What Is an Irregular Period?

The 28-Day Myth and When to Worry

Your period is irregular

Verywell / Nusha Ashjaee 

There is a wide range of what is considered to be "normal" when talking about the menstrual cycle. That said, irregular periods can be a signal that something in the body is not quite right. For example, irregular periods can be an early sign of potential fertility problems in some people.

Knowing how to tell if your periods are irregular will help you understand your body better. Often, the term "irregular" may refer to a change in what's normal for you. Most women know what their typical cycle is like. Any persistent or concerning changes to that may warrant a visit to the gynecologist.

What Is an Irregular Period?

Irregular periods typically refer to the number of days between cycles counting from day 1 of your period to day 1 of the next period. Day 1 is traditionally the first day of actual flow. It's normal to have anywhere between 21 and 35 days between periods.

Your period is irregular if:

  • It comes more frequently than 21 days
  • The length of your cycles varies greatly (even if they are typically within the typical range of 21 to 35 days)
  • You go 35 days or more between periods

For example, if one cycle is 25 days, but another is 33 days, your cycles would be considered irregular (even though a 25- or 33-day cycle is otherwise normal).

It can also be normal for your cycles to vary by a few days from month to month. For example, your cycle could be 33 days one month and 35 days the next and not be cause for concern.

The 28-Day Myth

You may have heard that a 28-day cycle is normal. While a 28-day cycle could be considered the average cycle length, it's not necessarily an individual ideal.

The length of your menstrual cycle does not necessarily correspond to how fertile you are.

You could have a menstrual cycle that is longer or shorter than 28 days and still be fertile. Alternatively, you might have a textbook 28-day cycle and have fertility problems.

While irregular cycles can be a sign of a possible fertility problem, having regular cycles does not guarantee that your fertility is perfect. There are many causes of female and male fertility, and only some affect menstruation.

Occasional Irregular Periods

There are many factors that can influence an individual's menstrual cycle. Healthy individuals can experience a missed or irregular period if they:

  • Are breastfeeding (which in the early days may cause lactation amenorrhea or a total lack of periods)
  • Are pregnant
  • Are traveling (especially if their sleep pattern is interrupted or they are out of their normal time zone)
  • Are under a lot of stress
  • Experience illness

Excessive exercise and rapid weight loss can also lead to irregular or even absent periods. This is common in athletes. Some athletes don't know that their fertility can be impacted by exercise.

If you are overweight, losing weight might help make your periods more regular. If you are underweight, gaining weight can help restore and regulate your menstrual cycle (however, slow and steady weight change is the healthiest way to get there).

Other Period Irregularities

Even though the phrase "irregular periods" refers to cycle length, this is not the only aspect of your period that can go awry. You can have normal cycle lengths but experience:

Talk to your doctor if you are worried about any aspect of your menstrual cycle or have questions about your period, fertility, or reproductive health.

A Word From Verywell

Your period is one of the most easily observable aspects of your fertility. When you are trying to conceive, it can be helpful to keep a fertility calendar. Doing so lets you see if your periods are regular.

If you notice that your periods are not regular and you are having a hard time getting pregnant, it's something to tell your doctor about. Irregular cycles are sometimes a sign of a problem with ovulation. The good news is, ovulatory infertility can often be treated.

If your periods are regular but you still have not conceived, your doctor might have specific recommendations. They might encourage you to seek help for fertility if you don't get pregnant after one year of trying (or after six months, if you're age 35 or older).

Keep in mind that you can have regular "clockwork" periods and still have fertility problems.

Whether your periods are regular or not, talk to your doctor about any concerns you have related to your reproductive health. If you have worries, it's best to ask and receive reassurance than to ignore potential problems or fail to share a symptom that could help your doctor make a diagnosis.

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2 Sources
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  1. U.S. Department of Health and Human Services Office on Women's Health. Your Menstrual Cycle. Published March 16, 2018.

  2. U.S. Department of Health and Human Services Office on Women's Health. Period Problems. Updated March 16, 2018.