BMR Calculator
Calculate your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation. BMR is the number of calories your body burns at rest to maintain basic life functions.
Estimated Daily Calories by Activity Level
Your Total Daily Energy Expenditure (TDEE) depends on how active you are.
| Activity Level | Description | Calories/Day |
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Understanding Basal Metabolic Rate (BMR)
Your Basal Metabolic Rate is the number of calories your body requires each day to maintain essential physiological functions while at complete rest. These functions include breathing, circulating blood, regulating body temperature, cell production, and brain activity. BMR typically accounts for 60 to 75 percent of total daily calorie expenditure, making it the single largest component of your energy budget. Knowing your BMR provides a scientific foundation for setting caloric intake goals, whether you are trying to lose weight, gain muscle, or simply maintain your current body composition.
Mifflin-St Jeor vs. Harris-Benedict Equations
Two formulas have dominated BMR estimation for decades. The Harris-Benedict equation, originally published in 1919 and revised in 1984, was the standard for most of the twentieth century. It calculates BMR using weight, height, age, and gender, but studies have shown that it tends to overestimate caloric needs by about 5 percent in many individuals. The Mifflin-St Jeor equation, introduced in 1990, uses the same input variables but produces results that more closely match measured metabolic rates in modern populations. For men, the Mifflin-St Jeor formula is BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5. For women, the constant changes to -161 instead of +5. Because of its improved accuracy, the American Dietetic Association has recommended the Mifflin-St Jeor equation as the preferred method for estimating BMR, and it is the formula used by this calculator.
Key Facts About BMR
BMR accounts for 60-75% of your total daily energy expenditure. Muscle tissue burns roughly 6 calories per pound per day at rest, while fat tissue burns about 2 calories per pound per day. BMR naturally declines by approximately 1-2% per decade after age 20, primarily due to loss of lean muscle mass. Men generally have a higher BMR than women of the same weight and height because they tend to carry more muscle mass. Sleep deprivation, extreme dieting, and prolonged stress can all suppress your metabolic rate.
Factors That Affect Your BMR
Several variables influence your basal metabolic rate beyond the age, weight, height, and gender inputs used in standard equations. Body composition is perhaps the most significant: individuals with a higher proportion of lean muscle mass burn more calories at rest than those with a higher percentage of body fat, even when total body weight is identical. Genetics also play a role, as metabolic efficiency varies between individuals. Hormonal factors, particularly thyroid hormone levels, directly regulate metabolic speed. Environmental temperature matters as well; exposure to cold can temporarily increase BMR as the body works harder to maintain core temperature. Extreme caloric restriction can cause the body to lower its metabolic rate in a survival response known as adaptive thermogenesis, which is one reason why crash diets often lead to weight regain.
BMR vs. TDEE: What Is the Difference?
While BMR measures the calories burned at complete rest, your Total Daily Energy Expenditure (TDEE) represents the full number of calories you burn in a day, including physical activity and the thermic effect of food. TDEE is calculated by multiplying your BMR by an activity factor that ranges from 1.2 for sedentary individuals to 1.9 for those with highly active lifestyles or physically demanding jobs. The thermic effect of food, which is the energy used to digest and process what you eat, adds approximately 10 percent to daily expenditure. To lose weight, you need to consume fewer calories than your TDEE, not your BMR. Eating below your BMR for extended periods is generally discouraged by nutrition professionals because it can lead to muscle loss, nutrient deficiencies, and metabolic slowdown. A moderate deficit of 300 to 500 calories below TDEE is widely considered a sustainable approach for gradual weight loss.