The menstrual cycle has four distinct phases: menstruation, the follicular phase, ovulation, and the luteal phase. A normal cycle lasts between 24 and 38 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.
Menstruation (Days 1 to 5)
Your cycle begins on the first day of your period. During the previous cycle, the lining of your uterus thickened with fluids and nutrients to support a potential pregnancy. When no fertilized egg implants, levels of estrogen and progesterone drop sharply. That hormonal withdrawal triggers the thickened lining to shed, and the tissue exits through your vagina as menstrual fluid.
Most people bleed for three to five days, though anywhere from three to seven days falls within a normal range. Bleeding that regularly lasts longer than eight days is considered heavy menstrual bleeding and worth investigating. During this phase, you may notice cramping as the uterus contracts to help expel its lining.
The Follicular Phase (Days 1 to 13)
The follicular phase overlaps with menstruation, starting on day one and continuing until ovulation. As estrogen and progesterone sit at their lowest point, the pituitary gland (a small structure at the base of the brain) responds by releasing follicle-stimulating hormone. This hormone signals the ovaries to begin growing a batch of 3 to 30 small fluid-filled sacs called follicles, each containing an immature egg.
As these follicles develop, one emerges as the “dominant” follicle and starts producing estrogen. The rising estrogen does two things at once: it suppresses the growth of the other follicles, which gradually break down, and it begins rebuilding the uterine lining that was just shed during your period. The lining thickens progressively throughout this phase, creating a fresh nutrient-rich layer.
The follicular phase is the most variable part of the cycle. In shorter cycles, it may last only 10 days. In longer cycles, it can stretch well beyond 14. This variability is the main reason cycle length differs from person to person and from month to month.
Physical Signs During This Phase
After your period ends, you may notice very little cervical mucus, and the vaginal sensation tends to feel dry. As estrogen climbs in the later part of this phase, mucus gradually appears, first thick, creamy, and whitish, then increasingly wet and stretchy as you approach ovulation. This progression is one of the body’s most visible signals that the fertile window is opening.
Ovulation (Around Day 14)
Ovulation is the shortest phase, lasting roughly 24 hours. It’s triggered by a sudden surge in luteinizing hormone, which the pituitary gland releases in response to the high estrogen output from the dominant follicle. The surge causes the dominant follicle to rupture, releasing a mature egg from the surface of the ovary.
The egg travels into the fallopian tube, where it can be fertilized. Timing is narrow: the egg survives only 12 to 24 hours after release. Sperm, by contrast, can survive in the reproductive tract for up to five days, which is why the fertile window extends several days before ovulation, not just the day it happens. Ovulation typically occurs 24 to 48 hours after the luteinizing hormone surge begins, and more precisely, 8 to 20 hours after the surge peaks.
At ovulation, cervical mucus reaches its most fertile consistency. It becomes transparent, stretchy, and slippery, often compared to raw egg white. Some people also feel a brief, one-sided twinge of pain near the ovary that released the egg.
The Luteal Phase (Days 15 to 28)
Once the egg is released, the ruptured follicle doesn’t disappear. Its cells reorganize into a temporary structure called the corpus luteum, a yellowish mass that functions like a small hormone-producing gland. The corpus luteum’s primary job is to produce progesterone, along with some estrogen.
Progesterone is the dominant hormone of this phase, and it has several effects. It further thickens the uterine lining, filling it with nutrients and blood supply to support a potential embryo. It thickens cervical mucus into a dense plug that blocks sperm and bacteria from entering the uterus. It also raises basal body temperature slightly, typically by 0.4 to 1.0 degrees Fahrenheit, a shift that stays elevated until your next period begins. The combined rise in estrogen and progesterone also causes milk ducts in the breasts to widen, which is why breast tenderness is common in the second half of the cycle.
The luteal phase is more consistent in length than the follicular phase, usually lasting about 14 days. If a fertilized egg implants in the uterine lining, the corpus luteum keeps producing progesterone to sustain the early pregnancy. If implantation doesn’t happen, the corpus luteum breaks down, progesterone and estrogen plummet, and the unsupported lining begins to shed. That shedding is your next period, and the cycle starts again.
Why Cycle Length Varies
While 28 days is often cited as a “textbook” cycle, the actual normal range spans 24 to 38 days. Several factors influence where your cycle falls within that range.
Age is one of the biggest. In the first few years after periods begin, longer and more irregular cycles are common because the hormonal feedback system is still maturing. Cycles tend to shorten and become more predictable through the 20s and 30s, then grow irregular again in the years leading up to menopause. Hormonal birth control, including extended-cycle pills and IUDs, also directly alters cycle patterns.
Beyond age and contraception, several conditions can disrupt regularity. Polycystic ovary syndrome (PCOS) is one of the most common causes of irregular periods. Extreme weight loss, eating disorders, and very high levels of exercise can suppress ovulation entirely. Pelvic inflammatory disease and uterine fibroids can cause irregular or unusually heavy bleeding. Pregnancy and breastfeeding also pause or delay normal cycling. Stress, while harder to quantify, can delay ovulation and lengthen the follicular phase, pushing the whole cycle later.
Tracking Your Cycle With Physical Signs
Two biomarkers let you observe your cycle without any blood tests. Cervical mucus follows a predictable pattern: dry or absent after your period, then gradually thicker and creamier, then wet and egg-white-like around ovulation, then drying up again in the luteal phase. Basal body temperature, your resting temperature taken first thing in the morning, stays lower in the follicular phase and rises after ovulation. The shift is small, less than half a degree Fahrenheit for many people, so tracking it requires a sensitive thermometer and consistent timing.
Neither sign pinpoints ovulation in advance on its own, but together they give a useful picture of where you are in your cycle. Egg-white mucus signals that ovulation is approaching. A sustained temperature rise confirms it already happened.