A woman’s menstrual cycle has four phases: menstruation, the follicular phase, ovulation, and the luteal phase. A full cycle typically lasts 21 to 35 days, with 28 days as the average. Each phase is driven by shifting hormones that prepare the body for a potential pregnancy, then reset if pregnancy doesn’t occur.
Menstruation (Days 1 to 7)
Menstruation is the phase most people think of first. It marks day one of a new cycle. When no pregnancy has occurred, the thickened lining of the uterus has no purpose, so it sheds and flows out through the vagina. Most people bleed for three to five days, though anywhere from two to seven days falls within a normal range.
During this phase, both estrogen and progesterone are at their lowest levels. That hormonal drop is what triggers the shedding in the first place. Many people experience cramping, fatigue, or bloating in the first couple of days as the uterus contracts to expel its lining. Cervical mucus is typically minimal, thick, or dry during this time.
The Follicular Phase (Days 1 to 13)
The follicular phase overlaps with menstruation, starting on day one and running until ovulation. While bleeding is still happening, the brain’s pituitary gland begins releasing a hormone called FSH (follicle-stimulating hormone). FSH signals the ovaries to start developing small fluid-filled sacs called follicles, each containing an immature egg.
Several follicles begin growing, but usually only one becomes dominant. That dominant follicle produces increasing amounts of estrogen as it matures. The rising estrogen does two things: it thickens the uterine lining to prepare for a possible embryo, and it signals the pituitary gland to slow down FSH production so the other follicles stop developing. By around days 10 to 14, the dominant follicle contains a fully mature egg.
You may notice changes in how you feel during the second half of this phase. As estrogen climbs, many people report higher energy, improved mood, and clearer skin. Cervical mucus gradually shifts from thick and white to wetter and more slippery as ovulation approaches.
Ovulation (Around Day 14)
Ovulation is the shortest phase, lasting roughly 12 to 24 hours. It happens when the mature egg is released from the ovary and enters the fallopian tube. In a 28-day cycle, this occurs around day 14, though the exact timing varies from person to person and even cycle to cycle.
The trigger is a sharp spike in luteinizing hormone (LH). This LH surge typically happens about 24 hours before the egg is released, though it can occur anywhere from 16 to 48 hours beforehand. This is the window that ovulation predictor kits detect.
Ovulation is the most fertile point in the cycle. The egg survives for about 24 hours after release, and sperm can live in the reproductive tract for up to five days, so the fertile window extends to roughly six days total. Cervical mucus at this stage becomes clear, slippery, and stretchy, often compared to raw egg whites. This consistency helps sperm travel toward the egg.
Tracking Ovulation
Two of the simplest ways to identify when ovulation has occurred are monitoring cervical mucus and tracking basal body temperature. Your resting body temperature rises slightly after ovulation, typically by less than half a degree Fahrenheit (0.4°F to 1°F). The catch is that the temperature shift confirms ovulation after the fact rather than predicting it in advance. Combining temperature tracking with cervical mucus observations gives a more complete picture over several cycles.
The Luteal Phase (Days 15 to 28)
After the egg is released, the empty follicle left behind on the ovary transforms into a temporary structure called the corpus luteum. Its primary job is producing progesterone, the hormone that maintains and further thickens the uterine lining so it can support a fertilized egg.
The corpus luteum also produces some estrogen, but progesterone is the dominant hormone of this phase. Progesterone changes the uterine environment in specific ways: it increases blood supply to the lining, triggers the release of nutrients, and generally prepares the uterus as a place where an embryo could implant and grow.
If the egg is fertilized and implants, the body begins producing a pregnancy hormone that keeps the corpus luteum alive. If fertilization doesn’t happen, the corpus luteum breaks down after about 10 to 14 days. Progesterone and estrogen levels drop sharply, and without hormonal support, the uterine lining begins to shed. That brings you back to day one: menstruation.
The luteal phase is when many people experience premenstrual symptoms. Rising progesterone can cause bloating, breast tenderness, mood changes, food cravings, and fatigue. Cervical mucus returns to being thick and dry shortly after ovulation and stays that way through the rest of the phase.
What Counts as a Normal Cycle
Cycles between 21 and 35 days are considered normal. Some variation from month to month is expected, but if the gap between your shortest and longest cycles regularly exceeds nine days, that level of inconsistency is worth paying attention to. For example, alternating between 25-day and 34-day cycles suggests your hormonal signals may not be following a consistent pattern.
A few specific patterns fall outside the normal range:
- Cycles shorter than 21 days or longer than 35 days
- Periods lasting longer than seven days
- Missing three or more periods in a row (when not pregnant, breastfeeding, or in menopause)
- Bleeding that soaks through a pad or tampon in an hour
- Spotting between periods or after sex
- Severe pain, nausea, or vomiting with periods
No period by age 15 or 16, or within three years of breast development, is also considered outside the typical range. The absence of a period for 90 consecutive days is classified as abnormal unless pregnancy, breastfeeding, or menopause (which generally occurs between ages 45 and 55) explains it.
How Hormones Drive the Whole Cycle
The four phases feel distinct, but they’re really one continuous feedback loop between the brain and the ovaries. FSH kicks off follicle growth. Rising estrogen from those follicles thickens the uterine lining and eventually triggers the LH surge. The LH surge causes ovulation. The leftover follicle becomes the corpus luteum and pumps out progesterone. If no pregnancy occurs, progesterone drops, the lining sheds, and low hormone levels signal the brain to start releasing FSH again.
When this loop runs smoothly, cycles are predictable and symptoms are manageable. When one part of the chain underperforms, such as the corpus luteum not producing enough progesterone, the lining may not develop properly, leading to irregular or unusually light periods. Understanding which phase you’re in at any given time can help you make sense of physical symptoms, plan or prevent pregnancy, and recognize when something has shifted in your cycle.