Menstruation typically works on a monthly cycle. It’s the process a woman’s body goes through as it prepares for possible pregnancy. During this process, an egg will be released from the ovaries. If that egg isn’t fertilized, the lining of the uterus is shed through the vagina during a woman’s menstrual period.

Your period, also known as menstruation, typically lasts anywhere from two to eight days.

Many women experience symptoms during their period. Certain symptoms like cramping or mood changes can begin before the actual period. This is often called premenstrual syndrome, or PMS. Most women’s menstrual symptoms resolve after the period is over.

The full menstrual cycle is counted from the first day of one period to the first day of the next. It typically lasts between 21 and 35 days. There are different stages within the menstrual cycle. These include:

The follicular phase

The follicular phase starts on the first day of menstruation and ends when ovulation begins. During this stage, the ovaries produce follicles, which then house eggs. This stimulates the thickening of the uterus’s lining. There’s an increase in estrogen during this time.

Ovulation

The mature egg is released into the fallopian tube and then the uterus. This typically occurs about two weeks into a woman’s cycle, or about midway.

The luteal phase

The body maintains its preparation for pregnancy. This includes an increase of progesterone and a small amount of estrogen. If a fertilized egg doesn’t implant in the uterus, this phase will end and menstruation will begin. In a 28-day cycle, this phase ends around day 22.

Menstruation

During this stage, the thickened lining of the uterus is shed during a woman’s period.

Many women will experience irregular periods at some point in their lives. It’s particularly common for young women to experience highly irregular periods — including very long periods — during their first few years of menstruation. Their periods will often shorten and stabilize between one and three years after menstruation begins.

Irregular periods include periods that are lighter, heavier, arrive unpredictably, or last longer or shorter than the average. According to the Eunice Kennedy Shriver National Institute of Child Health and Human Development, it’s estimated that between 14 to 25 percent of women have what are classified to be “irregular” cycles.

That being said, if your periods are less than 21 days apart or more than 35 days apart, there could be an underlying cause that’s making you more irregular. If this is the case, make an appointment with your doctor.

There are a number of different factors that affect your cycle. As you get older, for example, your period will get lighter and become more regular.

Using a new contraceptive, including birth control pills, vaginal rings, and IUDs, can make you irregular at first. Many birth control methods can cause long, symptomatic periods for the first one to three months after you start taking them, but these even out over time.

Other factors that can make you irregular, or cause changes to your menstrual cycle, include:

  • extreme weight loss
  • excessive exercising
  • infections to the reproductive organs, like pelvic inflammatory disease (PID)
  • conditions like polycystic ovarian syndrome (PCOS)
  • increased stress
  • changes in diet

Many women prefer to regulate their menstrual cycle. Doctors may even recommend it for women whose periods are consistently irregular.

Regulating the menstrual cycle focuses on strategies and treatments to ensure that a woman’s period comes within a set frame of time and lasts for a time frame between the “normal” two to eight days.

The most common way to regulate your menstrual cycle is through birth control pills, or other similar hormonal contraceptives like the patch or the NuvaRing. Some of these contraceptive methods will trigger a woman’s period once a month, while others may only give her a period once every three or six months.

Other methods of regulating the menstrual cycle could involve treatment for eating disorders that are causing severe weight loss, or modifying diet and lifestyle. If you’re able to reduce stress, that could also reduce irregularity of your period, too.

While every woman is a little different and her “normal” will be unique, there are symptoms that indicate it’s a good idea to talk to your healthcare provider. These symptoms include:

  • Your period becomes irregular after it’s been steady and predictable for a long time.
  • Your periods suddenly stop for 90 days or more and you aren’t pregnant.
  • You think you may be pregnant.
  • Your period lasts for more than eight days.
  • You bleed much more heavily than usual.
  • You soak through more than one tampon or pad every two hours.
  • You suddenly begin spotting.
  • You develop severe pain during your period.
  • Your periods are more than 35 days apart, or less than 21 days apart.

If you suddenly get a fever and experience flu-like symptoms after using tampons, seek immediate medical attention. These symptoms could indicate a dangerous complication called toxic shock syndrome.

When asking how long your period lasts, it’s easy for women to want a definitive answer. Each woman is different, however, and she’ll have her own normal. Tracking your unique cycle each month will help you detect trends and patterns, so you’ll notice any changes as soon as they happen.

If you’re experiencing any sudden changes in your period that you don’t believe are stress-related, especially alongside other new symptoms, you can always make an appointment with your gynecologist to double check.