The menstrual cycle has four stages: menstruation, the follicular phase, ovulation, and the luteal phase. A full cycle typically lasts 21 to 35 days, with 28 days often used as a reference point. Each stage is driven by shifting hormone levels that prepare the body for a potential pregnancy, then reset if pregnancy doesn’t occur.
Menstruation (Days 1 to 7)
Menstruation is the shedding of the uterine lining. It marks day one of a new cycle. The blood, mucus, and tissue flow out through the vagina over a period that normally lasts 4 to 8 days, with total blood loss ranging from about one-fifth of an ounce to two and a half ounces across the entire period.
Hormone levels are at their lowest point during menstruation. That drop in hormones is what triggered the lining to break down in the first place. But even as bleeding continues, the brain’s pituitary gland is already ramping up production of follicle-stimulating hormone (FSH), which kicks off the next phase.
The Follicular Phase (Days 1 to 14)
The follicular phase overlaps with menstruation because it begins on day one, but it extends well beyond your period, lasting roughly 13 to 14 days. During this time, FSH stimulates several small fluid-filled sacs called follicles to grow on the surface of the ovaries. Each follicle contains an immature egg.
Eventually, one follicle outpaces the others and becomes the “dominant” follicle. This dominant follicle releases increasing amounts of estrogen, which does two things simultaneously. First, it signals the uterine lining to start thickening again, building a fresh, blood-rich layer. Second, the rising estrogen causes the pituitary gland to cut back on FSH. Without enough FSH to sustain them, the remaining follicles wither away and get reabsorbed by the body.
This phase is also where you can see changes in cervical mucus. Early on, discharge tends to be dry or sticky and white. As estrogen climbs through the middle of the phase, it becomes creamier, wetter, and more like yogurt in consistency.
Ovulation (Around Day 14)
Ovulation is the shortest phase, lasting roughly 24 hours. It happens when estrogen levels get high enough to trigger a sudden surge of luteinizing hormone (LH) from the pituitary gland. That LH surge begins about 36 hours before the egg is actually released, and ovulation itself occurs 8 to 20 hours after LH peaks. For most cycles, this falls somewhere around days 13 to 15.
The mature egg bursts out of the dominant follicle and is swept into the fallopian tube, where it begins traveling toward the uterus. The egg survives for only 12 to 24 hours after release. If sperm are present in the fallopian tube during that narrow window, fertilization can occur. If not, the egg disintegrates.
Your body gives a few observable signals around ovulation. Cervical mucus becomes slippery, stretchy, and clear, resembling raw egg whites. This consistency helps sperm travel more easily. Basal body temperature also rises slightly after ovulation, typically by less than half a degree Fahrenheit (0.3°C). That temperature shift confirms ovulation has already happened, which is why temperature tracking works better for identifying patterns over several cycles than for predicting ovulation in real time.
The Luteal Phase (Days 15 to 28)
After ovulation, the now-empty follicle transforms into a temporary structure called the corpus luteum. This structure produces progesterone, the dominant hormone of the luteal phase. Progesterone continues thickening and stabilizing the uterine lining, making it spongy and nutrient-rich so a fertilized egg could implant. Progesterone levels peak about 6 to 8 days after ovulation.
If the egg was fertilized and implants in the uterine lining, the early embryo produces a hormone (hCG, the same one pregnancy tests detect) that tells the corpus luteum to keep making progesterone. This sustains the lining until the placenta develops enough to take over hormone production on its own.
If pregnancy doesn’t occur, no hCG signal arrives. The corpus luteum breaks down, progesterone and estrogen levels drop sharply, and without hormonal support, the thickened uterine lining can no longer maintain itself. It sheds, menstruation begins, and the cycle starts over.
During the luteal phase, cervical mucus dries up noticeably compared to the wet, slippery mucus around ovulation. Many people also notice breast tenderness, bloating, or mood changes in the second half of this phase as progesterone rises and then falls. These premenstrual symptoms are a direct result of that hormonal shift.
Why Cycle Length Varies
The 28-day cycle is a useful model, but most people don’t run on that exact schedule. Healthy cycles can range anywhere from 21 to 35 days. The variation almost always comes from the follicular phase, which can be shorter or longer depending on how quickly a dominant follicle develops. The luteal phase, by contrast, is more consistent, usually lasting around 14 days regardless of total cycle length.
This means that if your cycle is 32 days long, you likely ovulated around day 18, not day 14. If your cycle is 24 days, ovulation probably happened closer to day 10. Understanding this is important if you’re tracking fertility, because the “day 14” rule only applies to cycles that are actually 28 days long.
How Hormones Drive the Entire Cycle
Four hormones orchestrate the cycle in a feedback loop. FSH rises first, prompting follicle growth. As the dominant follicle matures, estrogen climbs and eventually triggers the LH surge that causes ovulation. After the egg is released, progesterone takes over, peaking in the middle of the luteal phase. When no pregnancy occurs, progesterone crashes, the lining sheds, and low hormone levels prompt the pituitary gland to release FSH again.
Each hormone’s rise suppresses or triggers the next one in sequence. Estrogen rising suppresses FSH (so only one egg matures). Estrogen peaking triggers LH (so ovulation happens). Progesterone rising after ovulation suppresses both FSH and LH (so no new follicles develop during the luteal phase). It’s a tightly coordinated chain reaction that repeats every cycle until pregnancy or menopause interrupts it.