The menstrual cycle has four distinct phases: the menstrual phase, the follicular phase, the ovulatory phase, and the luteal phase. A full cycle typically lasts 21 to 35 days, counted from the first day of one period to the first day of the next. Each phase is driven by shifting hormone levels that prepare the body for a potential pregnancy, then reset when pregnancy doesn’t occur.
The Menstrual Phase (Days 1 to 7)
Your cycle begins on the first day of bleeding. At the end of the previous cycle, levels of the hormone progesterone drop sharply, and that drop signals the uterine lining to break down and shed. This is your period. Bleeding typically lasts 2 to 7 days, with most people finishing by day 7.
This phase often comes with the most noticeable physical symptoms: cramping in the lower belly or back, bloating, breast tenderness, headaches, muscle aches, and low energy. Sleep quality tends to dip. Emotionally, mood swings and irritability are common. These symptoms generally ease as bleeding tapers off.
The Follicular Phase (Days 1 to 13)
The follicular phase overlaps with menstruation, starting on day 1 and lasting until ovulation. During this stretch, the pituitary gland (a small gland at the base of the brain) releases follicle-stimulating hormone, or FSH. FSH tells the ovaries to start developing follicles, which are small fluid-filled sacs that each contain an immature egg. Several follicles begin growing, but usually only one becomes dominant.
That dominant follicle produces increasing amounts of estrogen. Rising estrogen does two important things. First, it thickens the uterine lining so a fertilized egg could implant there. The lining grows to about 12 to 13 millimeters, roughly half an inch, by the end of this phase. Second, the estrogen spike signals the pituitary gland to slow down FSH production, which prevents additional follicles from maturing.
Most people feel noticeably better during the follicular phase compared to menstruation. Energy and sleep quality improve, bloating fades, and many people report feeling more motivated, confident, or generally upbeat as estrogen climbs.
The Ovulatory Phase (Around Day 14)
Ovulation is the shortest phase, lasting only about 24 hours. It’s triggered by a sudden surge in luteinizing hormone (LH), which spikes roughly 24 to 48 hours before the egg is released. That LH surge causes the dominant follicle to rupture and release a mature egg into the fallopian tube.
Once released, the egg survives for only 12 to 24 hours. Sperm, however, can live inside the reproductive tract for 3 to 5 days. That means the fertile window extends from about five days before ovulation through the day of ovulation itself, giving a roughly six-day window where pregnancy is possible.
Physically, you may notice mild cramping on one side of the lower abdomen (sometimes called mittelschmerz), a slight rise in basal body temperature, and changes in vaginal discharge, which often becomes clearer and more slippery. Energy tends to stay high, and many people feel more social and confident around ovulation. Basal body temperature rises by 0.4 to 1 degree Fahrenheit after ovulation occurs, which is why temperature tracking can help confirm that you’ve ovulated, though it can’t predict it in advance.
The Luteal Phase (Days 15 to 28)
After the egg is released, the empty follicle transforms into a temporary structure called the corpus luteum. Its primary job is to pump out progesterone, the hormone that further prepares the uterine lining for a potential pregnancy. The lining thickens to 16 to 18 millimeters during this phase.
If the egg isn’t fertilized, the corpus luteum starts to break down around 10 days after ovulation. As it disintegrates, progesterone levels fall. Without progesterone to sustain it, the thickened uterine lining can no longer maintain itself, and the cycle resets with menstruation. The luteal phase lasts about 14 days and is the most consistent part of the cycle. When cycle length varies from person to person, it’s usually because the follicular phase is shorter or longer, not the luteal phase.
This is the phase most associated with premenstrual symptoms. Breast tenderness, bloating, food cravings, headaches, constipation, and trouble sleeping are all common as progesterone rises and then drops. Emotionally, the late luteal phase can bring mood swings, irritability, sadness, anxiety, and fatigue. These symptoms tend to peak in the final days before your period starts.
How Hormones Drive the Whole Cycle
The four phases are really a chain reaction between four hormones: FSH, estrogen, LH, and progesterone. FSH kicks off follicle growth. Rising estrogen from the growing follicle thickens the uterine lining and eventually triggers the LH surge. The LH surge causes ovulation. The leftover follicle then produces progesterone, which maintains the lining. When progesterone drops, the lining sheds, and the cycle starts over.
This feedback loop is why factors like stress, significant weight changes, or hormonal conditions can shift your cycle length or cause missed periods. The hormones involved are sensitive to signals from other body systems, so no two cycles are guaranteed to be identical. Cycles that consistently fall between 21 and 35 days are considered within the normal range, even if they don’t land on a textbook 28 days every time.