Total Daily Energy Expenditure (TDEE)
The total number of calories a person burns in a day, including basal metabolism, the thermic effect of food, and physical activity.
Total Daily Energy Expenditure (TDEE) is the sum of all calories burned in a 24-hour period. It is conventionally decomposed into:
- Basal Metabolic Rate (BMR) — calories burned to keep the body alive at rest. Roughly 60-70% of TDEE in a sedentary adult.
- Thermic Effect of Food (TEF) — calories burned digesting food. Roughly 10% of TDEE; higher for protein.
- Non-Exercise Activity Thermogenesis (NEAT) — fidgeting, posture, daily movement. Highly variable.
- Exercise Activity Thermogenesis (EAT) — intentional exercise.
How calorie tracking apps estimate TDEE
Most apps estimate BMR using predictive equations (Mifflin-St Jeor, Harris-Benedict, Katch-McArdle), then multiply by an activity factor for NEAT+EAT. These estimates carry roughly ±10-15% error vs measured TDEE (doubly labeled water) in adults — meaningfully larger than the per-meal MAPE we measure for app calorie lookups.
For weight management, the practical implication is that the deficit/surplus you see in an app is an estimate, not a measurement. We weight UX scoring partly on whether an app frames its TDEE estimate appropriately (with confidence bands, not as a precise number).
The clinical gold standard for measuring TDEE is doubly labeled water (DLW). Indirect calorimetry can measure resting metabolic rate but not free-living TDEE.