Menstrual Cycle Phases Explained

Understand the 4 phases of the menstrual cycle

zoe miller medical editor

Medically reviewed by

Dr Zoe Miller

Last reviewed: 30 Jul 2025

The menstrual cycle is a complex, hormone-driven process that prepares the body for pregnancy. The average cycle lasts between 21 and 35 days, but it can vary from person to person. A combination of hormones controls it, and it consists of 4 main phases: menstrual, follicular, ovulation, and luteal.

Here, we explain what happens during each phase, how hormones change, what symptoms to expect, and when you should seek medical advice.

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The 4 phases of the menstrual cycle

The menstrual cycle is made up of 4 phases:

  1. Menstrual
  2. Follicular
  3. Ovulatory
  4. Luteal

These phases are characterised by fluctuating hormone levels and different physical changes. Understanding what these phases look like can provide a better understanding of your body, including your fertility and overall health.

Your menstrual cycle starts on the first day of your period and ends the day before your next period. The average cycle lasts for 28 days, but this can vary from person to person.

1. Menstrual phase (days 1 to 5)

The menstrual phase is days 1 to 5 of your cycle, during which oestrogen and progesterone levels are at their lowest. It’s the most commonly referred to phase because it’s when your body sheds the womb lining, and a period occurs. The first day of your period is day 1 of your cycle, and your period can last anywhere from 3 to 7 days.

Before your period, oestrogen and progesterone prepare your body for potential pregnancy by thickening the womb lining. When fertilisation does not occur, hormone levels drop and the lining is shed along with blood and mucus, through the vagina, resulting in a period.

Some people also experience other uncomfortable symptoms, including:

  • cramps
  • fatigue
  • feeling sick (nausea)
  • Headaches

2. Follicular phase (days 1 to 13)

The follicular phase is the longest phase of the menstrual cycle, beginning on the first day of your period until ovulation.

At the beginning of the follicular phase, your hormone levels are at their lowest, but oestrogen levels begin to rise around day 6. Your brain also releases gonadotropin-releasing hormone (GnRH) and follicle-stimulating hormone (FSH) to stimulate the production of follicles in your ovaries.

One of these follicles will mature quicker than the rest, this is known as the dominant follicle, and will release an egg during ovulation. At the same time, the dominant follicle releases oestrogen to thicken the womb lining, so that a fertilised egg can implant itself there.

During this phase, you may notice that you:

  • have more energy
  • are sleeping better
  • feel physically strong

Find out more about the best time to exercise on your period in our guide.

3. Ovulation phase (day 14, approximately)

On average, ovulation occurs 14 days before your next cycle begins. A surge in luteinising hormone (LH) triggers ovulation, resulting in a mature egg being released from an ovary.

The egg travels along the fallopian tube to the womb. Some people may get spotting or cramping at this time, while others will not experience any symptoms. You’re likely to notice your sex drive increases at this stage of your cycle. It takes around 24 hours for the egg to make this journey.

Ovulation day and the 3 to 5 days before it are your best time to get pregnant – this is your fertile window. You’ll notice that your vaginal discharge will change at this point, resembling an egg white (clear, stretchy, and slippery). This helps sperm reach the egg, making it easier to conceive. However, if the egg is not fertilised, your body will start its next stage in the menstrual cycle (luteal phase) before starting from the beginning (menstrual) again.

4. Luteal phase (Days 15 to 28)

The luteal phase is the last phase of the menstrual cycle.

After the release of an egg, the follicle changes to a structure called the corpus luteum.

The corpus luteum releases progesterone and causes oestrogen levels to rise, thickening your womb lining in case of pregnancy. Progesterone levels peak during this phase, and if pregnancy occurs, the corpus luteum will continue releasing progesterone to support the growing foetus.

