The terminology used by fitness trackers and health apps often confuses how our bodies burn calories daily. These devices frequently report two separate numbers: “Resting Energy” and “Active Energy,” leading people to wonder if they should be added together. The simple answer is yes, these two categories are intended to be combined because they represent the major components of your total daily energy expenditure. Understanding these terms is the first step in accurately managing your energy balance for weight maintenance or change.
Defining Resting Energy Expenditure
Resting Energy Expenditure (REE) represents the energy your body uses to maintain life-sustaining functions while you are completely at rest. This includes fundamental processes like breathing, circulating blood, regulating body temperature, and basic organ function. REE is often used interchangeably with Basal Metabolic Rate (BMR), though BMR is technically measured under stricter, more controlled laboratory conditions. This baseline burn accounts for the largest share of your daily calorie expenditure, typically 60 to 75% of your Total Daily Energy Expenditure (TDEE). The rate of your REE is determined primarily by fixed personal characteristics, such as age, sex, weight, and especially lean muscle mass.
Defining Active Energy Expenditure
Active Energy Expenditure (AEE) is the energy the body burns that is above the resting metabolic rate. This category encompasses all the movement and physical activity performed throughout the day. AEE is the most variable component of your daily energy burn, changing significantly based on your lifestyle. This expenditure breaks down into two main types of activity. The first is planned exercise, or Exercise Activity Thermogenesis (EAT), which includes structured activities like running or lifting weights. The second, Non-Exercise Activity Thermogenesis (NEAT), involves all other incidental movement, such as walking, fidgeting, standing, or doing chores. The “Active Calories” displayed on fitness devices typically represent this entire AEE component.
Calculating Total Daily Energy
The most direct answer to whether to add resting and active energy is that they are mathematically required to calculate your Total Daily Energy Expenditure (TDEE). TDEE is the total number of calories your body burns in a 24-hour period. The simplified formula used by many health professionals and fitness trackers is TDEE = REE + AEE. Fitness trackers use your estimated REE, calculated from your personal data, as the foundation for the daily total. They then continuously monitor heart rate and movement to measure AEE, the energy burned in addition to your resting rate. The final daily calorie count displayed by these devices is the sum of these two components, which is essential for managing weight.
The Third Pillar: Thermic Effect of Food
While REE and AEE form the bulk of the calculation, there is a third, smaller component of TDEE known as the Thermic Effect of Food (TEF). TEF is the energy the body expends to digest, absorb, transport, and store nutrients from the food you eat. This mandatory metabolic process occurs every time you consume calories. TEF is a small but consistent contributor, usually accounting for 5 to 10% of your Total Daily Energy Expenditure. The exact energy cost varies depending on the macronutrient composition of the meal; protein requires significantly more energy to process than carbohydrates or fats. Since TEF is relatively small and difficult for consumer devices to estimate accurately, it is often omitted from the simplified REE + AEE formula presented to the public.