You burn calories even when resting through basic life-sustaining functions like breathing, circulation, nutrient processing, and cell production. This is known as basal metabolic rate (BMR).

Read on to learn more about how to calculate BMR and what it may mean.

Basal metabolic rate (BMR) is often used interchangeably with resting metabolic rate (RMR).

While BMR is the minimum number of calories required for basic functions at rest, RMR — also called resting energy expenditure (REE) — is the number of calories that your body actually burns while it’s at rest.

Although BMR and RMR slightly differ, your RMR should be an accurate estimate of your BMR. The two values tend to vary by about 10%.

One popular way to estimate BMR is through the Harris-Benedict formula, which takes into account weight, height, age, and sex.

Females assigned at birth (FAABs)

BMR = 655 + (9.6 x weight in kg) + (1.8 x height in cm) – (4.7 x age in years)

Males assigned at birth (MAABs)

66 + (13.7 x weight in kg) + (5 x height in cm) – (6.8 x age in years)

Your BMR can be used to help you gain, lose, or maintain your weight. By knowing how many calories you burn, you can know how many to consume. To put it simply:

That said, there are many factors that can influence your weight. They include:

  • your level of physical activity
  • your sex
  • your age
  • any health conditions you have or medications you take
  • your metabolism
  • your gut microbiome

Counting calories by itself is not always enough to lose weight. Many doctors today argue that what you eat matters much more.

For this reason, your BMR might not give you the full context you need to understand what lifestyle changes you can make to achieve weight loss.

If you want to get an idea of how many calories you should eat daily and you’ve estimated your BMR using the Harris-Benedict formula, your next step is to include the number of calories you burn during daily activities based on your lifestyle:

  • Sedentary: If you get minimal or no exercise, multiply your BMR by 1.2.
  • Lightly active: If you exercise lightly one to three days a week, multiply your BMR by 1.375.
  • Moderately active: If you exercise moderately three to five days a week, multiply your BMR by 1.55.
  • Very active: If you engage in hard exercise six to seven days a week, multiply your BMR by 1.725.
  • Extra active: If you engage in very hard exercise six to seven days a week or have a physical job, multiply your BMR by 1.9.

The final number is approximately how many calories you need on a daily basis to maintain your weight.

Of course, this is an estimate. According to a 2021 study, the formula would be more accurate if it included body composition, weight history, and other factors that have been shown to affect BMR.

However, to get the most accurate idea is to have a trained technician perform indirect calorimetry, which is a study of your metabolism. This test measures how much oxygen (O2) you take in and how much carbon dioxide (CO2) you take out when you breathe. The quantity of these gases varies depending on how your body metabolizes different macronutrients such as carbs, fats, and protein for energy.

Your BMR is determined by a number of factors, including:

Of these factors, you can take steps to change your weight and body composition. So if you want to change your BMR, your first step should be to increase muscle.

For example, a 2018 study suggests that resistance training is an effective means of boosting BMR levels among a group of inactive adult women. However, this won’t necessarily translate to weight loss, according to the researchers.

Understanding your BMR, your typical activity level, and the amount of calories you need daily to maintain your weight are important ways for you to actively participate in your physical health.

Whether you need to gain weight, maintain your current weight, or lose weight, calculating your BMR is a good place to start.