The menstrual cycle is a hormonal process where the body prepares for pregnancy.

Fast Facts:

  • A normal menstrual cycle is 21-35 days in adults. An adolescent may have a larger range of 21-45 days.
  • PMS is your body's reaction to the changing hormone levels in your body. Some people are more sensitive to this than others.
  • It's common to have irregular periods when menstruation begins.
  • If you had unprotected sex or a birth control failure and you don't want to get pregnant, you can use emergency contraception.


As people with vaginas go through puberty, they begin to have periods and menstrual cycles. The menstrual cycle is a hormonal process where your body prepares itself for pregnancy. Your period is one part of the menstrual cycle. Menstruation is the process of having periods from puberty until menopause, when periods stop occurring.

The Menstrual Cycle

A typical cycle lasts around 28 days, but most people do not have regular cycles. A normal menstrual cycle (counting from the first day of one menstrual period to the first day of menses of the next cycle) is 21 to 35 days in adults. As an adolescent, there may be a slightly larger range of 21 to 45 days. The larger range is typically seen up to two years after menarche (your first period).

The menstrual cycle starts on the first day of menstruation (aka your period). During your period, your body gets rid of its uterine lining (or endometrium). The uterine lining builds up over the course of the menstrual cycle. This is so that if a sperm fertilizes an egg, the fertilized egg can implant in the uterine lining. When a fertilized egg does not implant, your body sheds the uterine lining. This is what your period is: the blood, tissue and nutrients that make up the uterine lining leaving your body.

What Happens During Your Period

During your period, the menstrual blood leaves the uterus through the cervix, passes into the vagina, and then leaves the body through the vaginal opening. Periods usually last 3-8 days.

During menstruation, your body is hard at work preparing for a possible pregnancy. Several eggs begin to mature. At around Day 8 of your menstrual cycle (after your period ends), the uterine lining (or endometrium) begins to build again.  After 2-3 weeks, one egg (sometimes two) matures and is released from the ovaries. This is called ovulation. The egg travels down one of the fallopian tubes to the uterus. The egg lives for 12 to 24 hours. Someone is most likely to become pregnant if they have unprotected penis-in-vagina (PIV) sex the day of ovulation or up to 3 days beforehand. This is because the sperm can live in the vagina, uterus and fallopian tubes for 3-5 days. If the egg is not fertilized, it will die and leave the body about 2 weeks later in the menstrual flow (aka period blood).

People with ovaries and a uterus go through the menstrual cycle every month until their ovaries stop producing hormones. This is called menopause, which usually happens around age 50.  The menstrual cycle also stops during pregnancy.

PMS and Cramps

In the week or so before their period starts, some people feel bloated, tired and/or moody.  Some have headaches or get food cravings.  This is known as premenstrual syndrome (PMS). Most people with a uterus have it at some point during their life, but not everyone does. PMS is your body’s reactions to the changing hormone levels in your body. Some people are more sensitive to these changes than others.

It’s common to get cramps during your period. Some people barely notice them, while others have painful cramps. Over the counter painkillers like ibuprofen will help with most cramps. If you have really bad cramps that make you feel sick, doubled over with pain or miss school you may have a medical condition. Talk to your healthcare provider.

Learn more about managing PMS, treating painful period cramps, and what to expect during your period here.

Irregular Periods

It’s common for young people to have irregular periods when menstruation begins.  Your menstrual cycle can be thrown out of whack by rigorous exercise, dieting, stress, medications or for other reasons.  Irregular periods can also be a sign of a hormonal imbalance.  Talk to your doctor if you’re worried about this.

However, if you have had PIV sex and your period doesn’t come or is very light, you might be pregnant.

If you had unprotected sex or a birth control failure and you don’t want to get pregnant, you can use emergency contraception. Emergency contraception stops a pregnancy from beginning. It will not work if you are already pregnant. You can use over the counter Plan B One-Step emergency contraception within 120 hours (5 days) of having sex, or the prescription emergency contraception ella up to 5 days after having sex. The sooner you take it after having intercourse, the more effective it is. Learn more about emergency contraception and how to get it here.

This information is not intended to provide medical advice, professional diagnosis, opinion, treatment or services, only general information for education purposes only.