The ovulation phase is the brief window in your menstrual cycle when a mature egg is released from one of your ovaries. It typically happens once a month, about two weeks before your next period, and it’s the only time during your cycle when pregnancy can occur. The entire event itself lasts just 12 to 24 hours, but the hormonal buildup and fertile window surrounding it span several days.
Where Ovulation Falls in Your Cycle
Your menstrual cycle has four phases: menstruation, the follicular phase, ovulation, and the luteal phase. A normal cycle lasts anywhere from 21 to 35 days, and ovulation sits roughly in the middle. If your cycle is 28 days, you’d typically ovulate around day 14. If your cycle runs longer or shorter, the timing shifts accordingly.
During the follicular phase (the days between your period and ovulation), several follicles in your ovaries begin developing, each containing an immature egg. Usually only one follicle becomes dominant and continues to grow. When that follicle is ready, ovulation is triggered and the egg is released into the fallopian tube, where it can potentially be fertilized by sperm. After ovulation, the luteal phase begins, and the empty follicle transforms into a structure that produces progesterone to prepare the uterine lining for a possible pregnancy.
The Hormonal Chain Reaction Behind Ovulation
Ovulation doesn’t happen randomly. It’s the result of a carefully timed hormonal sequence. During the follicular phase, your ovaries produce rising levels of estrogen as the dominant follicle grows. For most of this time, estrogen actually suppresses the brain’s release of reproductive hormones. But once estrogen reaches a critical threshold, something flips: instead of suppressing, it starts stimulating the brain to release a massive burst of gonadotropin-releasing hormone (GnRH).
This GnRH surge triggers a corresponding spike in luteinizing hormone (LH) from the pituitary gland, known as the LH surge. That LH surge is the direct trigger for ovulation. It causes the dominant follicle to rupture and release its egg. The timing of this surge is partly governed by your body’s internal circadian clock, and progesterone also plays a supporting role by helping activate the brain cells that initiate the cascade. This is why ovulation home tests work by detecting the LH surge in urine: a positive result means ovulation is likely within the next day or two.
How to Recognize Ovulation
Your body gives several signals around ovulation, though not everyone notices them.
Cervical mucus changes. This is one of the most reliable signs. In the days leading up to ovulation, rising estrogen causes your cervical mucus to become wet, slippery, and stretchy, often compared to raw egg whites. This consistency has a biological purpose: thin, wet mucus makes it much easier for sperm to swim through the cervix and into the uterus. After ovulation, mucus typically becomes thicker and less noticeable again.
A slight temperature rise. After ovulation occurs, your basal body temperature (your temperature first thing in the morning, before getting out of bed) increases slightly, typically less than half a degree Fahrenheit (0.3°C). This shift confirms that ovulation has already happened, so it’s more useful for tracking patterns over several months than for predicting ovulation in real time.
Ovulation pain. About one in five women experience a sensation called mittelschmerz, a mild to moderate ache or twinge on one side of the lower abdomen around the time of ovulation. The pain can come from the stretching of the ovary’s surface as the follicle grows, or from fluid or blood released when the follicle ruptures, which can irritate the abdominal lining. It usually lasts a few hours to a day or two.
Some women also notice breast tenderness, mild bloating, or an increased sex drive around ovulation, all driven by the same hormonal shifts.
The Fertile Window
Even though an egg survives only 12 to 24 hours after release, your actual fertile window is longer because sperm can live inside the reproductive tract for three to five days. This means that if you have sex in the days before ovulation, sperm may already be waiting in the fallopian tube when the egg arrives. In practical terms, the fertile window is roughly six days: the five days before ovulation and the day of ovulation itself.
If you’re trying to conceive, the days just before ovulation tend to be the most productive, since the egg-white cervical mucus is at its peak and sperm have time to reach the fallopian tube. If you’re trying to avoid pregnancy, this is the window that matters most, whether you’re using natural family planning methods or simply want to understand your cycle better.
When Ovulation Doesn’t Happen
Sometimes the ovulation phase simply doesn’t occur, a condition called anovulation. You might still have what looks like a period (or irregular bleeding), but no egg is released. This is the most common cause of infertility related to ovulation problems.
Polycystic ovary syndrome (PCOS) is the leading cause, responsible for roughly 70% of anovulation cases. PCOS causes the body to produce too many androgens, which prevent follicles from maturing enough to release an egg. Anovulation is also common at both ends of reproductive life: when periods first start during adolescence and during perimenopause, when the body transitions toward menopause.
Other factors that can disrupt ovulation include having a very low body weight (often linked to eating disorders or excessive exercise), obesity (which can also raise androgen levels), high stress, and primary ovarian insufficiency. All of these interfere with the precise hormonal chain reaction that ovulation requires. Low levels of GnRH, which can result from hypothalamic damage or dysfunction, cut off the cascade at its source by preventing the LH surge from ever happening.
If you suspect you’re not ovulating, tracking your cycle for patterns is a useful first step. Consistently irregular cycles, cycles shorter than 21 days or longer than 35 days, or the absence of the typical signs described above can all point to anovulation. For many causes, addressing the underlying factor, whether that’s managing stress, reaching a healthier weight, or treating PCOS, can restore regular ovulation.