context: Girls usually get their first menstrual period when they're 12 or 13. It's a sign that your body is maturing, so that one day, if you want to, you should be able to have a baby. By age 15, 98% of teens have started their periods. If you're not one of them, make an appointment to talk to your doctor. She can ask you and a parent about your family history, daily activity level, and examine you to figure out the causes for your delay. The reasons may be nothing to worry about. Or they could be a sign that you have a health condition that you need to treat. If your mom didn't get her period until she was 15 or older, chances are that being a late bloomer runs in your family. That may especially be true if your aunts, grandmothers, and cousins also started menstruating only after they were well into high school. Girls tend to get their periods 2-3 years after their breasts start to develop and 6-12 months after they notice a mucus-like vaginal discharge in their underwear. All these milestones can happen later than average in some families, including yours. Still, your doctor may want to rule out other health problems. If you weigh much less than normal, that can affect your hormone levels and prevent you from getting your period. If your weight is 10% less than what's healthy for your height, it can keep your hormones from working right and actually stop your periods. This is why girls who have eating disorders like anorexia or bulimia may not start menstruating. If you're obese, you may not have your first period at the usual time, either. To set a monthly menstrual cycle, your body needs a normal range of fat levels. Too much or too little body fat can lead to delayed periods. Obesity for someone 5 feet, 2 inches tall starts at 155 pounds. Pushing your body too hard physically also can make your first period come late. This can happen with ballet dancers, runners, or other athletes. Intense workouts burn lots of calories and can leave very little body fat. Mix that with competitive pressure, and they can postpone your period until you're well into high school. It can be hard on your body in many ways, and one possible effect is to delay your first period. This may happen if you're stressed all the time, no matter if it comes from too much homework, family problems, intense sports training, or other issues. Certain types of drugs can keep you from having a period, including those used to treat cancer, high blood pressure, allergies, and depression. If you're taking any of them, your doctor may have explained that this could happen. Very rarely, you may not be able to have periods because of the shape or other issues with your vagina, ovaries, fallopian tubes, or uterus. You might have extra tissue that covers an opening, a blockage, or physical issues. Your doctor can find out if these problems may be the reason. Conditions that may be behind your delayed periods include: Problems with a part of your brain called the hypothalamus, or a nearby organ called the pituitary gland. They work together to control your hormones Polycystic ovary syndrome, which causes your hormones to get out of balance Genetic conditions like fragile X syndrome, Turner syndrome, or androgen insensitivity syndrome