The Basal Metabolic Rate (BMR) Calculator calculates your basal metabolic rate—the amount of energy expended while at rest in a neutrally temperate atmosphere and in a post-absorptive state (when the digestive system is quiescent, which needs approximately 12 hours of fasting).

The basal metabolic rate (BMR) is the amount of energy required while resting in a temperate climate and the digestive system is quiescent. It’s equivalent to calculating how much petrol an idle car uses while parked. In this state, energy will only be required to support important organs such as the heart, brain, kidneys, nervous system, intestines, liver, lungs, sex organs, muscles, and skin. Upkeep consumes approximately 70% of a person’s daily energy (calories). Physical activity accounts for approximately 20% of total expenditure, whereas food digestion, commonly known as thermogenesis, accounts for about 10%.

The BMR is tested while awake under extremely tight conditions. To obtain an accurate BMR measurement, a person’s sympathetic nervous system must be entirely rested. Basal metabolism is typically the greatest portion of a person’s total caloric requirements. The daily calorie demand is calculated by multiplying the BMR by a factor ranging from 1.2 to 1.9, depending on activity level

In most cases, the BMR is approximated using formulae derived from statistical data. The Harris-Benedict Equation was one of the first equations introduced. It was updated in 1984 to be more precise and was used until 1990, when the Mifflin-St Jeor Equation was implemented.The Mifflin-St Jeor Equation was shown to be more accurate than the improved Harris-Benedict Equation. The Katch-McArdle Formula differs in that it calculates resting daily energy expenditure (RDEE) while accounting for lean body mass, which neither the Mifflin-St Jeor nor the Harris-Benedict Equation do. It was updated in 1984 to improve accuracy and was used until 1990, when the Mifflin-St Jeor Equation was developed. Of these formulae, the Mifflin-St Jeor Equation is regarded as the most accurate for determining BMR, with the exception that the Katch-McArdle Formula may be more accurate for persons who are slimmer and know their body fat %. You can select the equation to use in the computation by opening the options.

The three equations used by the calculator are listed below:

Mifflin-St Jeor Equation:

For men:

BMR = 10W + 6.25H – 5A + 5

For women:

BMR = 10W + 6.25H – 5A – 161

Revised Harris-Benedict Equation:

For men:

BMR = 13.397W + 4.799H – 5.677A + 88.362

For women:

BMR = 9.247W + 3.098H – 4.330A + 447.593

Katch-McArdle Formula:

BMR = 370 + 21.6(1 – F)W

where:

W is body weight in kg

H is body height in cm

A is age

F is body fat in percentage

BMR Variables

Muscle Mass – Aerobic exercises like running and cycling have little effect on BMR.  Anaerobic exercises, such as weightlifting, indirectly increase BMR by building muscle mass, which increases resting energy consumption. The more muscle mass an individual has in their physical composition, the greater the BMR required to keep their body at a specific level.

Age – The more senior and limber an individual is, the lower their BMR, or the minimum calorie intake required to keep their organs operating at a given level.

Genetics – Hereditary qualities given down from ancestors influence BMR.

Weather – Cold surroundings increase BMR due to the energy required to maintain a homeostatic body temperature.  Similarly, excessive external heat can raise BMR as the body expends energy to cool its internal organs.  BMR increases by about 7% for every 1.36 degrees Fahrenheit increase in the body’s internal temperature.

Diet – Small, consistently distributed meals boost BMR. On the other side, famine can lower BMR by up to 30%. A human body, like a phone that goes into power-saving mode when it has 5% of its battery left, will make compromises such as energy levels, moods, bodily physique maintenance, and mental functions in order to more efficiently use the limited caloric energy available to support it.

Pregnancy – Ensuring the survival of a distinct fetus improves BMR. This explains why pregnant women consume more than usual. Menopause can also affect BMR, increasing or decreasing it based on hormonal changes.

Supplements – Certain vitamins or medicines enhance BMR, mostly to aid with weight loss. Caffeine is a common one.

BMR Tests

Online BMR testing using inflexible formulas are not the most accurate way to calculate an individual’s BMR. It is preferable to visit a licensed specialist or assess BMR using a calorimetry instrument. These mobile devices are widely available at health and fitness clubs, medical offices, and weight-loss clinics.

Resting Metabolic Rate

While the terms are used interchangeably, there is a significant distinction between their definitions. Resting metabolic rate, or RMR for short, is the rate at which the body spends energy while relaxed but not completely inactive. It is also known as resting energy expenditure, or REE. BMR measures must be in total physiological balance, whereas RMR measurements can be influenced and defined by contextual constraints.

Modern Wisdom

A 2005 meta-analysis of BMR* found that even after controlling for all factors influencing metabolic rate, there is still a 26% unknown variance between individuals. Essentially, an average person eating an average diet will have predicted BMR values, however there are still unknown elements that influence BMR specifically.

As a result, even the most precise BMR estimations performed by specialists will not be completely correct.  Because not all human body functions are fully understood at this time, determining total daily energy expenditure (TDEE) based on BMR estimates is only an approximation.  BMR can help build the groundwork for any health or fitness goal, but it has little further to give beyond that. A calculated BMR and thus TDEE may produce unsatisfactory results due to rough estimates, but keeping a daily journal of exercise, food consumption, and so on can help track the factors that contribute to any given result and determine what works and what needs to be improved. Tracking progress in a notebook and making revisions as needed over time is typically the best indicator of success toward personal goals.