Ovulation is the moment when one of your ovaries releases a mature egg into the fallopian tube, where it can potentially be fertilized by sperm. It happens once per menstrual cycle and is the biological event that makes pregnancy possible. Understanding when and how it occurs is useful whether you’re trying to conceive or trying to avoid it.
How Ovulation Works Inside Your Body
Each ovary contains thousands of tiny structures called follicles, and each follicle holds an immature egg. During the first half of your menstrual cycle (the follicular phase), one follicle begins to grow and mature while the others remain dormant. As this follicle develops, its support cells multiply and fluid fills the space inside it, causing it to swell.
When the egg is fully mature, your brain releases a burst of a hormone called luteinizing hormone, commonly known as LH. This LH surge is the trigger. It causes the wall of the follicle and the surface of the ovary to thin and break open, releasing the egg. The egg, surrounded by a small cluster of protective cells, exits the ovary and enters the fallopian tube. That release is ovulation.
The LH surge begins about 36 hours before ovulation, and it peaks roughly 10 to 12 hours before the egg is released. This is why ovulation predictor kits, which detect LH in urine, can give you advance notice that ovulation is approaching.
When Ovulation Happens in Your Cycle
The average menstrual cycle is about 29 days, but 95% of cycles fall somewhere between 22 and 36 days. Because the first half of the cycle (before ovulation) is the part that varies most, ovulation doesn’t always land on “day 14” the way many people assume.
In a large study of regularly cycling women, only 25% had their entire fertile window fall between days 10 and 17. The full range of fertile days across 95% of cycles spanned from day 4 all the way to day 23. Even the same person can see significant variation from one cycle to the next: more than 42% of women had cycles that varied by more than 7 days over the course of the study. So if your period comes a few days early or late, that’s usually just your ovulation timing shifting, not a sign of a problem.
The Fertile Window
Once released, an egg survives for less than 24 hours. Sperm, on the other hand, can live inside the reproductive tract for up to five days. This means your fertile window is roughly six days long: the five days before ovulation plus the day of ovulation itself. Having sex in the days leading up to ovulation gives sperm time to be already in place when the egg arrives, which is actually more effective than waiting until ovulation day.
Signs Your Body Is About to Ovulate
Your body gives off a few noticeable signals as ovulation approaches. The most reliable one you can observe at home is a change in cervical mucus, the discharge you may notice on your underwear or when wiping.
In the days leading up to ovulation, cervical mucus becomes wet, slippery, and stretchy. The most common description is that it looks and feels like raw egg whites. This texture lasts about three to four days and signals peak fertility. After ovulation, the mucus dries up and becomes thicker or disappears. Tracking this change over a few cycles can help you identify your personal pattern.
Another method is basal body temperature tracking. Your resting body temperature rises slightly after ovulation, typically by 0.4 to 1.0 degrees Fahrenheit (0.2 to 0.6 degrees Celsius). The catch is that this temperature shift confirms ovulation has already happened, so it’s more useful for understanding your cycle over time than for predicting the exact day in a given month. You need to take your temperature first thing in the morning before getting out of bed for the readings to be meaningful.
Some people also notice a brief, sharp pain on one side of the lower abdomen during ovulation, sometimes called “mittelschmerz.” Not everyone feels it, and it’s not a reliable tracking method on its own, but if you do feel it regularly, it can be a helpful secondary clue.
What Happens After the Egg Is Released
If sperm reaches the egg in the fallopian tube and fertilization occurs, the fertilized egg travels down into the uterus and implants in the uterine lining. The empty follicle left behind on the ovary transforms into a structure that produces progesterone, a hormone that supports early pregnancy by keeping the uterine lining thick and stable.
If the egg isn’t fertilized, it dissolves. Progesterone levels drop about two weeks later, the uterine lining sheds, and your period begins. That marks the start of a new cycle, and the process of follicle development begins again.
When Ovulation Doesn’t Happen
Sometimes, a cycle passes without releasing an egg. This is called anovulation. It’s completely normal during certain life stages: when periods first begin in adolescence, during breastfeeding, and in the years leading up to menopause (perimenopause). In these situations, your hormones are naturally fluctuating and cycles may be irregular.
Outside of those life stages, ongoing anovulation can signal an underlying issue. Polycystic ovary syndrome (PCOS) is the most common cause. It involves a hormonal imbalance that prevents follicles from maturing fully, so the egg is never released. Thyroid problems, particularly an underactive thyroid, can also interfere with the hormonal chain of events needed for ovulation.
Lifestyle factors play a significant role too. Very low body weight, eating disorders, and intense long-term exercise can suppress the hormones that trigger ovulation. So can obesity and chronic stress. Certain medications, including some antipsychotics, anti-seizure drugs, and anabolic steroids, can also disrupt the process.
The most common sign that you’re not ovulating is irregular or absent periods. If your cycles are consistently shorter than 21 days, longer than 35 days, or you skip periods frequently outside of the normal life stages mentioned above, it’s worth having your hormone levels checked. Anovulation is one of the most treatable causes of difficulty getting pregnant.