If pregnancy does not occur, the corpus luteum dissolves and your hormone levels fall, signalling to your brain to restart the cycle. During this phase, some women may experience premenstrual symptoms (PMS), including:

  • mood swings
  • feeling depressed or irritable
  • bloating
  • cramping
  • tiredness or difficulty sleeping
  • headaches
  • spots or acne breakouts
  • greasy hair
  • appetite changes
  • breast tenderness
menstrual cycle phases line graph showing how the main 4 hormones rise and fall throughout

Hormones involved in the menstrual cycle

Hormones regulate each stage of the menstrual cycle. The changing levels at each phase cause the physical symptoms you may notice, and prepare your body for potential pregnancy or for your cycle to start again.

The 4 main hormones involved in the menstrual cycle are:

Oestrogen

Produced by the ovaries, oestrogen stimulates the growth of the womb lining, preparing it for pregnancy. It also stops FSH production when levels are high, preventing multiple eggs from maturing in a single cycle.

Progesterone

Progesterone thickens and maintains the womb lining during the luteal phase and during pregnancy. If fertilisation does not happen, progesterone levels fall, triggering a period.

Luteinising hormone (LH)

A surge in LH triggers ovulation or the release of an egg from an ovary.

Follicle-stimulating hormone (FSH)

The pituitary gland produces FSH, which stimulates the ovaries to develop follicles and triggers the release of oestrogen.

How hormonal fluctuations affect your body

The changing hormone levels throughout your menstrual cycle can lead to various physical and emotional changes. For example, oestrogen regulates your mood and mental wellbeing. When they are high, during the follicular phase, you may notice increased energy, better concentration, and a more positive mood.

Progesterone peaks during the luteal phase and is associated with an increased appetite and fluid retention. Progesterone also influences certain neurotransmitters in the brain, promoting sleep and relaxation.

However, just before your period, both oestrogen and progesterone levels drop sharply, which can cause premenstrual syndrome (PMS) symptoms, including irritability, anxiety, and fatigue. In some people, these changes can contribute to more severe symptoms such as premenstrual dysphoric disorder (PMDD).

Tracking the menstrual cycle

Tracking your menstrual cycle offers several benefits, including an enhanced understanding of your body, improved symptom management, and potential insights into your reproductive health. It can also aid in family planning, whether you are trying to conceive or avoid pregnancy.

Some of the key benefits of cycle tracking include:

  • being able to predict when your period will start and understanding your cycle length – especially important if you think you have irregular periods and want to check
  • recognising patterns in your mood, physical symptoms, and appetite changes
  • tracking ovulation to help you avoid or increase your chances of getting pregnant
  • tracking your symptoms to help you manage and understand premenstrual syndrome (PMS) symptoms
  • identifying hormonal imbalances

There are several ways to track your menstrual cycle, including:

  • a calendar or diary
  • period tracking apps
  • ovulation tests
  • cervical mucus monitoring
  • basal body temperature (BBT) monitoring

Common menstrual cycle irregularities

Irregular menstrual cycles are common and may be a symptom of an underlying condition. A regular cycle should be consistent in length, flow, and symptoms. Some common menstrual cycle irregularities include:

  • cycles that are shorter than 21 days or longer than 35 days
  • missed or irregular periods
  • bleeding that lasts longer than 7 days
  • bleeding between periods
  • periods that are accompanied by severe pain, cramping, and feeling sick

What can alter your menstrual cycle?

Several factors can affect your menstrual cycle, such as:

Contraception

Hormonal contraception can alter your menstrual cycle by making your periods shorter, lighter, or less painful if you take the combined pill.

With others, like the contraceptive injection or the mini pill, you may not get a period at all.

Pregnancy

A missed period is one of the earliest signs of pregnancy, and your periods will usually stop while you are pregnant.

Polycystic ovary syndrome (PCOS)

PCOS can significantly impact your menstrual cycle, often causing irregular or absent periods because of infrequent or absent ovulation.

PCOS is one of the most common causes of infertility in people with a womb and is related to abnormal hormone levels, including high insulin and androgen (male hormone) levels.

