Teenage girls need more, too: 1,800 to 2,200 calories a day if they're ages 11 to 13, and 1,800 to 2,400 calories a day if they're age 14 to 18. Gender, body size, growth rate and activity level specifically determine how many calories teens need. Those involved in strenuous physical activity such as soccer, basketball, football or other sports may need 3,500 calories (more or less) daily. American Dietetic Association Complete Food and Nutrition Guide, 3rd ed.