The four phases of the menstrual cycle, in plain words

By the Twilune team, checked against the sources below · October 27, 2026 · 7 min read

The menstrual cycle has four phases: menstrual, follicular, ovulatory and luteal. Each one is a stretch of time with its own mix of hormone changes, and the cycle is counted from the first day of one period to the first day of the next. The lengths below are typical, not a rule for your body.

What are the four phases of the menstrual cycle?

Doctors usually describe the cycle in four parts. In order, they are the menstrual phase, the follicular phase, ovulation and the luteal phase. Two hormones, estrogen and progesterone, drive much of the pattern, with help from two signals sent by the brain: follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

A quick map before the detail:

Notice that the follicular phase starts on the same day as the menstrual phase. That is how Cleveland Clinic and others describe it, so the two overlap. Some charts show only the part after your period ends. Both are fine, as long as you know which one you are looking at.

What happens in the menstrual phase?

This is your period. If there was no pregnancy, estrogen and progesterone drop to very low levels, and that fall tells the body to shed the lining of the uterus. Most people bleed for three to five days, and the NHS says anywhere from two to seven days is within the usual range.

The most common symptom in this phase is cramping, which comes from the uterus contracting to release its lining. Cleveland Clinic also lists general period symptoms that are not tied to one phase: mood changes, trouble sleeping, headache, food cravings, bloating, breast tenderness and acne. Not everyone gets all of them, and the mix often changes from cycle to cycle.

If your pain is severe or your bleeding is very heavy, that is worth a doctor's visit. More on that at the end.

What happens in the follicular phase?

While your period is still going, the brain releases FSH. It makes follicles in the ovaries grow, and each follicle holds an egg. Estrogen rises as the follicles develop, and it thickens the uterine lining again. Around days 10 to 14 in a 28-day cycle, one follicle matures into the egg that will be released.

This is the most variable phase. In a study of more than 600,000 cycles from cycle-tracking app users, the follicular phase averaged about 17 days but ranged widely, and the authors found that most of the difference in cycle length between people came from this phase. In plain terms: a longer cycle usually means ovulation came later, not that everything else was stretched.

What happens during ovulation?

Ovulation itself is one event: a sudden rise in LH triggers the ovary to release an egg. Twilune and its calculator call the few days around it the ovulatory phase, or inner summer.

You may have heard that ovulation happens on day 14. That is true only in a textbook cycle. In the large study above, even in cycles that were exactly 28 days long, the average follicular phase was 15.4 days, so ovulation did not land on day 14 on average. Only 13 percent of all cycles in the study were 28 days long. The authors say plainly that the belief that ovulation consistently occurs on day 14 is not correct.

That matters for any app or chart that tells you what day you are "supposed" to be in a phase. Counting days gives an estimate, not a measurement. We come back to this in why period predictions are ranges.

What happens in the luteal phase?

After the egg is released, the follicle becomes a small structure that makes progesterone and some estrogen. Progesterone rises and prepares the lining of the uterus. If there is no pregnancy, that structure breaks down, hormone levels fall, and the lining is shed. That fall is the start of your next period.

Cleveland Clinic says the luteal phase averages 12 to 14 days, and that 10 to 17 days is considered normal. It is more consistent from cycle to cycle than the follicular phase: in the large study, the luteal phase averaged 12.4 days and varied less than half as much.

This is also the phase where many people notice premenstrual symptoms. The Office on Women's Health describes premenstrual syndrome (PMS) as a mix of physical and emotional symptoms that many people have after ovulation and before their period. Over 90 percent report at least some premenstrual symptoms, and for most they are mild. If the week before your period is hard, we wrote about it in luteal phase mood.

Do you feel different in each phase?

Some people do, and some do not. This is where charts often promise more than the research shows.

The strongest evidence is for the luteal phase and PMS, because symptoms in the days before a period are well documented. For the other phases the picture is thinner. A 2025 meta-analysis of 102 studies, covering almost 4,000 participants, found no robust evidence that thinking skills such as attention, memory or verbal ability shift across the cycle. The authors note that the studies were often small and used loose definitions of phase, so this does not prove that nobody is affected. It does mean that a claim like "you are sharper in this phase" is not supported for people in general.

What is true for many people is that they notice their own pattern: more energy at some point, more tiredness at another, a few low days before bleeding starts. Those are worth noticing. They are just not the same for everyone, and a calendar of phases cannot tell you what yours will be.

What are inner winter, spring, summer and autumn?

In Twilune we call the four phases inner winter (menstrual), inner spring (follicular), inner summer (ovulatory) and inner autumn (luteal). It is a framing, not science. The seasons give you a gentle way to think about a cycle, a period of rest, a rise, a peak and a wind-down, and some people find that easier to remember than medical terms.

The weather metaphor is a mood board, not a forecast. Your inner summer might feel flat, and your inner winter might be your most productive week. If your own logs say so, trust them over the metaphor.

Planning workouts or food around these phases is popular. Before you do, read what the evidence says about cycle syncing.

How do you know which phase you are in?

Counting from the first day of your period gives you a rough guess. If you know your usual cycle length and when your last period started, you can estimate where you are now. The free cycle phase calculator does exactly that. It is an estimate based on averages, and it works best for regular cycles.

For a better guess over time, you need your own history. Logging your period start dates for a few cycles shows how long your cycles really are and how much they vary. That is the idea behind a good tracker: use your own data, not a 28-day template.

Twilune does this on your phone. It predicts your next period and your cycle phases from your own history, and shows a range with a confidence level instead of a single day. It is not a medical device and not medical advice.

When should you see a doctor about your cycle?

Phases are a way to understand a normal pattern. They are not a way to rule out a problem. See a doctor if:

• Your period pain is severe, or it stops you doing what you usually do.
• Your bleeding is very heavy. The NHS lists signs such as changing a pad or tampon every one to two hours, passing clots bigger than a 10p coin, or bleeding that lasts more than seven days.
• You bleed between periods or after sex.
• You have missed periods without a clear reason, such as pregnancy. The NHS suggests seeing a GP after three missed periods in a row if you have had sex and a pregnancy test is negative.
• Your mood in the days before a period makes life hard. If you ever have thoughts of harming yourself, contact your local emergency number or a crisis line straight away.

Twilune is not a medical device, and nothing here is medical advice. A doctor can look at your whole picture.

Frequently asked questions

This article is general information, not medical advice. If something worries you, or your symptoms are severe or getting in the way of your life, talk to a doctor. If you are thinking about harming yourself, call your local emergency number now.