How does the calculation work?

Basal Metabolic Rate (BMR) is the energy your body consumes at rest, estimated using the Mifflin-St Jeor formula based on sex, age, height, and weight. Multiplying it by your activity level gives your Total Daily Energy Expenditure (TDEE).

To lose weight, you need a moderate calorie deficit; to gain mass, a slight surplus: the calorie target applies this correction to your daily needs.