It depends on the age of the teen. Young teens are still growing and developing, so calorie counting and deprivation is not a good idea. The best thing to do is determine, based on body weight, how many calories are needed each day to maintain that weight. Then, if possible, lower that amount to create a calorie deficit each day. By adding exercise and other activities, more calories are burned. A pound is 3500 calories, so if the daily intake is decreased by 500 calories a day, that's a loss of one pound per week. Refer to the government guidelines regarding nutrition: www.nutrition.gov