The Mathematics of Weight Loss: TDEE and Deficits
Fad diets come and go, but the fundamental law of thermodynamics remains constant: to lose weight, you must consume fewer calories than your body expends. To gain weight, you must consume more. This is the foundation of the Calorie Deficit Calculator.
Understanding BMR vs. TDEE
Your Basal Metabolic Rate (BMR) is the number of calories your body burns just to stay alive while completely at rest (breathing, pumping blood).
Your Total Daily Energy Expenditure (TDEE) is your BMR multiplied by your physical activity level. Your TDEE is your "Maintenance Calories"—the exact amount of food you need to stay at your current weight.
Setting a Safe Calorie Deficit
One pound of body fat contains roughly 3,500 calories. Therefore, to lose 1 pound (0.45 kg) per week, you need a daily calorie deficit of 500 calories (500 x 7 days = 3,500).
Warning: Never set your calorie target below your BMR. Extreme starvation diets cause muscle loss and metabolic damage. A deficit of 300 to 500 calories below your TDEE is the sweet spot for sustainable fat loss.