The energy your body expends while you are completely at rest—your “resting calories”—is the single largest component of your daily energy use. Understanding this fundamental number is the first step in formulating an effective weight management strategy. This resting energy requirement determines the baseline for your total calorie needs, making it foundational to the concept of a calorie deficit necessary for weight loss.
Defining Resting Calories (Basal Metabolic Rate)
The scientific term for resting calories is Basal Metabolic Rate (BMR) or Resting Energy Expenditure (REE). This measurement represents the minimum energy the body needs to maintain basic life functions, such as breathing, blood circulation, and organ function, in a state of complete rest. These are the calories required just to keep the body running.
BMR is traditionally measured under very strict laboratory conditions, requiring a person to be fully rested and fasted for 12 hours. Resting Energy Expenditure (REE) is a more practical measurement taken under less strict conditions, usually after a short period of rest. While BMR is technically slightly lower than REE, the two terms are often used interchangeably because they differ by only about 10 percent.
How Resting Calories Form the Foundation of Total Expenditure
Resting calories are the primary driver, forming the bulk of your Total Daily Energy Expenditure (TDEE). The energy expended at rest accounts for 60% to 75% of the TDEE for the average person. This makes BMR/REE the most significant figure in determining your overall calorie needs.
The TDEE is the sum of three main components: Basal Metabolic Rate (BMR), the Thermic Effect of Food (TEF), and Activity Energy Expenditure (AEE). The TEF is the energy used to digest, absorb, and process food, accounting for about 10% of TDEE. The AEE covers all physical movement, including structured exercise and Non-Exercise Activity Thermogenesis (NEAT).
Since resting calories represent the largest portion of TDEE, this number is foundational to achieving weight loss. Weight loss occurs when you consistently consume fewer calories than your TDEE, creating a calorie deficit. Knowing your resting calorie burn is the starting point for calculating your total daily expenditure and setting an effective target for that deficit.
Factors That Influence Your Resting Calorie Burn
Resting calorie burn is not a fixed number and is significantly influenced by several biological and lifestyle factors. Body composition is the most impactful variable, as muscle tissue is far more metabolically active than fat tissue. Individuals with a higher percentage of lean muscle mass will have a higher BMR/REE because muscle burns more calories at rest compared to fat.
Age is another major factor, with BMR naturally decreasing as people get older, declining by 1–2% per decade after age 20. This decline is primarily linked to the age-related loss of muscle mass, though hormonal and neurological changes also play a role. Sex also creates a difference, as men generally possess a higher BMR than women due to having a greater average body size and higher proportion of lean muscle mass.
Genetic makeup can influence an individual’s basal rate. The function of the thyroid gland, which produces hormones that regulate metabolism, is a medical factor with a substantial impact on BMR. Optimizing body composition by building lean muscle remains one of the few actionable ways to influence your resting calorie burn.