Understanding your cycle phases: the 4 phases explained simply

Your cycle runs through four phases: menstruation, the follicular phase, ovulation and the luteal phase. In each one your hormones shift, and with them often your energy, your mood and the way your body feels. A cycle lasts 28 days on average, and anything between 21 and 35 days is completely normal. In this article we go through each phase calmly, so you understand your body better.

Contents

• What actually is the menstrual cycle?
• How long does a normal cycle last?
• The four cycle phases at a glance
• Phase 1: Menstruation
• Phase 2: The follicular phase
• Phase 3: Ovulation
• Phase 4: The luteal phase
• Which hormones run the show?
• How do I work out which phase I'm in?
• When are my fertile days?
• What counts as an irregular cycle, and when should you see a doctor?

What actually is the menstrual cycle?

The menstrual cycle is the monthly rhythm in which your body prepares for a possible pregnancy. It starts on the first day of your period and ends the day before the next bleed. During that time an egg matures in your ovary, the lining of your womb builds up, and if no fertilisation happens, that lining is shed again with your period. Then it all begins again.

The whole sequence is run by a finely tuned set of hormones working together. Think of an orchestra: your brain and ovaries send each other signals, and depending on which hormone is setting the tone, you feel different. That is exactly why knowing your own cycle helps so much. It explains why some days you feel ready for anything and on others you would rather pull the duvet over your head.

One thing first: no body runs exactly by the textbook. The numbers in this article are averages. Your own version is allowed to differ, and usually that is perfectly fine.

How long does a normal cycle last?

The famous 28 days are more myth than rule. They are a calculated average, but very few people actually have exactly 28 days month after month. Anything between 21 and 35 days counts as normal. Research even shows that over 80 per cent of cycles vary from month to month. A bit of irregularity is the normal state, not a reason to worry.

Counting always starts on the first day of proper bleeding. Spotting beforehand does not count as day one yet. The last day of your cycle is the day before your next period starts.

One detail is particularly interesting: the second half of the cycle, the time after ovulation, is fairly constant in most people and lasts about two weeks. What makes the cycle longer or shorter overall is almost always the first half, while the egg matures. For some that goes quickly, for others it takes longer. So ovulation shifts from person to person, and from cycle to cycle too.

The four cycle phases at a glance

Before the detail, here is the short version. The cycle can be divided into four phases:

• Menstruation: day 1 to around day 5. The womb lining breaks down and you have your period.
• Follicular phase: day 1 until ovulation. An egg matures, the lining rebuilds, your energy rises.
• Ovulation: roughly mid-cycle. The mature egg is released and you are fertile now.
• Luteal phase: from ovulation to your next period. The body prepares for a possible pregnancy, and many people notice PMS here.

Menstruation and the follicular phase overlap, by the way: your period is the start of the follicular phase. That is why some models talk about three phases and others about four. We stick with four, because for most people the period feels so different from the rest that it makes sense to look at it on its own.

Cycle phase 1: Menstruation

Your period is the starting point of your cycle, even if it often feels more like an ending. Since no pregnancy happened in the previous cycle, the hormones oestrogen and progesterone drop. The upper layer of the womb lining is no longer maintained and comes away. That is your bleed.

A period typically lasts three to seven days. In total you usually lose between 30 and 80 millilitres of blood, even though it often looks like far more. Cramps happen because the muscle of your womb contracts to push the lining out.

Hormonally this is your low point: oestrogen and progesterone are at their lowest. No wonder many people feel more tired, more sensitive or more withdrawn in the first few days. That is not weakness, it is biology. Your body is doing real work right now. Giving it a bit more rest and warmth is not pampering, it matches what is happening inside you.

Cycle phase 2: The follicular phase

The follicular phase begins on the first day of your period and runs until ovulation. It takes its name from the follicles, the small fluid-filled sacs in your ovaries, each holding an egg. At the start of this phase your pituitary gland releases follicle-stimulating hormone, FSH. It makes several follicles start to mature. In the end usually one comes out on top, the dominant follicle.

As the follicles mature, they produce more and more oestrogen. This hormone rebuilds the womb lining you just lost during your period. Oestrogen also has a noticeable effect on how you feel. Many people feel especially alert, clear-headed and sociable in the second half of the follicular phase. Energy comes back, mood lifts, and you often feel up for a lot.

The follicular phase varies the most of all the phases. For some it lasts just over a week, for others two to three weeks. It is the real reason your cycle comes out shorter one month and longer the next. So if your period arrives a little later than expected this month, this is usually where it comes from.

Cycle phase 3: Ovulation

Ovulation is the brief but decisive peak of your cycle. It happens when your oestrogen level reaches its high point and triggers a sudden release of luteinising hormone, LH, in the brain. This LH surge is the signal for the dominant follicle to burst open and release the mature egg. It then travels into the fallopian tube, where it could be fertilised.

