Several equations to predict the number of calories required by humans have been published from the early 20th–21st centuries. In each of the formulas below:
: P is total heat production at complete rest,
: m is mass (kg),
: h is height (cm),
: a is age (years).
;The original Harris–Benedict equation
Historically, the most notable formula was the Harris–Benedict equation, which was published in 1919:
: for men, 
: for women, 
The difference in BMR for men and women is mainly due to differences in body mass. For example, a 55-year-old woman weighing  and  tall would have a BMR of  per day.
;The revised Harris–Benedict equation
In 1984, the original Harris–Benedict equations were revised using new data. In comparisons with actual expenditure, the revised equations were found to be more accurate:
: for men, 
: for women, 
It was the best prediction equation until 1990, when Mifflin et al. introduced the equation:
;The Mifflin St Jeor equation
where s is +5 for males and −161 for females.
According to this formula, the woman in the example above has a BMR of  per day.
During the last 100 years, lifestyles have changed, and Frankenfield et al. showed it to be about 5% more accurate.
These formulas are based on body mass, which does not take into account the difference in metabolic activity between lean body mass and body fat. Other formulas exist which take into account lean body mass, two of which are the Katch–McArdle formula and Cunningham formula.
;The Katch–McArdle formula (resting daily energy expenditure)
The Katch–McArdle formula is used to predict resting daily energy expenditure (RDEE).
The Cunningham formula is commonly cited to predict RMR instead of BMR; however, the formulas provided by Katch–McArdle and Cunningham are the same.
where ℓ is the lean body mass (LBM in kg):
where f is the body fat percentage.
According to this formula, if the woman in the example has a body fat percentage of 30%, her resting daily energy expenditure (the authors use the term of basal and resting metabolism interchangeably) would be 1262 kcal per day.