Eating disorders

More than 50% of people who have periods with an eating disorder experience irregular menstrual cycles. Conditions like anorexia and bulimia can disrupt the hormonal changes that take place during your cycle, which can cause the absence of ovulation or your menstrual cycles may stop altogether.

Uterine fibroids

Uterine fibroids are non-cancerous growths that develop in and around the womb. Many women do not get any symptoms, but 1 in 3 may experience:

  • heavy or painful periods
  • stomach pain
  • constipation
  • needing to pee more often than usual
  • pain or discomfort during sex
  • lower back pain

It’s not fully understood why uterine fibroids develop, but they may be associated with high oestrogen levels because they usually develop during your reproductive years and shrink after menopause.

When to consult a doctor

Often, irregular periods are nothing to worry about, but they can be a sign of an underlying health condition that may require treatment. You should talk to your doctor if:

  • your cycle lasts less than 21 days or more than 35 days
  • your periods last for longer than 7 days
  • you have symptoms like weight gain, tiredness, excessive hair growth, or oily skin
  • you have irregular periods, and you’re struggling to get pregnant
  • you’re bleeding between periods or after sex
  • you have missed 3 periods in a row, and are not pregnant

FAQs

How do I know what phase I am in?

The best way to determine which menstrual phase you are in is to track your period start date and observe any physical symptoms, such as:

  • changes in cervical mucus
  • mood
  • energy levels
  • basal body temperature

If you’re trying to track ovulation, ovulation tests can detect the LH surge that occurs just before an egg is released from your ovaries. Menstrual cycle tracking apps are also a helpful way to track your cycle and predict your current phase according to the information you input.

How long does ovulation last?

Ovulation typically lasts for 12 to 24 hours. This is how long the egg can survive, but your fertile window is longer than this. Sperm can survive for around 5 days in the female reproductive tract.

So, your fertile window includes the 5 days before ovulation, your ovulation day, and sometimes the day after. Understanding when your fertile window is is crucial if you are trying to get pregnant.

What causes irregular periods?

Several factors can cause irregular periods, from lifestyle factors like stress, poor diet, or excessive exercise, to underlying health conditions such as polycystic ovary syndrome, thyroid disorders, and endometriosis. If you are experiencing menstrual irregularities, consult your doctor for a diagnosis and appropriate management or treatment.

How do I know if I have ovulated?

You can find out if you have ovulated by tracking the changes in your body, including cervical mucus, body temperature, and sometimes ovulation pain. Before ovulation happens, your cervical mucus will become thinner, clearer, and more stretchy to help sperm travel towards an egg and fertilise it.

After ovulation, your basal body temperature (BBT) may rise slightly. You will need to track your BBT daily to notice the subtle temperature change. Some people will experience ovulation pain, also known as Mittelschmerz, which is described as a sharp, cramping pain on 1 side of the abdomen.

Ovulation predictor kits can detect the LH surge that triggers ovulation. These can be useful if you’re trying to conceive.

Why is my menstrual cycle getting longer?

A longer menstrual cycle, typically lasting more than 35 days, can be caused by several factors, including hormonal imbalances, stress, weight fluctuations, and excessive exercise. If your cycle is getting longer, contact your doctor for more advice.

Why is my menstrual cycle getting shorter?

A shorter cycle causes your periods to get closer together and can be the result of hormone changes, stress, lifestyle changes, and perimenopause. If your cycle is getting shorter, contact your doctor for further advice.

When is testosterone highest during the menstrual cycle?

Testosterone levels are at their highest around the time of ovulation. They can also rise slightly just before your period begins.

In a normal menstrual cycle, how many eggs are released?

In a normal menstrual cycle, 1 egg is released during ovulation. However, hyperovulation, or the release of more than 1 egg, is relatively common. 40% of people have the potential to release more than 1 egg each month. Non-identical twins are conceived if 2 separate eggs are fertilised and implanted in the womb at the same time.

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