Menstrual Cycle

A menstrual cycle begins when you get your period or menstruate. This is when you shed the lining of your uterus. This cycle is part of your reproductive system and prepares your body for a possible pregnancy. A typical cycle lasts between 24 and 38 days.

Female Reproductive Organs
Female Reproductive Organs

What is menstruation?

Menstruation is the monthly shedding of the lining of your uterus. Menstruation is also known by the terms menses, menstrual period, menstrual cycle or period. Menstrual blood — which is partly blood and partly tissue from the inside of your uterus — flows from your uterus through your cervix and out of your body through your vagina.

Menstruation is driven by hormones. Hormones are chemical messengers in your body. Your pituitary gland (in your brain) and your ovaries (part of your reproductive system) make and release certain hormones at certain times during your menstrual cycle.

These hormones cause the lining of your uterus to thicken. This happens so that if a pregnancy would occur, an egg can implant into your uterine lining. Hormones also cause your ovaries to release an egg (ovulation). The egg moves down your fallopian tubes, where it waits for sperm. If a sperm doesn’t fertilize that egg, pregnancy doesn’t occur. The lining of your uterus breaks down and sheds. This is your period.


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What is a menstrual cycle?

The menstrual cycle is a term to describe the sequence of events that occur in your body as it prepares for the possibility of pregnancy each month. Your menstrual cycle is the time from the first day of your menstrual period until the first day of your next menstrual period. Every person’s cycle is slightly different, but the process is the same.

How long is a normal menstrual cycle?

The average length of a menstrual cycle is 28 days. However, a cycle can range in length from 21 days to about 35 days and still be normal.

How many days between periods is normal?

The days between periods is your menstrual cycle length. The average menstrual cycle lasts 28 days. However, cycles lasting as little as 21 days or as long as 35 days can be normal.


How long does a normal period last?

Most people have their period (bleed) for between three and seven days.

Is a three-day period normal?

A period is normal if it’s anywhere between three and seven days. While on the shorter end of the range, some people have a menstrual period for three days. This is OK.

What are the four phases of the menstrual cycle?

The rise and fall of your hormones trigger the steps in your menstrual cycle. Your hormones cause the organs of your reproductive tract to respond in certain ways. The specific events that occur during your menstrual cycle are:

  • The menses phase: This phase begins on the first day of your period. It's when the lining of your uterus sheds through your vagina if pregnancy hasn’t occurred. Most people bleed for three to five days, but a period lasting only three days to as many as seven days is usually not a cause for worry.
  • The follicular phase: This phase begins on the day you get your period and ends at ovulation (it overlaps with the menses phase and ends when you ovulate). During this time, the level of the hormone estrogen rises, which causes the lining of your uterus (the endometrium) to grow and thicken. In addition, another hormone — follicle-stimulating hormone (FSH) — causes follicles in your ovaries to grow. During days 10 to 14, one of the developing follicles will form a fully mature egg (ovum).
  • Ovulation: This phase occurs roughly at about day 14 in a 28-day menstrual cycle. A sudden increase in another hormone — luteinizing hormone (LH) — causes your ovary to release its egg. This event is ovulation.
  • The luteal phase: This phase lasts from about day 15 to day 28. Your egg leaves your ovary and begins to travel through your fallopian tubes to your uterus. The level of the hormone progesterone rises to help prepare your uterine lining for pregnancy. If the egg becomes fertilized by sperm and attaches itself to your uterine wall (implantation), you become pregnant. If pregnancy doesn’t occur, estrogen and progesterone levels drop and the thick lining of your uterus sheds during your period.


At what age does menstruation typically begin?

People start menstruating at the average age of 12. However, you can begin menstruating as early as 8 years old or as late as 16 years old. Generally, most people menstruate within a few years of growing breasts and pubic hair.

People stop menstruating at menopause, which occurs at about the age of 51. At menopause, you stop producing eggs (stop ovulating). You’ve reached menopause when you haven’t gotten a period in one year.

