Basal Metabolic Rate (BMR)

BMR stands for basal metabolic rate and represents the number of calories you would burn in a day if you were inactive and stayed in bed all day. The BMR calculator allows you to calculate not only the number of calories you burn when inactive, but also a daily calorie figure that takes into account your lifestyle activity level. These two figures together give you a representative figure for your daily calorie intake.
It is important to bear in mind that BMR calculations do not take into account for lean body mass, which will obviously have a factor of its own. Very muscular people, for example, will receive a figure that probably under-estimates their calorie needs and very overweight people will likely get a calculation that over-estimates their calorie requirements.
Let's take a look at the formula for BMR...

The Mifflin - St Jeor BMR Formula

In 1990, a study by Mifflin MD and St Jeor was published in the American Journal of Clinical Nutrition. It discussed a new predictive equation for resting energy expenditure in healthy individuals, suggesting an update to the existing Harris-Benedict method. The Mifflin - St Jeor equation was said to be more predictive for modern lifestyles and has established itself as the standard for calculating BMR estimates.
The formulae used by this calculator with the Mifflin - St Jeor equation are as follows:

The Harris-Benedict BMR Formula

The original Harris-Benedict equation was created in 1919 following a study by James Arthur Harris and Francis Gano Benedict. The equations were revised in 1984 using new data, in order to improve accuracy. The Harris-Benedict equation was commonly used for BMR calculations until 1990, when the Mifflin St Jeor equation was published.
The formulae used by this calculator with the Harris-Benedict equation are as follows: