BMR vs daily calories
BMR (Basal Metabolic Rate) is what your body burns just to keep you alive - breathing, circulation, temperature. Multiplying it by an activity factor gives your total daily energy expenditure, the calories that keep your weight stable.
Losing weight safely
A deficit of about 500 kcal a day leads to roughly 0.5 kg of weight loss per week. Very low-calorie diets (below about 1,200 kcal for women or 1,500 kcal for men) should only be followed under medical supervision.
When weight won't change
If you are eating less and still not losing weight, or gaining weight without eating more, an under-active thyroid, insulin resistance, PCOS or certain medicines can be the reason. A thyroid profile and HbA1c are good first checks.