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 a post-absorptive state (when the digestive system is quiescent, which needs approximately 12 hours of fasting).
The basal metabolic rate (BMR) is the 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 expenditure, whereas food digestion, or thermogenesis, accounts for about 10%.
The BMR is assessed while awake under extremely tight conditions. A person's sympathetic nervous system must be entirely rested to obtain an accurate BMR measurement. Basal metabolism is typically the greatest portion of a person's 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.
The BMR is usually 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 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. The Mifflin-St Jeor Equation is often regarded as the most accurate equation for determining BMR, except the Katch-McArdle Formula, which may be more accurate for slimmer persons who know their body fat %. You can select the equation for the computation by opening the options.
Mifflin-St. Jeor For men: BMR = 10W + 6.25H - 5A + 5.
For women, BMR equals 10W + 6.25H - 5A - 161.
Revised Harris-Benedict 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:
Body weight (kg) and height (cm)
A represents age, and F indicates body fat percentage.
BMR Variables
Muscle Mass: Aerobic exercises like running and cycling have little effect on BMR. Anaerobic workouts, 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 necessary 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 features passed 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 elevate BMR when 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: Consuming small, well-spaced meals increases BMR. Conversely, famine can lower BMR by up to 30%, like a phone that goes into power-saving mode with 5% of its battery left, a human body will compromise energy levels, moods, bodily physique maintenance, and mental functions to use the limited caloric energy available to support it more efficiently.
Pregnancy: Ensuring the survival of a distinct fetus boosts BMR. This explains why pregnant women consume more than usual. Menopause can also increase or decrease BMR based on hormonal changes.
Supplements: Some supplements or medications increase BMR, mostly to aid weight loss. Caffeine is a common one.
Online BMR testing relies on rigid algorithms and may not accurately determine an individual's BMR. Visiting a licensed specialist or assessing BMR using a calorimetry instrument is preferable. These mobile devices are widely available at health and fitness clubs, medical offices, and weight-loss clinics
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
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. 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 only partially correct. Because not all human body functions are fully understood, 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. However, keeping a daily journal of exercise, food consumption, and so on can help track the factors contributing to any given result and determine what works and needs improvement. Tracking progress in a notebook and making adjustments as needed over time is typically the best indicator of success toward personal goals.
Reference: Johnstone AM, Murison SD, Duncan JS, Rance KA, Speakman JR. Factors influencing variation in basal metabolic rate include fat-free mass, fat mass, age, and circulating thyroxine, but not sex, leptin, or triiodothyronine1. American Journal of Clinical Nutrition 2005;82:941-948.