The four phases of the menstrual cycle are menstruation, the follicular phase, ovulation, and the luteal phase. A full cycle typically lasts 24 to 38 days, though the exact length varies from person to person and even month to month. Each phase is driven by shifting levels of hormones that prepare the body for a potential pregnancy, then reset when pregnancy doesn’t occur.
Phase 1: Menstruation
Menstruation is the phase most people recognize: the period itself. It marks day one of the cycle. When no egg has been fertilized in the previous cycle, estrogen and progesterone both drop to their lowest levels. That hormonal withdrawal triggers the top layers of the uterine lining to break down and shed, producing menstrual bleeding that typically lasts three to seven days.
This is the phase where energy tends to bottom out. Cramps in the lower belly or back, headaches, bloating, breast tenderness, and muscle aches are all common. Mood swings and irritability often accompany these physical symptoms, largely because falling hormone levels also reduce serotonin, a brain chemical tied to mood stability. Sleep quality can dip, too. Many people find that the first two days are the most intense, with symptoms easing as bleeding tapers off.
Phase 2: The Follicular Phase
The follicular phase overlaps with menstruation at the start but extends well beyond it, running from day one until ovulation. During this stretch, the pituitary gland releases follicle-stimulating hormone (FSH), which signals the ovaries to start developing several fluid-filled sacs called follicles, each containing an immature egg.
Within a few days, one follicle begins growing faster than the others. This dominant follicle pumps out increasing amounts of estrogen, which does two things at once: it tells the uterus to start rebuilding its lining, and it signals the pituitary gland to dial back FSH production. With less FSH in circulation, the smaller follicles wither away and get reabsorbed by the body, leaving the dominant follicle as the sole contender.
The uterine lining thickens noticeably during this phase. Early on, it measures around 5 to 7 millimeters. By the end of the follicular phase, it reaches roughly 11 millimeters. Rising estrogen also brings a noticeable shift in how you feel. Energy improves, sleep gets better, and many people report increased confidence, motivation, and a generally brighter mood. Cervical mucus transitions from dry or sticky right after your period to creamy and white, then gradually becomes wetter and more slippery as ovulation approaches.
Phase 3: Ovulation
Ovulation is the shortest phase, lasting roughly 24 hours, and it’s the event the entire cycle builds toward. When estrogen from the dominant follicle reaches a critical threshold, it triggers a surge of luteinizing hormone (LH) from the pituitary gland. That LH surge begins about 36 hours before ovulation and lasts around 24 hours. The egg is released from the follicle between 8 and 20 hours after LH peaks.
Once released, the egg is viable for only 12 to 24 hours. This narrow window, combined with the fact that sperm can survive in the reproductive tract for up to five days, is why the fertile window spans roughly six days total: the five days before ovulation plus ovulation day itself.
Your body gives several trackable signals during this phase. Cervical mucus becomes stretchy, slippery, and clear, often compared to raw egg whites. This texture helps sperm travel more easily. Basal body temperature rises slightly after ovulation, typically less than half a degree Fahrenheit (about 0.3°C). Energy and sociability often peak around ovulation, and some people experience mild cramping on one side of the lower abdomen as the egg is released.
Phase 4: The Luteal Phase
After the egg leaves the follicle, the empty sac doesn’t disappear. Instead, it transforms into a temporary structure called the corpus luteum, a yellow-tinged mass of cells that seals itself off and begins producing progesterone. This is the defining hormone of the luteal phase, which lasts roughly two weeks in most cycles.
Progesterone’s primary job is to stabilize and enrich the uterine lining, turning it into an environment that could support an embryo. The lining reaches its maximum thickness during this phase, around 12 to 13 millimeters. Cervical mucus dries up quickly, becoming tacky or nearly absent for the rest of the cycle.
If the egg is fertilized and implants, the body signals the corpus luteum to keep producing progesterone until the placenta can take over. If pregnancy doesn’t happen, the corpus luteum breaks down after about 10 to 14 days. Progesterone and estrogen both plummet, and that drop destabilizes the thickened uterine lining, setting the stage for menstruation to begin again.
The luteal phase is where premenstrual symptoms live. As progesterone rises, you may notice fatigue, bloating, breast tenderness, food cravings, and digestive slowdowns like constipation. When hormone levels drop in the final days before your period, mood swings, anxiety, irritability, trouble sleeping, and headaches become more common. These symptoms vary widely from person to person and cycle to cycle.
How Hormones Drive the Whole Cycle
The cycle runs on a feedback loop between the brain and the ovaries. The pituitary gland releases FSH and LH, and the ovaries respond with estrogen and progesterone. Those ovarian hormones then feed back to the brain, adjusting FSH and LH output up or down. It’s this constant conversation that moves you from one phase to the next.
Estrogen dominates the first half of the cycle, peaking just before ovulation. It drives follicle growth, thickens the uterine lining, and tends to boost energy and mood. Progesterone dominates the second half, maintaining the lining and producing the calmer, sometimes sluggish feeling of the luteal phase. When both hormones drop at the end of the cycle, menstruation begins and the loop starts over.
What Counts as a Normal Cycle
A cycle is considered regular if it falls between 24 and 38 days, measured from the first day of one period to the first day of the next. Cycles shorter than 24 days or longer than 38 days are worth discussing with a healthcare provider. Going 90 days without a period, when you’re not pregnant or breastfeeding, is another signal that something may need attention.
It’s also normal for your cycle length to shift by a few days from month to month. Stress, sleep changes, illness, and weight fluctuations can all nudge the timing. The luteal phase tends to be the most consistent portion, staying close to 14 days, while the follicular phase is where most of the variation happens. A “28-day cycle” is just an average, not a standard everyone should expect to hit.