Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns in a 24-hour period, accounting for all activities — from basic bodily functions (BMR) to exercise, digestion, and non-exercise movement like walking, fidgeting, and daily tasks. TDEE is your true maintenance calorie level — eating at TDEE means your body weight stays stable.

TDEE is calculated by multiplying your BMR by an activity multiplier (the Katch-McArdle or Harris-Benedict activity factors). It has four main components: BMR (60–70%), the Thermic Effect of Food or TEF (8–10%), Exercise Activity Thermogenesis or EAT (15–30%), and Non-Exercise Activity Thermogenesis or NEAT (15–50%). NEAT — spontaneous activity that isn't formal exercise — is highly variable between individuals and is a major reason why two people with identical BMRs and exercise routines can have very different maintenance calorie levels.

Knowing your TDEE is fundamental for any nutrition goal. Eating 300–500 kcal below TDEE creates a sustainable fat loss deficit. Eating 250–500 kcal above TDEE supports muscle gain (lean bulk). Eating at TDEE maintains your current body composition.