Total Daily Energy Expenditure (TDEE) quantifies the number of calories you burn in a day. This measure is best estimated by scaling your Basal Metabolic Rate to your level of activity. TDEE is critical in tailoring your nutrition plan to desired fitness goals.
Here is the calculator:
1: Fill out your stats
2: Eat less kcal than it says = lose weight
(eating more = gaining weight)
It's really that simple.