What Is an Irregular Period?

The 28-Day Myth, Irregularity Beyond Menstruation, When Not to Worry

woman looking at calendar thinking about whether her period is irregular
When you see your doctor, bring the dates of your last three to six periods. They can use this information to determine if your periods are irregular or not. Image Source/Photodisc/Getty Images

Irregular periods can be a signal that something isn't quite right with your reproductive system. In fact, for some women, irregular periods are an early infertility symptom.

That said, there is also a wide range of normal.

Understanding what's considered irregular and what's not can help you understand your body. It can also help you better explain to your doctor your current state of reproductive health.What Is an Irregular Period?

When someone says they have an irregular period, they are typically referring to the number of days between cycles or the variation between periods.

Your period is considered irregular if the number of days between periods is either shorter or longer than the normal range.

So, your period is irregular if...

  • it comes more frequently than 21 days
  • you go 35 days or more between periods
  • the length of your cycles varies greatly (even if they are typically within the 21 to 35-day range)

For that last one, for example, if one cycle is 25 days, but another is 33 days, that would be considered irregular. This would be irregular even though a 25 or 33-day cycle is normal otherwise.

It is normal if your cycles vary by just a few days from month to month. For example, if one month it's 33 days, and another it's 35 days, that's okay. 

The 28-Day Myth

You may have heard that a 28-day cycle is normal. If your cycle is shorter or longer than 28 days, you might worry your periods are irregular.

This is a common myth.

A 28-day cycle may be the average cycle length. But you shouldn't think it's the ideal.

Your cycle can be longer or shorter than this and you can still have great fertility.

Something else you need to know: you can have a textbook 28-day cycle and have fertilty problems!

    An Occasional Irregular Period Can Be Normal

    If your periods are frequently irregular, this may signal a problem.

    On the other hand, an occasional irregular period can be normal.

    A healthy individual may have a missed or irregular period if they...

    • experience illness, including the flu or bad cold
    • are under a lot of stress
    • are traveling, especially if their sleep patterns have been thrown off
    • are breastfeeding, which in the early days may cause lactation amenorrhea (a total lack of periods)
    • are pregnant

    Excessive exercise can lead to irregular or even absent periods. This is common in athletes. 

    Some athletes don't know that their fertility can be impacted by their exercise regimen.

    If you're an athlete and you want to get pregnant, you may need to cut back to restart your periods and ovulation.

    Also, you may experience irregular periods if you lose or gain a significant amount of weight.

    This is a "normal" reaction, but this doesn't mean that extreme weight loss or gain is good for your health.

    For women who are overweight, losing weight may regulate the menstrual cycle. For women who are underweight, gaining some weight can help regulate things.

    Irregularity Beyond Menstrual Cycle Length

    Even though the phrase "irregular periods" refers to cycle length, you shouldn't think this is the only aspect of your period that can go awry.

    You can have normal cycle lengths but experience...

    • abnormal spotting
    • too heavy or too light bleeding
    • severe cramps
    • extreme mood swings
    • or other abnormal period symptoms

    If you're concerned about any aspect of your period being irregular, speak to your doctor.

    It's better to ask and receive reassurance that all is well than ignore a potential problem or fail to share a telling symptom that could help your doctor make a diagnosis.

    More on getting pregnant with infertility:


    Menstruation and the Menstrual Cycle. WomensHealth.gov. Accessed June 2, 2011. http://www.womenshealth.gov/faq/menstruation.cfm

    Menstrual periods - Heavy, Prolonged, or Irregular. MedlinePlus. Accessed June 2, 2011. http://www.nlm.nih.gov/medlineplus/ency/article/003263.htm. Link expired.

    Normal Menstruation. ClevelandClinic.com. Accessed June 2, 2011. http://my.clevelandclinic.org/anatomy/female_reproductive_system/menstruation/hic_normal_menstruation.aspx

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