In a 28-day cycle ovulation happens around day 14 on average. But as you read above, that is only an average. The better guide: ovulation usually falls about 14 days before your next period, not necessarily 14 days after the last one. With a shorter or longer cycle it shifts accordingly.

The egg itself can only be fertilised for about 12 to 24 hours afterwards. That sounds like a tiny window, and it is. Even so, your fertile window stretches beyond that one day, because sperm can survive in the body for several days. More on that in a moment. Around ovulation many people report a real high: plenty of energy, good mood, more desire for closeness. Some even feel ovulation as a mild pulling on one side of the lower belly, known as mittelschmerz.

Cycle phase 4: The luteal phase

After ovulation the luteal phase begins, running until the first day of your next period. The burst follicle does not simply stay behind, it turns into a small hormone-producing structure, the yellow body. In Latin that is corpus luteum, hence the name of the phase. Its main job is making the hormone progesterone.

Progesterone is the hormone of preparation. It makes your womb lining soft and well supplied with blood, so a fertilised egg could implant. It also raises your body temperature slightly, usually by about 0.3 to 0.5 degrees. That small jump can be measured, and many cycle-tracking methods are built on exactly that.

If no pregnancy happens, the yellow body breaks down after about two weeks. Progesterone and oestrogen fall, and that drop sets off your next period. The days just before bleeding are the hardest of the cycle for many. Irritability, cravings, tender breasts, low mood or feeling thin-skinned: all of that is grouped under the term premenstrual syndrome, PMS for short. It is very common and usually harmless, though it can be unpleasant. If these symptoms weigh on you a lot, it is worth a closer look; you will find further articles at the end.

Which hormones run the show?

Four hormones set the rhythm of the cycle. They mesh together like cogs:

• FSH (follicle-stimulating hormone): comes from the brain and starts the eggs maturing at the beginning of the cycle.
• Oestrogen: made in the maturing follicles, builds up the womb lining and brings energy and good mood in the first half of the cycle.
• LH (luteinising hormone): also comes from the brain and triggers ovulation with a sudden surge.
• Progesterone: made by the yellow body after ovulation, prepares the body for a possible pregnancy and shapes the second half of the cycle.

The nice thing about this system is how well it regulates itself. When one hormone rises, another slows it down or boosts it. When one falls, that is the starting signal for the next step. Once you have grasped this basic pattern, a lot of everyday things suddenly make sense: why your sleep changes, why your appetite swings, why you feel more sociable or more withdrawn on certain days.

How do I work out which cycle phase I'm in?

The simplest place to start is a calendar. Note the first day of every period, ideally over several months. After two or three cycles you get a feel for your own length and can roughly estimate when you ovulate: about two weeks before the next expected bleed.

If you want more precision, watch for physical signs:

• Cervical mucus: around ovulation the mucus at the cervix becomes clearer and stretchier, a bit like raw egg white. After ovulation it turns thicker and cloudier again.
• Basal body temperature: measured right after waking, it rises slightly after ovulation and stays raised through the luteal phase.
• Ovulation tests: they measure the LH surge in urine and so show the fertile days shortly before ovulation.
• How your body feels: energy levels, mood, libido and skin follow a recurring pattern for many people.

An app can help you collect these observations. Just stay realistic: apps that calculate only from the calendar estimate your ovulation, they do not measure it. It gets more reliable once you add your own body signs.

When are my fertile days?

Your fertile window covers about six days: the five days before ovulation plus the day of ovulation itself. The reason for that span is sperm. They can survive up to five days in the female body and wait for the egg. The egg, by contrast, can be fertilised for only about a day. The chance of pregnancy is highest in the one to two days right before ovulation.

That also explains why the calendar method alone is unsafe as contraception. Because ovulation can shift from cycle to cycle, the fertile window cannot be predicted reliably from a calendar. If you want hormone-free contraception, natural family planning methods that combine several body signs are considerably more reliable. Talk to your gynaecologist about which method suits you.

What counts as an irregular cycle, and when should you see a doctor?

A bit of variation is normal, you have read that a few times now. An irregular cycle means the length varies strongly and persistently, or keeps falling outside the 21 to 35 day range. In puberty and around the menopause this is common and usually harmless, because the hormone system is adjusting. Stress, travel, big weight changes, intense exercise or an illness can also throw the cycle off temporarily.

Get your cycle checked by a doctor if you notice any of these:

• your period stops altogether for several months without you being pregnant
• your cycle is persistently shorter than 21 or longer than 35 days
• you have very heavy bleeding or bleeding that lasts longer than seven days
• you have bleeding between periods or after sex
• your period pain is so severe that it limits your daily life

These signs do not automatically mean something serious is going on. But they are worth discussing properly with a doctor. Your cycle is a good gauge of your health, and you are allowed to take it seriously.

This article is general information and does not replace medical advice. If your symptoms are severe, unusual or persistent, please see your gynaecologist.