BMR Calculator

BMR (men) = 10×kg + 6.25×cm − 5×age + 5

Health & Body

How to Use This Tool

BMR calculator

Enter your age, sex, height, and weight to estimate your Basal Metabolic Rate. BMR is the number of calories your body burns at complete rest just to keep you alive: breathing, circulating blood, maintaining body temperature, and repairing cells. This page covers the formulas behind the calculation, how activity levels change your daily calorie needs, and common questions about metabolism.

What BMR tells you

BMR accounts for about 60 to 75 percent of the calories most people burn in a day. The rest comes from physical activity and the thermic effect of food (the energy your body uses to digest meals). Knowing your BMR gives you a baseline. Multiply it by an activity factor and you get an estimate of Total Daily Energy Expenditure (TDEE), the number you actually need for meal planning or weight management.

BMR is not the same as Resting Metabolic Rate (RMR), though the two are close. BMR is measured under strict lab conditions after 8 hours of sleep and 12 hours of fasting. RMR is measured under less strict conditions and tends to run about 10 percent higher. Most online calculators, including this one, use BMR formulas but the practical difference is small.

BMR formulas

Mifflin-St Jeor equation

This is the formula most dietitians recommend today. It was published in 1990 and has been found to predict measured BMR within 10 percent for most people.

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

Example: A 30-year-old man who weighs 80 kg and is 178 cm tall has a BMR of (10 x 80) + (6.25 x 178) – (5 x 30) + 5 = 800 + 1,112.5 – 150 + 5 = 1,767.5 calories per day.

Harris-Benedict equation (revised)

The original Harris-Benedict equation dates to 1919 and was revised by Roza and Shizgal in 1984. It tends to estimate slightly higher than Mifflin-St Jeor.

For men: BMR = (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years) + 88.362

For women: BMR = (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years) + 447.593

Katch-McArdle formula

This formula uses lean body mass instead of total weight, which makes it more accurate for people who know their body fat percentage.

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

Lean body mass = weight x (1 – body fat percentage as a decimal). A person who weighs 80 kg at 20 percent body fat has a lean mass of 80 x 0.80 = 64 kg, giving a BMR of 370 + (21.6 x 64) = 1,752 calories.

Activity multipliers for TDEE

Multiply your BMR by the factor that best matches your typical week to estimate total daily calories burned.

Activity level Description Multiplier
Sedentary Desk job, little or no exercise 1.2
Lightly active Light exercise 1 to 3 days per week 1.375
Moderately active Moderate exercise 3 to 5 days per week 1.55
Very active Hard exercise 6 to 7 days per week 1.725
Extra active Very hard exercise plus a physical job 1.9

Using the earlier example: a 30-year-old man with a BMR of 1,768 who exercises moderately would have a TDEE of about 1,768 x 1.55 = 2,740 calories per day.

Factors that affect BMR

Age lowers BMR. After about age 20, BMR drops roughly 1 to 2 percent per decade, mainly because muscle mass decreases over time. Strength training can slow this decline.

Body composition matters more than weight alone. Muscle tissue burns more calories at rest than fat tissue. Two people who weigh the same but carry different amounts of muscle will have different BMRs.

Sex affects BMR because men tend to have more muscle mass and less body fat than women of the same height and weight. The Mifflin-St Jeor equation accounts for this with the +5 (men) and -161 (women) constants.

Genetics, hormones (particularly thyroid hormones), and ambient temperature also play a role. Fever increases BMR by about 7 percent for each degree Fahrenheit above normal. Extreme calorie restriction can lower BMR by 20 percent or more as the body adapts to conserve energy.

Tips for using BMR estimates

  • Treat the number as an estimate, not a precise measurement. The Mifflin-St Jeor formula predicts within 10 percent of measured BMR for most people, which means a calculated BMR of 1,700 could actually be anywhere from 1,530 to 1,870.
  • Use metric measurements for the most accurate results. If you start with pounds and inches, convert before plugging into the formula: multiply pounds by 0.4536 for kilograms, multiply inches by 2.54 for centimeters.
  • Recalculate every few months if your weight or activity level changes significantly. A 10 kg weight change can shift BMR by 100 calories or more.
  • Do not eat below your BMR for extended periods without medical supervision. Your body needs that baseline just to maintain organ function.

BMR compared to RMR

BMR requires overnight fasting, complete rest, and a temperature-controlled room. RMR is measured after a shorter fast (3 to 4 hours) without the strict environmental controls. RMR is easier to measure in a clinical setting, which is why most lab tests actually measure RMR and label it as such.

For practical purposes, the difference is small enough that most people can use the terms interchangeably when planning meals or tracking calories. The formulas on this page calculate BMR, but the result is close enough to RMR for everyday use.

Frequently asked questions

What is a normal BMR?

For adult men, BMR typically falls between 1,600 and 1,800 calories per day. For adult women, it usually falls between 1,300 and 1,500. Active people with more muscle mass will be at the higher end of these ranges.

How do I increase my BMR?

Building muscle through resistance training is the most effective way. Each pound of muscle burns roughly 6 calories per day at rest, compared to about 2 calories per pound of fat. Staying hydrated and getting enough sleep also support a healthy metabolic rate.

Does eating less lower my BMR?

Yes. Extended calorie restriction causes adaptive thermogenesis, where the body reduces energy expenditure to conserve fuel. This is one reason very low calorie diets often produce diminishing returns over time. Gradual calorie reduction (250 to 500 calories below TDEE) minimizes this effect.

Which BMR formula is most accurate?

The Mifflin-St Jeor equation is recommended by the Academy of Nutrition and Dietetics as the most reliable for healthy adults. The Katch-McArdle formula may be more accurate if you know your body fat percentage, especially if you carry significantly more or less muscle than average.

Can I measure my actual BMR?

Yes, through indirect calorimetry. You breathe into a device that measures oxygen consumption and carbon dioxide production for 15 to 20 minutes. The test is available at some hospitals, sports medicine clinics, and fitness centers, typically costing $75 to $250.

How is BMR different from TDEE?

BMR is the calories your body burns doing nothing. TDEE adds physical activity and the thermic effect of food. TDEE is always higher than BMR. For weight maintenance, you eat at your TDEE. For weight loss, you eat below it.

Measurement guides

Formula & Explanation

The Mifflin-St Jeor equation was published in 1990 and is currently the formula recommended by the American Dietetic Association for estimating BMR in healthy adults.