The four phases of the menstrual cycle are menstruation, the follicular phase, ovulation, and the luteal phase. Together they form a repeating loop driven by shifting hormone levels, with a typical cycle lasting anywhere from 21 to 35 days. While 28 days is the textbook average, most people’s cycles fall somewhere within that wider range and still qualify as perfectly normal.
Phase 1: Menstruation
The cycle begins on the first day of your period. Menstruation is triggered by a sharp drop in progesterone, the hormone that had been maintaining the uterine lining during the previous cycle. When the temporary structure in the ovary that produces progesterone (called the corpus luteum) breaks down and hormone levels fall, the thickened lining of the uterus has no hormonal support and begins to shed.
A period typically lasts 2 to 7 days. Normal blood loss is under about 80 milliliters for the entire period, roughly equivalent to five or six tablespoons. Anything consistently heavier than that is considered heavy menstrual bleeding and is often linked to higher levels of inflammatory compounds in the menstrual fluid. During this phase, the uterine lining is at its thinnest, essentially resetting to prepare for the next buildup.
Phase 2: The Follicular Phase
The follicular phase overlaps with menstruation at first, then continues after bleeding stops. It runs from day one of your period until ovulation, making it the most variable phase in length. If your cycle is shorter or longer than average, the follicular phase is usually the reason.
As your period begins, a hormone released by the pituitary gland (FSH, or follicle-stimulating hormone) starts rising. This rise recruits a small group of follicles from a pool of dormant ones in each ovary. Each follicle contains an immature egg. Over the next several days, these follicles grow and begin producing estrogen. Eventually one follicle outpaces the others and becomes the “dominant” follicle, while the rest stop developing and are reabsorbed.
Estrogen levels climb steadily throughout this phase, and you can observe the effects in two measurable ways. First, the uterine lining thickens from nearly nothing to about 12 to 13 millimeters by ovulation, building a fresh, blood-rich environment. Second, cervical mucus changes noticeably. Right after your period, discharge tends to be dry or tacky and white. As estrogen rises through the middle of the follicular phase, it becomes creamy and cloudy. By the days just before ovulation, it stretches between your fingers like raw egg whites and feels slippery, a sign that conditions are most hospitable to sperm.
Phase 3: Ovulation
Ovulation is the shortest phase, lasting roughly 24 hours. It’s the moment when the dominant follicle in one ovary releases a mature egg into the fallopian tube. The trigger is a sudden spike in luteinizing hormone (LH), sometimes called the LH surge. Ovulation occurs on average about 34 hours after the onset of this surge, though the timing varies considerably from person to person, ranging from 22 to 56 hours.
This variability is one reason fertility tracking isn’t always straightforward. At-home ovulation tests detect the LH surge in urine, but the gap between that positive result and actual egg release differs between individuals and even between cycles in the same person. Once the egg is released, it remains viable for about 12 to 24 hours. If it isn’t fertilized in that window, it dissolves.
Your basal body temperature, measured first thing in the morning before getting out of bed, rises slightly after ovulation, typically by less than half a degree Fahrenheit (about 0.3°C). This small but consistent shift confirms that ovulation has already happened, which makes temperature tracking more useful for confirming patterns over multiple cycles than for predicting ovulation in real time. Cervical mucus also shifts quickly after ovulation, drying up and remaining minimal for the rest of the cycle.
Phase 4: The Luteal Phase
After the egg is released, the empty follicle left behind on the ovary transforms into a temporary hormone-producing structure called the corpus luteum. Its primary job is to pump out progesterone, the hormone that prepares the uterine lining to receive a fertilized egg. The luteal phase lasts about 14 days and is remarkably consistent compared to the follicular phase. Most people’s luteal phase stays within a day or two of the same length from cycle to cycle.
Progesterone shifts the uterine lining from a growing phase into a secretory phase. The lining thickens further, reaching about 16 to 18 millimeters, and its glands begin producing nutrients that would support an embryo in the earliest days of implantation. If a fertilized egg does implant, it sends a hormonal signal that keeps the corpus luteum alive and producing progesterone until the placenta can take over, usually around 10 to 12 weeks of pregnancy.
If no pregnancy occurs, the corpus luteum breaks down after about two weeks. Progesterone and estrogen levels plummet, the thickened lining loses its hormonal support, and the cycle resets with menstruation. This is the same progesterone withdrawal that triggers your next period, completing the loop.
How the Phases Connect
The four phases aren’t independent events. They’re linked by a feedback system between the brain and the ovaries. When estrogen is low (during menstruation), the pituitary gland increases FSH to start follicle growth. Rising estrogen from those growing follicles eventually triggers the LH surge that causes ovulation. The corpus luteum then produces progesterone, which suppresses further ovulation. When the corpus luteum dies and progesterone falls, the pituitary ramps up FSH again, and the cycle starts over.
This system can be disrupted in several ways. In polycystic ovary syndrome (PCOS), excess androgen production in the ovaries leads to many small follicles that never mature enough to ovulate, so the cycle stalls before phase three. Thyroid disorders can also interfere by disrupting the signals between the brain and the ovaries. When ovulation doesn’t occur, the luteal phase essentially doesn’t happen either, and periods may become irregular or stop.
Tracking Your Own Cycle
You don’t need lab tests to get a rough sense of which phase you’re in. Three signals are available without any equipment beyond a thermometer: the timing of your period (marking day one), changes in cervical mucus throughout the month, and the small post-ovulation temperature shift. Together, these give you a practical map of your cycle.
Cervical mucus is the most useful real-time indicator. The progression from dry or tacky, to creamy, to stretchy and egg-white-like closely tracks rising estrogen and signals that ovulation is approaching. After ovulation, mucus dries up again and stays that way until the next period. Basal body temperature confirms ovulation after the fact: once you see a sustained rise of about 0.3°C that lasts through the rest of your cycle, you know the luteal phase has begun.
Cycle length alone can also tell you something. Consistently short cycles (under 21 days) or long ones (over 35 days) suggest the follicular phase is either too compressed or too drawn out, which can reflect hormonal imbalances worth investigating. A luteal phase shorter than about 10 days may indicate the corpus luteum isn’t producing enough progesterone, which can affect fertility.