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How long does a normal menstrual cycle last?

A menstrual cycle is the period of time from day one of your menstrual period to day one of your next period. Menstrual cycles may occur at the same time each month or be irregular. Typically, a cycle occurs about once a month, but can be as short as 21 days or as long as 35 days and still be considered normal. Menstrual flow lasts about 3 to 7 days.

When is it considered late?

A menstrual period is considered late if it is 5 or more days overdue according to your usual pattern of periods. A period is considered missed if there is no menstrual flow for 6 or more weeks.

What is the cause?

A late or missed period could be caused by any of the following:


This is the most common cause of missed periods in teenage girls. If you have had sex even once in the past several months, see your healthcare provider for a pregnancy test before you consider any of the other possible causes.

A positive pregnancy test is the only way to be certain of pregnancy. It is best to see your healthcare provider for a pregnancy test. Home test kits can be confusing and give misleading results. It also helps to have a supportive person who can answer your questions if you are pregnant. You may wish to have a parent (or other adult you trust) go with you. Breast swelling, weight gain, and nausea are also signs of pregnancy.

It is important to find out early if you are pregnant. You need to look at the options and start prenatal care if you plan to have the baby. Early prenatal care helps ensure a healthy baby. You will not have a normal period until after the baby is born.


Stress is the second most common cause of late or missed periods in teenagers. It may be emotional stress (for example, breakup with a boyfriend or final exams) or depression. Or it may be physical stress to the body, such as a severe illness, a sexually transmitted disease, rapid weight loss or gain, or strenuous exercise. Dieting or binging and purging may interrupt menstrual cycles. Changes in your usual routine (for example, going on vacation) may also cause your period to be late or missed.

Some stress is a normal part of daily life. Only you can know if you are under too much stress. Your periods should return when the activities or situations that are stressing you are eliminated or changed.

Normal development

During the first couple of years of menstruation many teenagers have irregular periods. During this time the body’s hormones are not yet “fine-tuned,” so the ovaries may not release an egg once every month. As a result, your cycles may be irregular, occurring as close together as 2 weeks or as far apart as 3 months.

If you’ve been having periods for 2 years or less and your physical exam is normal, your irregular periods may be part of your normal development. Remember, if you have had sex, go to your doctor’s office for a pregnancy test when your period is late for you, even if you normally have irregular cycles. There are many ways to prevent pregnancy when you are having sexual intercourse. Some birth control methods work better than others. You need to consider whether the method you choose will also protect you from getting sexually transmitted diseases (STDs). Ask your healthcare provider to help you decide which method may be right for you.

Most girls’ menstrual cycles become fairly regular as their hormone levels mature and synchronize. A few women will continue to have irregular cycles as their normal pattern.

Hormone imbalance

Hormone imbalance is rarely the cause of missed periods. Though rare, polycystic ovary syndrome is the most common type of hormone imbalance that affects the menstrual cycle in teenagers. Polycystic ovaries may cause irregular cycles, increased body hair, acne, and weight gain.

Sometimes when you stop taking birth control pills you may have a temporary hormone imbalance and loss of periods. If you are having sex, be sure to use another reliable method of birth control because you could still become pregnant.

If you have missed several periods without an explanation, your doctor can check your ovaries and look for any signs of hormone imbalance. Blood tests can be done to measure hormone levels. Most often a hormone imbalance can be treated.

Problems of the thyroid gland, pituitary gland, adrenal glands, or ovaries can be rare causes of irregular periods.

How can I take care of myself?

  1. Mark on a calendar when your periods occur and how long they last. This information can help your doctor make a correct diagnosis. Take it to your appointment.
  2. Eat healthy foods and keep your weight steady. If you are overweight, a balanced diet and regular exercise will help you lose weight slowly (no more than 2 pounds a week). Talk with your healthcare provider if you are not sure what your proper weight should be, or if others are worried about your weight.
  3. If you follow a strenuous exercise program, consider cutting back until your periods come back.
  4. If you have sex, always use birth control. Talk to your doctor about the available methods.
  5. If you think you might be pregnant, get a pregnancy test if your period is 5 or more days late. Don’t wait. You can get confidential testing and counseling in most doctors’ offices and clinics. Take your first morning urine specimen with you for the test. Keep it refrigerated until you take it in.
  6. Consider counseling if you are stressed out.

When should I call my healthcare provider?

Call during office hours if:

  • You think you might be pregnant.
  • Your period is at least 5 days late and you have had sex.
  • Your period does not return within 6 weeks.
  • You need help with gaining or losing weight.
  • You need help for binging and purging or extreme dieting.
  • You need help for stress or depression.
  • You have an abnormal vaginal discharge or abdominal pains.
  • You develop a lot of face or body hair, bad acne, trouble seeing, headaches that won’t go away, a deeper voice, coarse skin, or if you feel hot or cold when no one else does.
  • Your period does not return within 6 months after stopping birth control pills and you aren’t pregnant.
  • You have other questions or concerns.

Written by Kathleen A. Mammel, MD, Director, Adolescent Pediatrics, William Beaumont Hospital, Royal Oak, Michigan. Published by RelayHealth.
Last modified: 2009-12-10
Last reviewed: 2010-10-04 This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional. References
Pediatric Advisor 2011.4 Index
© 2011 RelayHealth and/or its affiliates. All rights reserved.