Help, how much calcium can a teenage girl have per day?

1200mg daily. Anywhere from 1000-1300mg daily is sufficient during teeage years to ensure good bone mineralization and prevention of osteoporosis later in life. Just to give you an example, an 8 oz of low fat yogurt and 1 cup of milk both have approximately 300mg of calcium. Make sure there is also adequate vitamin d intake as calcium absorption from the gut is predominantley vitamin d dependent.
800-1000 mg. 800 to 1000 mg calcium daily should be sufficient but adequate intestinal absorption of calcium depends on a normal level of vitamin d in the blood.