You may know roughly when your period is due. The cycle also has phase names — follicular, ovulation, luteal — that describe what's happening around it. What happens between one period and the next, and where does ovulation fit?
Your menstrual cycle is a sequence of changes that prepares an egg for release and the lining of your uterus for a possible pregnancy. Hormones coordinate those changes. If pregnancy doesn't happen, hormone levels fall and the lining sheds as your period. That bleeding marks the start of a new cycle.
The phase names come from what happens in the ovaries and the uterus.
Your period is one part of your menstrual cycle
Your period is the bleeding itself. Your cycle includes the days between periods, too: it runs from the first day of one period to the day before the next begins.
For example, if a period starts on September 1 and the next starts on September 30, that was a 29-day cycle. September 30 is day 1 of the new cycle. The number of days you bleed is your period length, which is a different measurement.
Inside your body, two connected processes are taking place. Your ovaries contain eggs, and an egg develops inside a small fluid-filled sac called a follicle. Your uterus, also called your womb, has a lining that changes throughout the cycle. That lining is where a pregnancy can develop.
Hormones are chemical messengers. They help coordinate the development of the egg with changes in the uterine lining, so the two processes happen together.
During your period, the next egg is already developing
At the start of a period, estrogen and progesterone are relatively low. These are two of the main hormones involved in the cycle. The fall in their levels at the end of the previous cycle leads to the shedding of the uterine lining. Blood and tissue leave through the vagina.
Meanwhile, activity in the ovaries is continuing. The pituitary gland, a small gland at the base of your brain, releases follicle-stimulating hormone, usually shortened to FSH. As its name suggests, FSH encourages follicles in the ovaries to grow. Usually, one becomes the leading follicle, with an egg developing inside it.
This part of the ovarian cycle is called the follicular phase. It begins on the first day of your period and continues until ovulation. So you're already in the follicular phase while you're bleeding.
Before ovulation, estrogen helps rebuild the lining
As the leading follicle grows, it produces increasing amounts of estrogen. Estrogen helps the uterine lining grow again after it has shed.
This explains why your body can be preparing for the next part of the cycle even when your period has only recently finished. The developing follicle in the ovary is producing a hormone that changes the lining of the uterus.
When estrogen stays high enough, it helps trigger a surge of another pituitary hormone called luteinizing hormone, or LH. This surge sets ovulation in motion.
Ovulation is the release of an egg
During ovulation, the mature follicle opens and releases its egg. The egg can then enter a fallopian tube, one of the tubes leading toward the uterus.
Ovulation is an event within the cycle. It separates the follicular phase from the luteal phase that follows. Although cycle illustrations often place it on day 14, that isn't a date every body follows.
You may notice that vaginal discharge becomes clearer and stretchier around this time. Some women notice changes more than others. A date on a calendar alone can't establish that an egg has been released.
After ovulation, progesterone supports the lining
The follicle has another job after releasing the egg. The tissue left behind becomes a temporary hormone-producing structure called the corpus luteum. It produces progesterone as well as estrogen.
Progesterone helps the lining become ready to support a possible pregnancy. This part of the cycle is called the luteal phase, named after the corpus luteum. It lasts from after ovulation until the next period begins.
If pregnancy doesn't happen, the corpus luteum breaks down and produces less progesterone and estrogen. As those hormone levels fall, the lining begins to break down and shed. Your next period starts, bringing you back to day 1.
The bleeding you see is therefore connected to changes that have already happened in the ovary.
Why the four phase names can be confusing
You'll often see four labels: menstrual, follicular, ovulation and luteal. They describe useful parts of the process, but they don't divide it into four separate, equal weeks.
The overlap comes from describing different organs. Menstruation describes the uterus shedding its lining. Follicular and luteal describe what's happening in the ovary, with ovulation between them.
That's why menstruation and the early follicular phase happen at the same time. A chart that puts “follicular” only after the period is simplifying the biology.
The order stays the same
This explanation follows a cycle in which ovulation happens. Bleeding can also occur without ovulation, so a bleed by itself doesn't prove that every step took place.
The names make more sense as a sequence: a follicle develops, an egg is released, the tissue left behind supports the lining, and falling hormone levels bring on the next period if pregnancy doesn't happen. Each step follows from the one before it. The dates those steps land on can shift from cycle to cycle — the order they happen in doesn't.