What Is Your Menstrual Cycle Phases Hormones More?

The menstrual cycle is a repeating series of hormonal and physical changes that prepares the body for a possible pregnancy. It has four main phases: menstrual, follicular, ovulation, and luteal. Each phase is driven by shifting levels of hormones including estrogen, progesterone, follicle-stimulating hormone (FSH), and luteinizing hormone (LH). A cycle is counted from the first day of one period to the first day of the next, and for most adults it lasts somewhere between 21 and 35 days.

What Is the Menstrual Cycle and How Does It Work?

The menstrual cycle is the body’s monthly preparation for pregnancy. It is controlled by a feedback loop between the brain and the ovaries.

The hypothalamus, a region at the base of the brain, releases a hormone called GnRH. This signals the pituitary gland to release FSH and LH. Those two hormones act on the ovaries, which respond by producing estrogen and progesterone. The ovaries then send signals back to the brain, and the whole system adjusts based on what it detects.

This loop matters because it explains why cycle problems often trace back to more than just the ovaries. Thyroid conditions, extreme stress, significant weight loss, and intense exercise can all disrupt the brain’s signaling and, in turn, the cycle.

The cycle has two broad halves. The first half (menstrual and follicular phases) is dominated by estrogen. The second half (luteal phase) is dominated by progesterone. Ovulation sits at the transition point between them.

The Four Phases of the Menstrual Cycle Explained

Each phase has a distinct hormonal signature and a distinct job. Understanding them in order makes the whole cycle easier to follow.

Menstrual Phase

This is the bleeding phase. It begins on day 1 of the cycle, which is defined as the first day of full bleeding.

If no pregnancy occurred in the previous cycle, estrogen and progesterone levels drop sharply. That drop causes the lining of the uterus (the endometrium) to break down and shed. This is the period itself.

A typical period lasts about 3 to 7 days. The first day or two often bring the heaviest flow, along with cramping caused by prostaglandins — chemicals that make the uterus contract.

Follicular Phase

The follicular phase overlaps with menstruation and continues until ovulation. It usually runs from day 1 to around day 13 in a 28-day cycle.

During this phase, the pituitary gland releases FSH, which stimulates several follicles in the ovaries to start maturing. Each follicle contains an egg. As they grow, they produce estrogen, and estrogen levels rise steadily through this phase.

Rising estrogen does two important things. It thickens the uterine lining so it can support a pregnancy, and it eventually triggers a surge in LH that leads to ovulation. Usually only one follicle becomes dominant and releases its egg; the others stop developing.

Ovulation

Ovulation is the release of a mature egg from the ovary. It is triggered by a sharp spike in LH, often called the LH surge.

In a 28-day cycle, ovulation typically occurs around day 14. But this timing varies widely between people and even between cycles in the same person. The follicular phase is the part of the cycle that varies most, which is why cycle length differs so much from person to person.

Some people notice a twinge of pain on one side of the lower belly around ovulation. Others notice changes in cervical mucus, which tends to become clearer and more stretchy. These signs are common but not universal, and they are not reliable enough to use alone as proof that ovulation occurred.

The egg lives for roughly 12 to 24 hours after release. Sperm can survive in the reproductive tract for several days. That overlap is why the days just before ovulation are considered the most fertile window.

Luteal Phase

After ovulation, the empty follicle transforms into a structure called the corpus luteum. It produces progesterone, which is the dominant hormone of this phase.

Progesterone prepares the uterine lining for a possible fertilized egg. It also causes a slight rise in basal body temperature, which is why temperature tracking is sometimes used to estimate whether ovulation has happened.

The luteal phase is more consistent in length than the follicular phase. It usually lasts about 14 days, though 12 to 16 days is still within a common range.

If pregnancy does not occur, the corpus luteum breaks down after roughly two weeks. Progesterone and estrogen fall, the uterine lining sheds, and a new cycle begins.

If pregnancy does occur, the developing embryo produces a hormone called hCG, which keeps the corpus luteum alive so it continues making progesterone. This is the same hormone that pregnancy tests detect.

Which Hormones Control the Menstrual Cycle?

Four hormones do most of the work, with two more playing supporting roles. Together they form the feedback loop described earlier.

Two additional hormones matter for context. GnRH from the hypothalamus controls the release of FSH and LH. And a small amount of testosterone is produced by the ovaries and adrenal glands; its role in the cycle is less well understood than the others.

What Does a Normal Menstrual Cycle Look Like?

A typical adult cycle runs 21 to 35 days from the first day of one period to the first day of the next. Cycles outside this range are not automatically a problem, but they are worth discussing with a clinician.

Bleeding usually lasts 3 to 7 days. Flow varies widely between people, and “normal” covers a broad range.

Cycle length and regularity change across a lifetime. In the first few years after menstruation begins, cycles are often long and irregular because the hormonal feedback loop is still maturing. In the years leading up to menopause, cycles often become shorter and more variable before stopping altogether.

Tracking your cycle for a few months can reveal patterns that are hard to notice otherwise. It can also give a clinician useful information if something seems off.

What Causes Irregular Menstrual Cycles?

Irregular cycles are common, and the causes range from harmless to treatable to worth investigating. The most frequent drivers are hormonal shifts, not structural problems.

• Puberty and perimenopause: Irregular cycles are expected during both transitions.
• Stress: High stress can suppress GnRH signaling and disrupt ovulation.
• Weight changes: Significant weight loss or gain can affect hormone production.
• Intense exercise: Very high training loads can interfere with the cycle in some people.
• Thyroid conditions: Both an underactive and an overactive thyroid can affect cycle regularity.
• PCOS (polycystic ovary syndrome): A common hormonal condition associated with irregular ovulation.
• Medications: Some medications, including certain contraceptives, affect bleeding patterns.

If cycles are consistently shorter than 21 days, longer than 35 days, or bleeding is unusually heavy or prolonged, that is a reasonable reason to see a clinician. The same applies to bleeding between periods or after menopause. These patterns can have many causes, and identifying the right one usually requires an exam and sometimes blood tests.

Does Ovulation Always Happen on Day 14?

No. Day 14 is a common estimate for a 28-day cycle, but it is not a rule. Ovulation timing varies between people and between cycles.

The luteal phase is fairly consistent at around 14 days, so cycle length differences mostly come from how long the follicular phase takes. Someone with a 32-day cycle may ovulate closer to day 18. Someone with a 24-day cycle may ovulate closer to day 10.

This matters for anyone trying to conceive or trying to avoid pregnancy. Calendar-based methods assume a fixed ovulation day, and that assumption does not hold for everyone.

It is also possible to have a cycle without ovulating. This is called an anovulatory cycle. It can happen occasionally in anyone and is more common during puberty, in the years before menopause, and in certain hormonal conditions.

What Symptoms Are Common in Each Phase?

Symptoms track with hormone levels, so they tend to follow a predictable pattern for many people. Not everyone notices all of these, and some people notice none.

During the menstrual phase, cramping, fatigue, and lower back discomfort are common. During the follicular phase, many people feel their energy and mood improve as estrogen rises. Around ovulation, some notice mild pelvic pain or changes in cervical mucus. In the luteal phase, bloating, breast tenderness, mood shifts, and food cravings are frequently reported.

When luteal-phase symptoms are strong enough to interfere with daily life, that pattern is often described as PMS (premenstrual syndrome) or, in more severe cases, PMDD (premenstrual dysphoric disorder). PMDD is a recognized condition with specific diagnostic criteria, and it is not simply bad PMS.