For most women, menstrual cycles last between 21 and 35 days, with a period of three to seven days. However, many women experience variations in the length, timing, and symptoms of their cycles, and menstrual disorders are often to blame. Up to 85 percent of women with regular cycles experience at least one menstrual disorder symptom before their periods.

Your menstrual cycle isn’t always like clockwork. While some women get their periods right on schedule every 28 days, other women’s cycles aren’t so predictable.

“At least 30 percent of women have irregular periods during their childbearing years,” says Amy Autry, MD, a clinical professor of obstetrics-gynecology and reproductive sciences at the University of California, San Francisco. While an irregular cycle is not usually a problem, it can occasionally signal health complications.

Menstrual periods are often irregular during the first few years after menstruation starts. It may take several years for the hormones that control menstruation to reach a balance.

When Is a Period Irregular?

A normal menstrual cycle lasts 28 days, plus or minus seven days. Menstrual bleeding is considered irregular if it occurs more frequently than every 21 days or lasts longer than 8 days. Missed, early, or late periods are also considered signs of an irregular cycle.

To determine whether your menstruation schedule is irregular, count from the last day of your previous period and stop counting on the first day of your next. Repeat this for three months. “If the number of days between stopping and starting your period is significantly different each month, you have an irregular cycle,” says Dr. Autry.

Causes of Irregular Periods

In many cases, irregular periods are related to a condition called anovulation. “This means that ovulation hasn’t taken place during your menstrual cycle, usually due to severe hormonal imbalances,” says Autry.

Sometimes an irregular period may be due to subtler hormone imbalances. You may still be ovulating, but the timing of your ovulation can vary greatly month to month. This is because lifestyle and medical conditions can influence your menstrual cycle.

Pregnancy is the most common cause of a missed period. If you might be pregnant, treat yourself as if you are pregnant until you know for sure. Use a home pregnancy test as the first step to finding out whether you are pregnant.

The following factors can trigger irregular or missed periods:

Extreme exercise or dieting. Exercising too much can throw off the timing of menstrual bleeding and sometimes stop it. “It’s common for endurance athletes to have missed periods,” says Autry. Being underweight, whether from extreme exercise, dieting, an eating disorder, or illness, can have the same effect.


Stress. Chronic stress or even short-term anxiety about a specific problem can wreak havoc with your hormone balance, causing a missed period and irregular cycle.

The pill.Birth control pills can make your periods lighter, or cause you to miss periods or have less or more frequent periods — or even no periods at all.

Polycystic ovary syndrome (PCOS). This medical condition causes tiny cysts to form on ovaries, interfering with regular ovulation. Women with PCOS usually have a history of irregular periods. In addition to causing infertility, PCOS can increase the risk of diabetes and heart disease.

Other illnesses. Thyroid disorders can cause irregular periods if blood levels of the thyroid hormone go too low or too high. Other health conditions that may cause an irregular cycle include sexually transmitted diseases, diabetes, fibroids, eating disorders, and endometriosis.

Age. When teens first start having periods, their menstrual cycles may not always be on the same schedule every month. It may take several years to settle into a pattern. In addition, missed periods and lighter or heavier periods are common as women near menopause.

When Should You Be Concerned About an Irregular Period?

A missed or irregular period may be the first clue that you have a condition that needs medical attention. “If you have consistently irregular periods, you should be evaluated for PCOS,” says Autry. “PCOS affects up to 10 percent of women of reproductive age.”

You should also be screened for thyroid disorders and other diseases that may be linked to irregular periods.

An irregular cycle can also make it more difficult to get pregnant, especially if you’re not ovulating every month. Your doctor can run tests to see if you’re ovulating. Women with irregular periods who are trying to have a baby are sometimes prescribed fertility drugs to increase ovulation. “While it’s possible to get pregnant on your own if you have irregular periods, it’s still a good idea to be checked out by a doctor just to make sure that nothing serious is going on,” recommends Autry.

Prevention and Treatment of Irregular Periods

If stress is a possible culprit in your irregular cycle, try stress management techniques, such as meditation, yoga, tai chi, visualization, and biofeedback. Avoid over-exercising and try not to diet excessively, as doing so can interfere with your menstrual cycle.

Oral contraceptive pills may be prescribed to get your period back on track. But if you’d rather travel the natural treatment road, consider black cohosh. This medicinal herb is sometimes used for menstrual irregularities and premenstrual syndrome, though rigorous scientific studies haven’t verified these properties. Black cohash should not be used if you have any symptoms of or a past history of liver disease.

You may have heard that completely darkening your room at night will help regulate menstrual cycles — but whether it really works is unknown.

A couple of irregular periods per year are usually nothing to worry about. Any more than that, and you should see a doctor to be sure an ovulation problem or health condition isn’t the cause. However, you might want to rule out pregnancy first. “If you’ve had sexual relations in the past month, take a home pregnancy test first,” advises Autry. If the test is negative, then you can explore other options and talk to your doctor about how to get your menstrual cycle back on track.


Remember, you can still become pregnant even though you are not menstruating. Practice birth control if you do not wish to become pregnant.

Premature ovarian failure is when you stop menstruating before age 40. Surgery, chemotherapy, and radiation therapy to the abdomen or pelvis may cause premature ovarian failure.

Other diseases such as irritable bowel syndrome, tuberculosis, liver disease, and diabetes can cause missed or irregular periods, although this is rare. But if any of these diseases are present, you will usually have other symptoms besides menstrual irregularities.

If you've skipped a period, try to relax. Restoring your life to emotional and physical balance can help. Many women miss periods now and then. Unless you are pregnant, chances are your cycle will return to normal next month.

Missed or Irregular Periods - Check Your Symptoms

Call a doctor if:

• You have lower belly pain and think you could be pregnant.
• A home pregnancy test says you are pregnant, or you think you're pregnant even though the test says you are not.
• You have missed two regular periods and don't know why.
• You miss two periods while taking birth control pills, and you have not skipped any pills.
• You have not had your first period by age 16.
• You have not developed breasts or pubic hair by age 14.