Basal Metabolic Rate (BMR) is the number of calories your body needs to maintain basic physiological functions at complete rest — breathing, circulation, cell production, and temperature regulation. BMR accounts for 60–75% of total energy expenditure in sedentary individuals.
TDEE (Total Daily Energy Expenditure) multiplies BMR by an activity factor to estimate total daily calorie needs. To lose weight, aim for 500 kcal below your TDEE (roughly 0.5 kg/week loss). To gain weight, add 500 kcal above maintenance.
The Mifflin-St Jeor equation (1990) is considered the most accurate for general use. The Harris-Benedict equation (revised 1984) is an older but widely recognised alternative.