Two Periods in One Month: How Does This Happen?

The typical duration of menstruation is four to five days once every month, per the Centers for Disease Control and Prevention. However, some people may have two periods within a month's time.

Your menstrual cycle can be a reflection of certain aspects of your health—and having two periods in a month could be a sign of a problem that bigger than just picking up an extra box of pads or tampons.

Having Two Periods a Month

"Just because you have two periods that happen to land within the same calendar month doesn't mean there's a problem," said Mount Kisco, New York-based OB-GYN Alyssa Dweck, MD, author of "The Complete A to Z for Your V." That's because a normal menstrual cycle is between 21 and 35 days, according to the American College of Obstetricians and Gynecologists (ACOG). If your period came at the very beginning of this month and then showed up again at the end, this falls within a typical window.

And not everyone has a cycle that falls within this range. According to the National Institute of Child Health and Human Development, 14% to 25% of people have irregular periods. Irregular periods can signal a variety of different things. Cycles may be shorter or longer than normal, flows may be heavier or lighter than normal, and menstruation may be accompanied by other problems like cramps.

It's helpful to keep track of your cycle, so you know what normal means for you. If you're having a period that shows up more than once in 21 days, this is something that goes by the medical term polymenorrhea, or frequent menstruation. It is one of several ways a period can be irregular. But why does it happen?

Causes of Frequent Periods

If you're bleeding sooner than your normal cycle or spotting in between periods, there is a chance that it could be just a one-time irregularity. But if it's happening more than once, something else might be going on with your body.

A too-soon period may indicate a hormonal imbalance of estrogen, progesterone, or testosterone, which are all involved in ovulation. "This can cause irregular ovulation. Essentially, your uterus isn't sure when or how much to bleed," Dr. Dweck said.

For example, polycystic ovary syndrome (PCOS) can cause irregular bleeding. PCOS is a hormonal disorder that affects people of childbearing age. PCOS also puts people at higher risk of type 2 diabetes, high blood pressure, and endometrial cancer.

Here are a few other things to consider if you find that you're having another period sooner than expected.

Pregnancy

Pregnancy is one of the potential causes of bleeding twice in one month. "If you're sexually active, this is one of the initial things I think about. Some women experience irregular bleeding when pregnant," Dr. Dweck said.

Rest assured that irregular bleeding can be totally normal and not indicative that there's something wrong. Start by taking a pregnancy test and calling a healthcare professional; they'll let you know when they want you to come in for an appointment, Dr. Dweck recommended.

Puberty

During the teenage years of life, it's possible to have irregular periods after having your first one, according to the Office on Women's Health (OWH). This means that you might occasionally experience a second period in one month as your menstrual cycles start to become more regulated over time. According to ACOG, a typical teen menstrual cycle lasts between 21 and 45 days.

Perimenopause

Perimenopause could be a possible cause if you're around or over 40 years old. Perimenopause is a time when periods are known to be irregular, and you start going through the transition to menopause. "Perimenopause is a time when your hormones can be all over the place, ovulation can be sporadic, and you can get your period twice in a month," Dr. Dweck said.

Thyroid Function

Your thyroid, the gland that regulates your metabolism, can be another reason for your period showing up more than once. A thyroid that's over- (hyper-) or under- (hypo-) active can change up the frequency of your flow, Dr. Dweck said.

A 2020 review from the International Journal of Endocrinology and Metabolism explained that if your thyroid gland does not make enough hormones for your body, you could have heavier bleeding; if it makes too much, you could have lighter bleeding. If either of those two conditions remains unregulated, you can be liable to experience irregular periods or multiple periods in one month.

Other Potential Causes

Other structural problems, like uterine fibroids or polyps, may also bring on an additional bleed, and you can have breakthrough bleeding from an IUD or hormonal birth control pills, the ACOG noted.

When To See a Healthcare Professional

If you get your period more than once per month, contact a healthcare professional. "You can have a weird period episode, especially since stress, diet changes, travel, or exercise can cause irregularities, but if it's happening over and over, you should be seen by your doctor," Dr. Dweck explained.

A healthcare professional might also ask about whether you're also experiencing other symptoms or may run additional testing—blood work, ultrasound, etc.—depending on what's suspected. After that, the underlying cause will guide treatment. Examples of treatment include thyroid medication, a new birth control method, or a plan for managing PCOS.

A Quick Review

Figuring out why you're dealing with two periods in one month isn't always so cut and dry, but knowing why you might be having this experience will help you and the healthcare professional make a plan to manage any underlying problems.

Several different things could be causing bleeding that's too early. Cycles may become irregular when menstruating years are starting or nearing an end. Pregnancy is another factor that may cause a period twice a month. But thyroid function and structural problems could also be throwing your normal cycle out of whack.

Everyone's period is different, so it's important to know what normal means for you. Keep a record of your cycle to track when it starts, how long it lasts, and whether any symptoms like pain or cramping come with it. If you experience a period more than once within your normal cycle, contact a healthcare professional to find out what exactly is going on.