BMR Calculator

BMR (Basal Metabolic Rate)

The body requires energy to function, to do "work". Everything the body does, such as walking, exercising and thinking uses up or "expends" energy. The energy required for the body to function is obtained through nutrition; food and drinks. Food and drinks contain and deliver energy, measured in calories, that can be used to do work. It is intuitive that activities such as exercising require energy. BMR however, is the energy expenditure of the body at rest. That is the work the body does to perform its basic functions such as breathing, keeping itself at an optimal temperature, and even growing hair or nails. BMR can thus only be reliably calculated if there are no, or realistically, as little as possible, external factors that require the body to expend excess energy.

BMR reflects calories burned per day if:

• The body has been fasting for about ten to twelve hours.
• No physical and/or mental activities are performed.
• The environment temperature the body is in is around 22°C/72°F.

This way the body does not expend extra energy to digest, do physical/mental activities or keep itself warm at extreme environmental temperatures.

BMR accounts for roughly 66-70% of the total daily energy expenditure (TDEE) and is thus a good source of information for estimating the daily required caloric intake. Knowing your required caloric intake helps achieving certain fitness and health goals, such as battling obesity.

Estimating BMR

Because the body is a complex system, much research has been conducted to find the factors that most accurately calculate BMR. No equation can calculate BMR with 100% accuracy; accuracies of 50-70% are more realistic. This calculator uses the Mifflin-St Jeor formula based on the work of Mifflin et al. (1990). The base formula is drafted using a stratified random sample of almost 500 participants, including men and women, people of different ages and normal-weight and obese people. The Miffling-St Jeor equation is as follows:

• W = weight in kilograms.
• H = height in centimeters.
• A = age in years.
• β₀ is the intercept

The intercept in this equation makes little practical sense as, for example, a weight of 0 is impossible. β₁, β₂ and β₃ are the weights and denote the relative importance of the factors in estimating BMR. Mifflin et al. suggest that better accuracy is obtained if the intercept is separated by gender. Thus the equation with values is as follows:

For men:

For women:

Do note that every body is unique. The most accurate BMR estimate is calculated by a specialist that uses validated devices for the calculation. Any formula presented online is generic and not tailored to your unique body. See the next section to see how BMR may differ for different demographics.

BMR Special Cases

Pregnant women

Growing a baby requires more energy than usual, and the BMR of pregnant women will thus be higher than the calculator indicates.

Breastfeeding and menopausing women

Hormonal changes during breastfeeding and menopause make it harder to distinguish the normal energy at rest used from the energy used for breastfeeding/menopausing. BMR during breastfeeding is somewhat higher and somewhat lower for women during menopause.

Children and teens

Children and teens are subject to many bodily changes and phases of growth before reaching adulthood. Thus, the effect of age in children is much more pronounced than those in adults. This means that the calculated BMR of children and teens is usually somewhat different than the calculator will indicate.

Non-Caucasian population

Most research, especially older research, is done on Caucasian participants. It is likely that the Mifflin-St Jeor equation, drafted in 1990, also had a majority of Caucasian participants. The values in the equation may be somewhat different for other races, as suggested by other research (Sabounchi et al., 2013; Frankenfield et al., 2005).

Athletes and muscular individuals

One of the best contributors to BMR is the fat free mass of individuals. This is much higher in athletes in muscular individuals and thus the BMR for this group is higher than the calculation will indicate.

References

• Frankenfield, D., Roth-Yousey, L., Compher, C., & Evidence Analysis Working Group. (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic association, 105(5), 775-789.


• Mifflin, M. D., St Jeor, S. T., Hill, L. A., Scott, B. J., Daugherty, S. A., & Koh, Y. O. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American journal of clinical nutrition, 51(2), 241-247. Sabounchi, N. S., Rahmandad, H., & Ammerman, A. (2013).


• Sabounchi, N. S., Rahmandad, H., & Ammerman, A. (2013). Best-fitting prediction equations for basal metabolic rate: informing obesity interventions in diverse populations. International journal of obesity, 37(10), 1364-1370.