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About the menstrual cycle

The menstrual cycle is a series of changes your body goes through each month to prepare for a possible pregnancy. Each cycle is measured from the first day of your period (day one of your cycle) to the day before your next period.

Your menstrual cycle begins when you have your first period and finishes when you have your final period (menopause).

Learn more about the menstrual cycle, including the different phases of your cycle.

Understanding your menstrual cycle

Changing hormone levels during your menstrual cycle can cause physical and emotional symptoms. It helps to understand your cycle and how it affects you. You can do this by tracking your cycle and writing down any symptoms.

Phases of the menstrual cycle

Watch this video about the menstrual cycle.

The menstrual cycle has four phases.

Your period (menstruation)

Your period is when the uterus lining sheds and flows out of your vagina. Periods contain blood, mucous and cells from the lining of the uterus.

Follicular phase

This phase begins on the first day of your period and lasts for 13 to 14 days. Changing hormone levels cause the uterus lining to thicken and follicles in the ovaries to grow. A follicle is a small sac filled with fluid that can develop into a mature egg.


Ovulation happens when a mature egg is released from an ovary. This usually happens every month, about two weeks before a period.

You are most likely to get pregnant if you have unprotected sex around the time of ovulation.

A few days before ovulation, you might notice that your vaginal mucus is slippery and a similar texture to egg white. You might also feel abdominal pain, often on one side.

If you're trying to get pregnant, you can use an ovulation predictor kit to predict when you are most likely to be fertile.

If you don’t want to get pregnant, it’s important to use contraception throughout your cycle.

Luteal phase

This phase begins after ovulation. It’s when an egg begins to travel to your uterus, and the uterine lining prepares for a pregnancy. If the egg is fertilised by sperm, it attaches to the uterine wall. If pregnancy doesn’t happen, you get your period. Once you get your period, the cycle starts again.

How long is an average menstrual cycle?

Everyone’s menstrual cycle is different, and cycles can change over time. For example, an adolescent’s cycle may last for about 45 days, while people in their 20s and 30s may have a cycle that lasts between 21 and 38 days. The average length of a menstrual cycle is 28 days.

Watch this video about changes that come with puberty, why you get periods and what to expect during your menstrual cycle.

This con­tent has been reviewed by a group of med­ical sub­ject mat­ter experts, in accor­dance with Jean Hailes pol­i­cy.

Reed BG, Carr BR. The Normal Menstrual Cycle and the Control of Ovulation. [Updated 2018 Aug 5]. In: Feingold KR, Anawalt B, Blackman MR, et al., editors. Endotext [Internet]. South Dartmouth (MA):, Inc.; 2000
Last updated: 
21 May 2024
Last reviewed: 
25 March 2024

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