Ovulation is the moment when one of your ovaries releases a mature egg into the fallopian tube, where it can be fertilized by sperm. It typically happens around day 14 of a 28-day menstrual cycle, though the exact timing depends on your individual cycle length. This single event, lasting only a few minutes, is the centerpiece of the entire menstrual cycle and the only window each month when pregnancy is possible.
How Your Body Prepares for Ovulation
Ovulation doesn’t happen spontaneously. Your body spends roughly two weeks building up to it in what’s called the follicular phase. At the start of each cycle, a hormone called FSH (follicle-stimulating hormone) prompts several small fluid-filled sacs, called follicles, to begin growing on your ovaries. Each follicle contains an immature egg.
These follicles essentially compete with each other. One becomes the “dominant” follicle by growing faster and producing more estrogen, which sends a signal back to the brain to dial down FSH. Without enough FSH, the other follicles stop developing and die off. Only the dominant follicle survives and continues to mature.
As the dominant follicle grows, it pumps out rising levels of estrogen. When estrogen hits a critical threshold, it triggers a sudden, large burst of luteinizing hormone (LH) from the pituitary gland. This is the LH surge, and it’s the direct trigger for ovulation. The LH surge activates enzymes that weaken and thin the wall of the ovary, allowing the mature egg to break through. Within about 24 to 36 hours of the LH surge, the egg is released.
When Ovulation Happens in Your Cycle
A “normal” menstrual cycle is anything between 21 and 35 days. Ovulation generally happens about halfway through, so if your cycle is 28 days, you’d ovulate around day 14. If your cycle runs 32 days, ovulation is closer to day 18. Day 1 is always the first day of your period.
Because cycles vary from month to month, pinpointing the exact day takes some tracking. One common method: look at your shortest and longest cycles over the past six months. Subtract 18 from your shortest cycle and 11 from your longest. Those two numbers give you a range of your most fertile days. For example, if your cycles run between 27 and 32 days, your fertile window falls roughly between days 9 and 21.
The Fertile Window
Once released, an egg survives for less than 24 hours. That’s a narrow window, but the fertile period is actually wider than that because sperm can live inside the reproductive tract for 3 to 5 days. This means you can conceive from sex that happened several days before ovulation, as long as sperm are already waiting in the fallopian tubes when the egg arrives. The highest chance of pregnancy occurs when live sperm are present at the moment of egg release.
In practical terms, the fertile window spans about six days: the five days before ovulation and the day of ovulation itself. The two to three days leading up to ovulation are the most fertile of all.
What Happens After the Egg Is Released
After the egg leaves the follicle, the empty sac doesn’t just disappear. It transforms into a temporary structure called the corpus luteum, a yellowish mass of cells that forms where the follicle once was. The corpus luteum’s main job is producing progesterone, a hormone that thickens the uterine lining to prepare it for a fertilized egg to implant.
If sperm fertilizes the egg and implantation occurs, the early pregnancy produces a hormone called hCG, which keeps the corpus luteum alive and producing progesterone for about 12 weeks. After that, the placenta takes over hormone production and the corpus luteum is no longer needed.
If the egg isn’t fertilized, the corpus luteum breaks down after about 10 to 14 days. Progesterone levels drop, the thickened uterine lining sheds, and your period begins. This starts the cycle over.
Physical Signs of Ovulation
Your body gives several clues that ovulation is approaching or happening. The most reliable one you can observe at home is a change in cervical mucus. In the days leading up to ovulation, discharge becomes wet, stretchy, and slippery, closely resembling raw egg whites. You can check the texture by stretching it between two fingers. This egg-white mucus typically lasts about three to four days and signals your most fertile time.
Other signs some people notice include mild one-sided pelvic pain (sometimes called mittelschmerz), breast tenderness, a slight increase in sex drive, or light spotting. After ovulation, basal body temperature rises slightly, though this shift confirms ovulation already happened rather than predicting it in advance.
Tracking Ovulation With Test Kits
Over-the-counter ovulation predictor kits (OPKs) work by detecting the LH surge in your urine. When the test reads positive, ovulation is likely about 24 to 36 hours away. These kits are quite accurate. A 2024 study comparing five popular brands found that surge detection accuracy ranged from about 92% to 97% when compared against blood tests for LH. Brands like Pregmate and Easy@Home performed slightly better on sensitivity (around 75 to 77%) than some competitors, but all five showed similar reliability for negative and positive predictive value.
For best results, test in the early afternoon rather than first thing in the morning, since LH is typically synthesized overnight and appears in urine later in the day. Start testing a few days before you expect to ovulate based on your cycle length.
When Ovulation Doesn’t Happen
Sometimes the body skips ovulation entirely in a given cycle, a condition called anovulation. Occasional missed ovulation is normal, especially if you’ve recently started menstruating or are approaching menopause. But chronic anovulation is the most common cause of infertility and deserves attention.
Polycystic ovary syndrome (PCOS) is responsible for about 70% of anovulation cases. In PCOS, the body produces too many androgens (often called “male hormones,” though everyone makes them), which prevent follicles from maturing enough to release an egg. They stay small instead of going through the growth process that leads to ovulation.
Other factors that can disrupt ovulation include obesity (which also increases androgen production), having a very low body weight or BMI from restrictive eating or excessive exercise, thyroid disorders, high stress levels, and pituitary gland problems that reduce LH and FSH output. Even the hypothalamus, the brain region that kicks off the whole hormonal chain, can malfunction under chronic stress or extreme calorie restriction, cutting off the signal that starts the process.
Treatment depends on the underlying cause. For some people, reaching a healthier weight in either direction restores regular ovulation. Stress management through techniques like meditation or yoga can help when stress is the primary driver. When lifestyle changes aren’t enough, medications that stimulate follicle growth or trigger the LH surge can be used to induce ovulation.