What Are the Phases of the Menstrual Cycle?

What happens across one menstrual cycle?

A menstrual cycle runs from the first day of one period to the day before the next. Over those weeks, hormones from the brain and the ovaries do two jobs at once: they mature and release an egg, and they build up the lining of the uterus in case that egg is fertilized. If no pregnancy begins, hormone levels fall and the lining is shed. That shedding is your period, and it also marks day 1 of the next cycle.

It can help to think of two cycles running side by side. The ovarian cycle has two halves, follicular and luteal, split by ovulation. The uterine cycle follows along: the lining sheds, rebuilds, then matures. Most guides combine the two into four phases. The table below uses the textbook 28-day cycle, which Cleveland Clinic and the NICHD both use as their reference.

Phase	Typical days (28-day cycle)	Main hormones	What is happening
Menstruation	Days 1 to about 5	Estrogen and progesterone at their lowest	The uterine lining is shed as the period
Follicular	Day 1 until ovulation (about days 1 to 13)	FSH, then rising estrogen	Follicles in the ovary grow; the lining thickens again
Ovulation	Around day 14	A surge of luteinizing hormone (LH)	The ovary releases a mature egg
Luteal	About days 15 to 28	Progesterone rises, then falls if there is no pregnancy	The lining is prepared for a possible pregnancy

The day numbers are a guide, not a rule. Menstruation and the follicular phase also overlap: both start on day 1.

What happens during your period?

The menstrual phase begins on the first day of bleeding. Estrogen and progesterone have dropped at the end of the previous cycle, and that drop signals the uterus to shed its lining, Cleveland Clinic explains. The NHS says a period lasts around 2 to 7 days, and the NICHD puts the average at about 5 days.

What happens in the follicular phase?

The follicular phase also starts on day 1 and lasts until ovulation. Follicle-stimulating hormone (FSH) prompts small fluid-filled sacs in the ovaries, called follicles, to grow. According to the NICHD, estrogen starts to rise once bleeding ends, usually around day 5, and this rise thickens the uterine lining again. Cleveland Clinic notes that, in a typical cycle, one follicle goes on to produce a fully mature egg between days 10 and 14.

This is the phase that stretches or shrinks the most. In the 2019 study by Bull and colleagues, which analyzed 612,613 ovulatory cycles logged by 124,648 users of a fertility app, differences in cycle length came mostly from differences in the follicular phase, that is, from when ovulation happened.

When does ovulation happen?

Ovulation is the moment a mature egg leaves the ovary. It is triggered by a sharp rise in luteinizing hormone. The US Office on Women’s Health (OWH) says LH starts to surge about 36 hours before ovulation and peaks about 12 hours before it, which is why home ovulation tests measure LH in urine.

The NICHD puts ovulation around day 12 to 14 of an average 28-day cycle, but says it can happen anywhere from day 10 to day 21. A more practical way to place it is to count back from the next period: the NHS says ovulation usually happens 10 to 16 days before the next period starts.

Once released, the egg survives for 12 to 24 hours, while sperm can live for several days in the body (OWH says 3 to 5, the NHS says up to 7). That is why the fertile window covers the days leading up to ovulation, not just ovulation day itself.

What happens in the luteal phase?

After ovulation, progesterone rises to prepare the thickened lining for a possible pregnancy, Cleveland Clinic explains. If no pregnancy begins, progesterone and estrogen fall, the lining breaks down, and a new period starts.

The luteal phase is often described as a fixed 14 days. Real data are more varied. Bull and colleagues measured an average luteal phase of 12.4 days, and OWH notes that the time from ovulation to the next period can range from about one week to more than two weeks.

Why don’t real cycles follow the 28-day textbook?

Most bodies do not run on a fixed calendar. In the same 2019 study, the average cycle was 29.3 days, the average follicular phase was 16.9 days, and only 13% of cycles were exactly 28 days long. The researchers also found that the follicular phase became shorter with age, by about 0.19 days a year between ages 25 and 45, while the luteal phase changed very little.

So if your cycle is 32 days, the extra days are most likely in the first half, before ovulation. Your phases are simply placed differently from the textbook diagram. For more on what counts as a typical length, see how long a normal menstrual cycle is.

Can you tell which phase you are in?

Some changes can be noticed day to day. OWH describes a few:

• Cervical mucus becomes clearer and more slippery a few days before ovulation.
• LH tests turn positive during the surge that comes before ovulation.
• Basal body temperature, taken right after waking and before getting up, rises slightly around ovulation.
• One-sided cramping mid-cycle is felt by some people around ovulation; the NICHD calls this mittelschmerz.

The simplest signal is the period itself. Logging the first day of each period for a few months shows how long your cycles really are, and from that you can estimate where each phase usually falls. Lunation does this from the periods you log: it marks your expected period and fertile window, starts from the cycle length you enter until it has your own history, and works without an account.

When is it worth talking to a doctor?

Cycles naturally vary, but some patterns are worth a conversation. ACOG suggests talking to a doctor if you notice:

• cycles shorter than 21 days or longer than 35 days
• cycle lengths that vary by more than 7 to 9 days from one cycle to the next
• bleeding that lasts more than 7 days, or that soaks through a pad or tampon every hour
• bleeding or spotting between periods or after sex
• no period for 3 to 6 months

A doctor or midwife can look at the whole picture, and a few months of tracked dates make that conversation easier.