frequently Asked Questions

What is a normal BMR?

BMR varies widely based on age, sex, height, weight, and body composition. For adult women, typical BMR ranges from 1,200 to 1,600 calories per day. For adult men, typical BMR ranges from 1,400 to 1,800 calories per day. Athletes and larger individuals may have BMRs above 2,000.

What is the difference between BMR and RMR?

BMR (Basal Metabolic Rate) is measured under strict laboratory conditions after 12 hours of fasting and complete rest. RMR (Resting Metabolic Rate) is measured under less restrictive conditions and is typically 10% to 20% higher than true BMR. Most online calculators, including this one, estimate RMR but use the term BMR because it is more widely recognized.

Which BMR equation is the most accurate?

The Mifflin-St Jeor equation is considered the most accurate for healthy adults, according to a 2005 review by the American Dietetic Association. It predicts measured metabolic rate within 10% for most people. The Katch-McArdle formula may be more accurate if you have a reliable body fat measurement.

Can I increase my BMR?

The most effective way to increase BMR is to build lean muscle mass through resistance training. Each pound of muscle burns approximately 6 calories per day at rest, compared to about 2 calories per pound of fat. While this difference seems small per pound, adding 10-15 pounds of muscle can increase daily calorie burn by 40-90 calories.

Should I eat below my BMR to lose weight?

Eating below your BMR for extended periods is generally not recommended without medical supervision. Your BMR represents the minimum energy your body needs for basic life functions. Chronic under-eating at this level can cause muscle loss, hormonal disruption, nutrient deficiencies, and metabolic adaptation. Instead, eat below your TDEE but above your BMR for safe, sustainable weight loss.

Why does BMR decrease with age?

BMR declines approximately 1% to 2% per decade after age 20, primarily because of the gradual loss of metabolically active lean muscle mass that occurs with aging. Hormonal changes, including declining levels of growth hormone and testosterone, also contribute. Regular resistance training can slow this decline significantly.

How does body composition affect BMR?

Body composition is one of the strongest determinants of BMR. Lean muscle tissue is metabolically active and requires more energy to maintain than fat tissue. Two people of the same height, weight, age, and sex can have BMRs that differ by several hundred calories if one has significantly more muscle mass. This is why the Katch-McArdle formula, which uses lean body mass, can be more accurate than weight-based equations.

Sources & Methodology

  • Primary BMR equation: Mifflin MD, St Jeor ST, et al., "A new predictive equation for resting energy expenditure in healthy individuals," American Journal of Clinical Nutrition, 1990.
  • Harris-Benedict revision: Roza AM, Shizgal HM, "The Harris Benedict equation reevaluated," American Journal of Clinical Nutrition, 1984.
  • Katch-McArdle formula from McArdle WD, Katch FI, Katch VL, "Exercise Physiology: Energy, Nutrition, and Human Performance," 2006.
  • Equation accuracy comparison: Frankenfield DC, Roth-Yousey L, Compher C, "Comparison of Predictive Equations for Resting Metabolic Rate," Journal of the American Dietetic Association, 2005.
  • Metabolic adaptation data from Rosenbaum M, Leibel RL, "Adaptive thermogenesis in humans," International Journal of Obesity, 2010.

Default values shown are illustrative. Always verify with your healthcare provider. Data accurate as of: March 2026