Every menstrual cycle is different. For some, periods come like clockwork, with identical symptoms from month to month. But for others, there might be some irregularity in timing and symptoms thanks to changes in daily schedule, travel or other factors.

But if you’re noticing an increasing fluctuation in the timing and length of your cycle, or in the severity of your symptoms, your irregular period may be a sign of an underlying issue.

Below, we explain what an irregular period is, what can cause irregular periods and when you should talk to your doctor or clinician.

What is an irregular period exactly?

Typically, menstrual cycles can last anywhere between 21 and 35 days, with periods lasting somewhere between two and seven days. And at some point, you’ll probably experience an irregularity in your cycle. Maybe your period comes earlier or stays a little longer, or perhaps your flow is heavier, or your cramps are more intense some months. That’s progesterone and estrogen, the main controllers of the menstrual cycle, at work.

These hormones can be affected by a variety of lifestyle and health factors, which can cause your cycle or period symptoms to fluctuate. This kind of slight irregularity is considered very normal. But there are some signs of an irregular period that could mean something more serious is going on. Keep reading to learn more.

Symptoms of irregular periods

Some fluctuation in your cycle and period is common. But if you experience any of these symptoms, your period may be considered irregular:

  • Your periods occur fewer than 21 days or more than 35 days apart
  • Your periods vary in timing by more than 20 days
  • Your periods consistently last longer than seven days
  • Your period pain becomes severe
  • You start bleeding more heavily than usual
  • You bleed between periods
  • You go more than 90 days without a period (and aren’t pregnant)
  • You have irregular periods and want to get pregnant

These signs of an irregular period could be due to an external cause such as stress or taking birth control, but it could also be caused by an underlying condition. Keep reading to learn more about potential causes.

Everyday causes of an irregular period


Changes in hormone levels are normal at the beginning and end of your menstruating years. Teenagers can often have irregular periods for the first year or two of puberty as their bodies start making more hormones than they’re used to. Similarly, estrogen and progesterone levels eventually start to decrease with age, usually between ages 40-50, making irregular periods one of the first symptoms of menopause.


When we’re stressed, our bodies produce cortisol, which can affect hormone production. How much of an affect depends on the amount of stress.

For example, a sudden burst of stress may mean your period is delayed a few days, while prolonged, severe stress may cause increasing irregularity and even stop your period for a time.

Taking steps to manage stress – such as eating well, exercising regularly, working on your mental health and practicing good sleep hygiene – can help a lot.

Birth control and other medications

You may already know that hormonal birth control methods use estrogen, progestin (synthetic progesterone) or a combination of the two to prevent ovulation. Because of this, one of the benefits of taking birth control pills or having a long-acting reversible contraceptive, like an intrauterine device (IUD), is that they can help balance hormones for many people, making menstrual cycles more regular.

However, it’s also possible for hormonal birth controls to cause some cycle irregularity. This is most common right after starting or stopping birth control. It may take several months after stopping birth control for your periods to become regular again.

Additionally, some other medications can cause irregular periods, such as anti-epilepsy and anti-anxiety medications.

Breastfeeding and lactation

Breastfeeding and lactation can impact your menstrual cycle. For instance, people who don’t produce their own milk for their child can usually expect their period to return sooner than those who do.

Why irregular periods are common while breastfeeding

Prolactin, the hormone responsible for milk production, suppresses the production of luteinizing hormone, a hormone that triggers ovulation. So the more your baby breastfeeds or the more you pump, the more prolactin is produced, and the more likely it is that your period will be irregular or suppressed. Your period will start to return to normal as you gradually wean your baby from breastfeeding or you begin to scale back from pumping.

Energy deprivation

If your body doesn’t get enough energy – either because you’re not eating enough, you’re exercising excessively, or a combination of the two – it may make changes to conserve energy. One of those changes could be an irregular period, or a complete stop to your period until there’s enough energy in your body for it to start again.

This can be especially common in female athletes (so common it has a name: the female athlete triad), but it can happen to anyone under the right circumstances. Your period may also become irregular if you suddenly start an intense exercise program or suddenly gain or lose a lot of weight.