What are symptoms of getting your period?

Some people experience symptoms of menstruation and others don’t. The intensity of these symptoms can also vary. The most common symptom is cramps. The cramping you feel in your pelvic area is your uterus contracting to release its lining.

Other signs you’re getting your period are:

  • Mood changes.
  • Trouble sleeping.
  • Headache.
  • Food cravings.
  • Bloating.
  • Breast tenderness.
  • Acne.

How does your period change over time?

Your menstrual cycle can change from your teen years to your 40s or 50s. When you first get your period, it’s normal to have longer cycles or a heavier period flow. It can take up to three years for young people to have regular cycles after they begin menstruating. A normal menstrual cycle is a cycle that:

  • Occurs roughly every 21 to 35 days.
  • Causes bleeding for between three and seven days.

Once you reach your 20s, your cycles become more consistent and regular. Once your body begins transitioning to menopause, your periods will change again and become more irregular.

It’s also normal for your period to change during other life events that affect your hormones, such as after childbirth or when you’re lactating.

What is considered an irregular period?

Irregular menstruation describes anything that’s not a normal menstrual period. Some examples of an irregular period are:

  • Periods that occur less than 21 days or more than 35 days apart.
  • Not having a period for three months (or 90 days).
  • Menstrual flow that’s much heavier or lighter than usual.
  • Period bleeding that lasts longer than seven days.
  • Periods that are accompanied by severe pain, cramping, nausea or vomiting.
  • Bleeding or spotting that happens between periods.

How much should I bleed during my period?

You can expect to lose between two and three tablespoons (tbsp.) of blood during your period. Some signs of irregular period bleeding are:

  • Bleeding through a tampon or pad every one to two hours.
  • Passing blood clots larger than a quarter.
  • Bleeding longer than seven days each time you have your period.

It’s normal to experience some variation in the amount of bleeding each cycle. It’s also important to remember your normal may be different than someone else’s. Try not to compare. Talk to a healthcare provider if you’re concerned about irregular or severe bleeding during your period.

How do I track my period?

It’s a good idea to be aware of your menstrual period. Not getting a period may not seem like a big deal, but an irregular period can be a sign of a problem. Your healthcare provider will ask you about your most recent period and menstrual cycles. Knowing what’s normal for you can be very helpful to your provider.

Tracking your period can also be helpful in knowing when you ovulate, which is when you’re most likely to get pregnant. It can also help you plan ahead or prepare for period bleeding during a special event or vacation.

To track your period:

  • Mark the first day of your period on a calendar with an X. This is day one.
  • Continue to mark each day you’re bleeding with an X. Stop marking when your bleeding stops.
  • When bleeding starts again, mark it with an X. This is day one again.
  • You can then count the number of days between each first X to get the length of your cycle. Count the number of X’s to see how many days bleeding lasts.

There are also apps that do all of this for you that you can download on your phone or tablet.

When should I worry about my period?

Contact your healthcare provider if:

  • You haven’t had a period by the age of 16.
  • You don’t get your period for three months or longer.
  • You’re suddenly bleeding for more days than usual.
  • You’re bleeding much lighter or much heavier than usual.
  • You have severe pain during your period.
  • You have bleeding between periods.
  • You feel sick after using tampons.
  • You think you might be pregnant — for example, you’ve had sex and your period is at least five days late.
  • Your period hasn’t come back within three months of stopping birth control pills and you know you’re not pregnant.
  • You have any questions or concerns about your period or possible pregnancy.

A note from Cleveland Clinic

Your menstrual cycle provides valuable insight to your healthcare provider about your reproductive health. A normal menstrual cycle can last between 21 and 35 days. You can expect to bleed between three and seven days each time you get your period. Contact your healthcare provider if you have questions or concerns about your menstrual cycle. In some cases, an irregular cycle could mean you have a health condition that needs treatment.

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Medically Reviewed

Last reviewed on 12/09/2022.

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