The menstrual cycle has four distinct phases: menstruation, the follicular phase, ovulation, and the luteal phase. A full cycle averages 28 days but anywhere from 21 to 35 days is considered normal. Each phase is driven by shifting hormone levels that prepare the body for a potential pregnancy, then reset if one doesn’t occur.
Phase 1: Menstruation (Days 1 to 5)
The cycle begins on the first day of your period. When no fertilized egg has implanted in the uterine lining, levels of both estrogen and progesterone drop sharply. That hormonal withdrawal signals the uterus to shed its lining, which exits the body as menstrual fluid. A typical period lasts 3 to 7 days.
Total blood loss during a normal period is about 60 milliliters, or roughly 2.7 ounces. Regularly losing more than 80 milliliters per cycle is classified as heavy menstrual bleeding and worth discussing with a healthcare provider. Cervical mucus during and immediately after your period tends to be minimal, dry, or slightly tacky.
Phase 2: The Follicular Phase (Days 1 to 13)
The follicular phase actually overlaps with menstruation, starting on day 1 and lasting until ovulation. During this stretch, the pituitary gland (a small structure at the base of the brain that controls hormone production) releases follicle-stimulating hormone, or FSH. FSH activates the ovaries to begin developing fluid-filled sacs called follicles, each containing an immature egg.
Over the next several days, one follicle outpaces the others and becomes the “dominant” follicle. As it matures, it releases increasing amounts of estrogen into the bloodstream. That rising estrogen does two important things. First, it thickens the uterine lining so a fertilized egg could implant there. By the time ovulation arrives, the lining typically measures 12 to 13 millimeters. Second, the estrogen spike signals the pituitary gland to dial back FSH production. Without enough FSH, the remaining smaller follicles wither away, leaving only the dominant one.
You can observe this phase through cervical mucus changes. In the early follicular phase, mucus is sticky and white. As estrogen climbs toward its peak around days 10 to 14, mucus becomes wetter, stretchier, and slippery, often compared to raw egg whites. That egg-white consistency is the body’s way of creating a sperm-friendly environment right before ovulation.
Phase 3: Ovulation (Around Day 14)
Ovulation is the shortest phase, lasting roughly 24 hours. It’s triggered when the rising estrogen from the dominant follicle reaches a threshold that causes a sudden surge of luteinizing hormone (LH) from the pituitary gland. About 36 to 40 hours after the LH surge begins, the mature follicle ruptures and releases its egg into the fallopian tube.
The released egg survives for only 12 to 24 hours. However, sperm can live in the reproductive tract for up to 5 days, which is why the total fertile window stretches to about 6 days per cycle: the 5 days before ovulation plus the day of ovulation itself. If you’re tracking fertility, this is the window that matters most.
Your basal body temperature (your temperature first thing in the morning, before getting out of bed) rises slightly after ovulation, typically by less than half a degree Fahrenheit. That small shift confirms ovulation has already happened, which is why temperature tracking works better for confirming patterns over several cycles than for predicting ovulation in real time.
Phase 4: The Luteal Phase (Days 15 to 28)
After the egg is released, the empty follicle left behind in the ovary transforms into a temporary hormone-producing structure called the corpus luteum. Its cells enlarge and accumulate a yellow pigment called lutein (the name “luteal” comes from this coloring). The corpus luteum’s primary job is to pump out progesterone.
Progesterone takes over from estrogen as the dominant hormone. It shifts the uterine lining from a growth phase into a maintenance and preparation phase, making it spongy, nutrient-rich, and ready to support an embryo. During this secretory stage, the lining reaches its maximum thickness of about 16 to 18 millimeters. Progesterone also counteracts the effects of estrogen on the lining, essentially stabilizing it rather than letting it keep growing.
If fertilization occurs, the developing embryo sends a hormonal signal that keeps the corpus luteum alive and producing progesterone. If fertilization doesn’t happen, the corpus luteum breaks down after about 10 to 14 days. Progesterone and estrogen levels plummet, the thickened lining can no longer sustain itself, and menstruation begins. The cycle resets.
Cervical mucus during the luteal phase dries up considerably compared to the fertile window. Many people notice very little discharge in the days leading up to their period.
How the Phases Feel Day to Day
The hormonal shifts across these four phases often produce noticeable physical and emotional changes. During the follicular phase, as estrogen steadily climbs, many people report higher energy, improved mood, and clearer skin. The days around ovulation tend to feel like a peak: higher libido, more sociability, and that characteristic stretchy cervical mucus.
The luteal phase is where premenstrual symptoms show up. Progesterone can cause bloating, breast tenderness, fatigue, and mood changes. These symptoms tend to intensify in the final days before menstruation as both progesterone and estrogen drop. The severity varies widely from person to person and even cycle to cycle.
Why Cycles Vary in Length
When cycle length varies, it’s almost always because the follicular phase changed. Some months, the dominant follicle matures quickly; other months, it takes longer. Stress, illness, significant weight changes, and intense exercise can all delay follicle development and push ovulation later, which lengthens the overall cycle.
The luteal phase, by contrast, is relatively consistent. It almost always lasts between 10 and 14 days regardless of total cycle length, because the corpus luteum has a fixed lifespan. So if your cycle runs 35 days instead of 28, ovulation likely happened around day 21 rather than day 14, while the luteal phase still lasted its usual duration.