The ovulation cycle is the monthly process your body goes through to prepare and release an egg for potential fertilization. It’s driven by a precise sequence of hormonal shifts that unfold across roughly 28 days, though anywhere from 21 to 35 days is normal for most women. Understanding how this cycle works helps you recognize your fertile window, spot irregularities, and make sense of the physical changes you notice throughout the month.
The Four Phases of the Cycle
Your menstrual cycle has four distinct phases, each with a specific job. They overlap slightly, but thinking of them in sequence makes the whole process easier to follow.
The cycle starts with menstruation, the days you’re actively bleeding as your uterus sheds its lining from the previous cycle. This typically lasts two to seven days. While that’s happening, the next phase is already beginning behind the scenes.
The follicular phase runs from the first day of your period until ovulation. During this time, your brain’s pituitary gland releases a hormone that stimulates your ovaries to develop several small fluid-filled sacs called follicles, each containing an immature egg. Usually one follicle outpaces the rest and becomes the “dominant” follicle. As it grows, it produces rising levels of estrogen, which thickens your uterine lining in preparation for a possible pregnancy. Estrogen levels during this peak climb to 500 to 1,000 percent above where they started at the beginning of the phase.
Ovulation itself happens when that estrogen peak triggers a sudden surge of luteinizing hormone (LH) from the pituitary gland. This surge causes the dominant follicle to rupture and release its mature egg into the fallopian tube. In a 28-day cycle, this usually falls around day 14, but the follicular phase is the most variable part of the cycle, so ovulation can shift earlier or later depending on the month.
The luteal phase follows, lasting roughly from day 15 to day 28. The ruptured follicle transforms into a temporary structure that produces progesterone, which stabilizes the uterine lining and keeps it ready for a fertilized egg to implant. If fertilization doesn’t happen, progesterone drops, the lining breaks down, and your period begins again.
Your Fertile Window
A released egg survives for less than 24 hours. That narrow window is why timing matters so much for conception. However, sperm can survive inside the reproductive tract for up to five days, which means the fertile window actually stretches to about six days total: the five days before ovulation plus the day of ovulation itself.
Because the egg’s lifespan is so short, the most fertile days are generally the two to three days leading up to ovulation, when sperm are already waiting in the fallopian tube. Having sex after ovulation day is far less likely to result in pregnancy because the egg may have already deteriorated.
Physical Signs of Ovulation
Your body gives several signals that ovulation is approaching or has just occurred. Learning to read these can help whether you’re trying to conceive or simply want to understand your cycle better.
Cervical Mucus Changes
The most reliable day-to-day sign is a shift in cervical mucus. In the days after your period, discharge is typically minimal or sticky and thick. As ovulation approaches and estrogen rises, it becomes wetter, more slippery, and stretchy, often compared to raw egg whites. This consistency exists for a reason: thin, wet mucus makes it significantly easier for sperm to swim through the cervix and reach an egg. Once ovulation passes and progesterone takes over, mucus becomes thicker and less abundant again.
Basal Body Temperature
Your resting body temperature shifts slightly after ovulation. The increase is small, typically less than half a degree Fahrenheit (about 0.3°C), but it’s consistent enough to track with a sensitive thermometer each morning before getting out of bed. The catch is that the temperature rise confirms ovulation has already happened, so it’s more useful for confirming a pattern over several months than for predicting the exact day in real time.
Ovulation Pain
About one in five women feel a distinct pain on one side of the lower abdomen around ovulation, sometimes called mittelschmerz. It can range from a brief twinge to a dull ache lasting a few hours. The pain comes from two sources: the growing follicle stretching the surface of the ovary before it bursts, and the small amount of fluid or blood released when the follicle ruptures, which can irritate the abdominal lining. The side where you feel it may alternate from month to month, depending on which ovary releases the egg.
What a Normal Cycle Looks Like
The textbook 28-day cycle gets a lot of attention, but it’s just an average. For most women, cycles between 21 and 35 days are considered normal. Teenagers have an even wider range, from 21 to 45 days, because their hormonal systems are still maturing. Some variation from month to month is expected, too. A cycle that’s 26 days one month and 30 the next doesn’t necessarily signal a problem.
Cycles become irregular when they consistently fall outside those ranges or vary by more than 20 days from one cycle to the next. Between 14 and 25 percent of women experience irregular cycles at some point. Common patterns include cycles shorter than 21 days apart, cycles longer than 35 days apart, or periods that last longer than eight days. An important distinction: irregular cycles can still include ovulation. The timing may just be unpredictable, which makes it harder to identify a fertile window.
When Ovulation Doesn’t Happen
Sometimes the cycle goes through its motions but no egg is released. This is called anovulation, and it’s more common than many people realize.
Polycystic ovary syndrome (PCOS) is the leading cause, responsible for about 70 percent of anovulation cases. In PCOS, the body produces excess androgens (often called “male hormones,” though everyone makes them), which prevent follicles from maturing enough to release an egg. The follicles stay small, and ovulation stalls.
Other causes include thyroid problems (particularly an underactive thyroid), high levels of prolactin from pituitary gland dysfunction, and primary ovarian insufficiency, where the ovaries lose normal function before age 40. Certain medications, including some anti-epileptic and antipsychotic drugs, can also suppress ovulation.
Lifestyle factors play a significant role as well. Body weight at either extreme can interfere with hormonal balance. Obesity increases androgen production, which mimics the hormonal pattern seen in PCOS. Being significantly underweight can cause the brain to reduce the hormonal signals that drive the cycle entirely, leading to missed periods. Chronic stress affects the same brain region (the hypothalamus) that orchestrates those hormonal signals, and sustained stress can delay or block the hormonal cascade needed for ovulation.
Anovulation is also normal at certain life stages. It’s common in the first few years after periods start, when the hormonal system is still calibrating, and again during perimenopause as the ovaries wind down their function.
How the Hormonal Chain Reaction Works
The entire ovulation cycle is coordinated by a feedback loop between three areas of the body: the hypothalamus in the brain, the pituitary gland just below it, and the ovaries. The hypothalamus releases a signaling hormone in pulses, which tells the pituitary to produce the two key hormones that act on the ovaries. One of these hormones stimulates follicle growth early in the cycle. The other, LH, triggers the final rupture of the follicle at ovulation.
What makes the system elegant is the feedback. During the follicular phase, rising estrogen from the growing follicle initially suppresses LH to prevent premature ovulation. But once estrogen crosses a critical threshold, the effect flips: instead of suppressing LH, high estrogen now triggers a massive LH surge. This surge is the final signal that causes the follicle to burst, usually within 24 to 36 hours. The ovaries also produce a peptide that helps fine-tune the timing and size of the LH surge, preventing it from firing too early or too intensely.
After ovulation, progesterone from the leftover follicle suppresses further LH surges, ensuring only one egg is released per cycle in most cases. If no pregnancy occurs, both estrogen and progesterone drop sharply at the end of the luteal phase, the uterine lining can no longer sustain itself, and the cycle resets.