In these situations, we strongly recommend that people talk with their primary care clinician or women's health specialist about other symptoms they may be experiencing and their diet and exercise regimen. Doctors can also refer their patients to specialists in a range of fields such as nutrition, women’s sports medicine, mental health and more.


When irregular periods could be a sign of a medical condition

Again, some fluctuation in your cycle and period is common. But in some cases, consistent or increasingly irregular periods may be one of several symptoms of an underlying condition. Some conditions that can have irregular periods as a symptom, include:

Polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a relatively common hormonal disorder. In addition to irregular periods, there are two main symptoms of PCOS: excess androgen (a male hormone that can cause facial and body hair growth, acne and thinning scalp hair) and enlarged ovaries containing fluid-filled sacs that surround the eggs.

A pelvic exam, ultrasound and blood tests are often used to diagnose PCOS.

Thyroid conditions

The thyroid is responsible for producing hormones that control our metabolism, or how our bodies use energy. When the thyroid doesn’t function properly, it’s referred to as overactive (hyperthyroidism) or underactive (hypothyroidism). Both of these conditions can cause irregular periods, but other symptoms vary.

Hyperthyroidism causes the body to burn energy faster. Symptoms can include anxiety, weight loss, rapid or irregular heartbeat, and lighter periods. In contrast, hypothyroidism slows down the body’s energy use. Symptoms may include fatigue, unexplained weight gain, forgetfulness, and frequent, heavy periods.

Thyroid conditions typically develop slowly, and many symptoms overlap with those of other conditions. If a thyroid condition is suspected by a doctor, blood tests can check the levels of thyroid hormones.

Uterine polyps

Uterine polyps are growths that form in the lining of the uterus, also known as the endometrial tissue. They’re most common during or after menopause. Uterine polyps are usually noncancerous and can be present without symptoms.

When symptoms are present, they commonly include heavy, irregular periods, bleeding or spotting between periods, infertility and vaginal bleeding after menopause.

A doctor may use a transvaginal ultrasound or hysteroscopy (inserting a thin, flexible telescope into the uterus) to identify polyps.


Endometriosis is a condition where tissue that’s similar to the uterine lining grows outside the uterus. It doesn’t generally affect the timing of your cycle, but it can affect your period symptoms and your fertility.

Pain is the most common symptom of endometriosis. It can come in various forms, including extremely painful menstrual cramps, pain when urinating during periods, and chronic lower back and abdominal pain that gets worse during periods.

To diagnose endometriosis, a doctor may perform a pelvic exam and use one or more imaging tests.

Pelvic inflammatory disease

Pelvic inflammatory disease (PID) can occur when bacteria moves from the vagina to the uterus, fallopian tubes or ovaries to cause an infection. PID is most often caused by gonorrhea or chlamydia, but in some cases it can be caused by normally occurring bacteria in the vagina.

PID often doesn’t have symptoms. But when it does, symptoms can include irregular periods, lower abdominal pain, pain during sex or urination, bad-smelling vaginal discharge and fever.

Getting a PID diagnosis may involve a physical exam, as well as tests for sexually transmitted infections (STIs) and urinary tract infections.

Primary ovarian insufficiency

Primary ovarian insufficiency (POI) is when the ovaries stop functioning properly before age 40. Some people with POI stop getting periods entirely, but others continue to get periods and are able to become pregnant.

For people with POI who still get periods, irregular periods are usually the first symptom. Other possible symptoms are similar to those of menopause, including hot flashes, decreased sex drive and vaginal dryness.

To diagnose POI, a doctor may test hormone levels and do a chromosome analysis. They may also use a pelvic ultrasound to look for structural issues in the ovaries.

When to see a doctor about irregular periods

Talk to a doctor or clinician if your periods seem more irregular than usual, or if your period comes with symptoms like the ones listed above. Even if it’s being caused by an everyday factor, your primary care provider, OB-GYN, midwife or another women’s health specialist can help diagnose it.

They can talk with you about your symptoms, perform tests and help diagnose the reason for your menstrual irregularities – then recommend treatment options tailored to you and your needs.