TDEE is the foundational number underneath any calorie target. Maintenance, fat-loss, and muscle-gain calorie targets are all built by adjusting TDEE up or down by a chosen offset.
TDEE has four components:
- Basal metabolic rate (BMR) — the calories your body burns at complete rest to keep organs, brain, and basic processes running. Usually 60-70% of TDEE.
- Thermic effect of food (TEF) — the calories spent digesting and metabolizing what you eat. Usually 8-10% of TDEE for typical mixed diets, higher on protein-heavy days.
- Exercise activity thermogenesis (EAT) — calories from planned workouts. Highly variable; from 5% of TDEE for sedentary people to 30%+ for endurance athletes.
- Non-exercise activity thermogenesis (NEAT) — calories from incidental movement, posture, fidgeting, walking, household activity. Often the most variable component between two people of similar size.
The standard estimation method is the Mifflin-St Jeor equation, which calculates BMR from weight, height, age, and sex, then multiplies by an activity factor (1.2 for sedentary up to 1.9 for very active) to get TDEE.
The honest caveat: published validation of these formulas finds typical errors of 10-15% from true measured expenditure. A TDEE estimate is a starting hypothesis, not the answer. The right workflow is to eat at calculated maintenance for two weeks and adjust based on whether weight is stable, drifting up, or drifting down.
NEAT is the component that adapts most during a sustained calorie deficit. As intake drops, the body reduces incidental movement to conserve energy, which is one reason a calculated 500 kcal deficit often produces less weight loss than the math suggests after week six to eight.