Your total daily energy expenditure explained.
TDEE = BMR × Activity Factor. BMR (Mifflin-St Jeor) accounts for ~60–70% of TDEE. Activity adds 20–40%. Thermic effect of food adds ~10%. To lose weight: eat below TDEE (deficit of 500 kcal/day ≈ 0.5 kg/week). To gain: eat above. Track for 2–3 weeks and adjust based on actual weight changes.