Basal Metabolic Rate, or BMR, is the number of calories your body burns while at rest, to maintain normal body functions, such as temperature, heart beat, digestion, and breathing. This is the minimum of calories your body needs if you lie all day in a bed. Please see the Calorie Planning Guideline for more details.
We use Mifflin formula for estimating Basal Metabolic Rate. We do not support customization of BMR as this not included in daily and weekly energy balance calculation. However, we use the BMR value as a safeguard to detect if the calculated calorie target becomes critically low — specifically, when it drops below 80% of your BMR. In such cases, the system interprets this as a sign that your weight loss goal may be too aggressive (e.g., trying to lose too much weight in too short a period).
A Calorie Budget that falls below your BMR can be harmful to your health and should only be followed with the guidance of a registered dietitian or under medical supervision. Additionally, dietitians typically recommend limiting weight loss to no more than 2 pounds per week, and weight gain to no more than 1 pound per week.
See also how Weight Maintenance Calories are calculated. Additionally, you can review how to modify the method used to calculate energy needs, including options such as RMR, BMR using the Mifflin-St. Jeor or Katch-McArdle equations, as well as entering your own custom value.