Why is my period late?

Wondering where your period is? It’s understandable if you’re feeling some concern about why your period is late. And it’s common for people to wonder if their late period means they’re pregnant.  But there are a number of reasons your period may be missing aside from the big one—pregnancy.

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The average adult menstrual cycle lasts 28 to 35 days, but your period can vary month to month, and some months may have a cycle that starts a few days later than the month prior. This is not an immediate reason for concern. 

However, some people experience periods that are consistently late or infrequent. Healthcare providers refer to this as oligomenorrhea. Those who deal with this condition typically have a cycle that is longer than 35 days, or fewer than six to eight periods per year (Riaz, 2021; Weld, 2021).

Rest assured, a late period doesn’t automatically mean that you have oligomenorrhea. For example, there are two times when it’s totally normal for someone’s period to be “late” or irregular: when it first begins, and when menopause starts. 

Here are some of the most common reasons a period may be late, and what it could be telling you about your health.

Pregnancy

If you’ve recently had unprotected sex (whether that be without protection or perhaps missing a few birth control pills), a late period could be the first sign of pregnancy (Riaz, 2021). 

If you suspect you might be pregnant and your period is late, an at-home pregnancy test can confirm this. If the test is positive, the next step should be making an appointment with your health care provider (Riaz, 2021).

Stress and strenuous exercise 

Once pregnancy has been ruled out, you may be scratching your head as to why your period is late. One reason may be due to excessive stress in your daily life. High stress levels are linked to irregular menstrual cycles and could delay your period (Nagma, 2015). 

Plus, low body weight and eating disorders like anorexia, as well as disturbed sleep patterns, are other reasons your period may be lagging (Ko, 2017; Xing, 2020). This means if stress causes you to skip meals or skimp on getting enough shut-eye, this could result in a late period.

Strenuous exercise can also cause late or even missed periods. When someone engages in excessive exercise and doesn’t eat enough, it can cause an energy deficiency by burning too many calories. In one study, strenuous exercise that created a calorie deficit of 470 to 810 calories a day over a three-month period caused late or irregular periods in those women (Williams, 2015).  

Periods typically go back to normal as soon as you make some lifestyle changes by lessening training intensity and eating normally to cause some weight gain.

Perimenopause

As the body begins the shift into menopause, periods may start to become irregular. Early in the transition to menopause, periods are often more frequent. Later, however, cycles become longer (Delamater, 2019).

While the patterns of menstrual bleeding do vary among those experiencing perimenopause, there are some telltale menopause signs you can watch out for: hot flashes, vaginal dryness, sleep disturbances, and mood changes could mean that you are shifting into menopause (Delamater, 2019).

A visit with your healthcare provider can help you determine if perimenopause is at the helm of your period problems.

Hormone disorders like PCOS

PCOS, or polycystic ovary syndrome, is a type of hormone disorder and is one of the more common ones responsible for a late or irregular period. That’s because, with PCOS, your ovaries produce excess androgens, a “male” sex hormone (while considered a male sex hormone, both men and women have androgens in the body, women just have smaller amounts). This surplus of androgens can cause irregular, late, or missed periods (Ajhmal, 2019).

There are other hormone disorders that may also cause irregular or late periods. Conditions like hyperthyroidism and hypothyroidism, diabetes, and Cushing’s syndrome (when the body produces too much of the stress hormone cortisol) may all affect your reproductive system (Naz, 2020).

Continuous birth control

In addition to preventing unwanted pregnancy, birth control pills or intrauterine devices (IUDs) may lighten, delay or stop your period. Some people who menstruate may choose to use continuous forms of hormonal birth control to reduce the duration or frequency of their periods or suppress them altogether. 

The long-term, continuous dose of hormones you receive from your birth control help to reduce spotting, irregular breakthrough bleeding, and the number of days you bleed during your cycle (Hee, 2013).

Pituitary tumors

The thought of having a tumor is scary, but pituitary tumors—clinically known as prolactinomas—are benign, noncancerous tumors located on the pituitary gland at the base of your brain—which can cause high levels of a hormone called prolactin (Kulshreshtha, 2017). 

This is the same hormone responsible for helping women lactate after pregnancy, and too much in the bloodstream may result in a late period due to a hormonal imbalance. When this happens, the condition is called hyperprolactinemia. Certain medications such as antipsychotic drugs can also cause hyperprolactinemia, resulting in late or irregular periods (Kulshreshtha, 2017).

Getting the proper treatment for a late period will vary depending on what is causing your period to be late to begin with. 

In some cases, a late period is a sign of an underlying health issue like PCOS. In order to prevent a late period, treating the condition causing the late period will help the menstrual cycle to stabilize. If a late period is due to lifestyle habits or issues such as stress or poor sleep, practicing good sleep hygiene, eating a healthy diet, and managing stress through meditation, mindfulness, and anything else that may calm your mind can help prevent late periods (ACOG , 2021). 

Oligomenorrhea itself usually isn’t a serious condition, but as we’ve learned above, it can sometimes be a symptom of other health issues. If your period is late because you had unprotected sex and you’ve confirmed pregnancy with an at-home test, it’s time to see your healthcare provider to go over what comes next. 

However, if you’re not pregnant, and have gone 35 days without a period, a healthcare provider can look at your full health history and determine what the next steps (if any) should be to address your late period (Riaz, 2021). 

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Current version

October 11, 2021

Written by

Colleen Travers

Fact checked by

Felix Gussone, MD

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About the medical reviewer

Felix Gussone, MD, Ro

Felix Gussone is a physician, health journalist and a Manager, Medical Content & Education at Ro.