TDEE — Total Daily Energy Expenditure — is the total calories you burn in a day. Eat below it, you lose weight. Eat above it, you gain. It's the single most useful number in nutrition.
BMR (Basal Metabolic Rate): what you'd burn lying in bed all day. Roughly 60–70% of TDEE.
Activity: exercise plus daily movement (NEAT). 15–30% of TDEE for most people.
TEF (Thermic Effect of Food): calories burned digesting. About 10%.
For weight loss: subtract 500 kcal/day from TDEE for ~1 lb/week loss.
For maintenance: eat at TDEE, adjust by ±100 kcal after 2 weeks based on the scale.
For muscle gain: add 200–300 kcal above TDEE with resistance training.
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