A TDEE (Total Daily Energy Expenditure) calculator estimates the number of calories you burn daily, accounting for your basal metabolic rate (BMR) and activity level. It’s used to guide nutrition and fitness goals, such as weight loss, maintenance, or muscle gain. You input details like age, weight, height, gender, and activity level, and the calculator provides a calorie estimate. For weight loss, consume fewer calories than your TDEE; for gain, consume more. It’s a helpful starting point but may need adjustments based on individual factors like metabolism or lifestyle changes and muscle mass.