When you ovulate, one of your ovaries releases a mature egg into a fallopian tube, where it can be fertilized by sperm. This typically happens about 12 to 14 days before the start of your next period. The process involves a precise chain of hormonal signals, physical changes you can sometimes feel, and a narrow window of fertility that lasts only a few days each cycle.
The Hormonal Chain Reaction
Ovulation doesn’t happen all at once. It’s the result of a weeks-long buildup of hormonal signals between your brain and ovaries. Early in your cycle, your pituitary gland (a small gland at the base of your brain) releases a hormone called FSH, which tells several follicles in your ovaries to start growing. Each follicle contains an immature egg. Usually one follicle becomes dominant, outpacing the others, and its growing egg produces rising levels of estrogen.
When estrogen reaches a critical threshold, usually around day 13 of a 28-day cycle, it triggers a sudden surge of another hormone called LH. This LH surge is the final signal. It sets off a cascade of changes inside the dominant follicle: the egg completes its final stage of maturation, the follicle wall weakens, and eventually the egg breaks free. Ovulation occurs 28 to 36 hours after the LH surge begins, and about 10 to 12 hours after LH hits its peak. This is what ovulation prediction kits detect: that LH spike in your urine.
What Physically Happens Inside Your Body
In the hours leading up to ovulation, the dominant follicle swells to about 2 centimeters across, stretching the surface of the ovary. When the follicle finally ruptures, the egg is swept into the nearest fallopian tube by tiny finger-like projections called fimbriae. A small amount of fluid and sometimes a trace of blood escapes from the ruptured follicle at the same time, which can briefly irritate the lining of your abdomen.
Once the egg is gone, the empty follicle doesn’t just disappear. It transforms into a temporary structure called the corpus luteum, a saffron-yellow mass of cells that seals over the break and begins producing progesterone. Progesterone is the hormone that thickens and enriches the uterine lining, preparing it to support a potential pregnancy. The corpus luteum also produces some estrogen. If pregnancy doesn’t occur, the corpus luteum breaks down after about 10 to 14 days, progesterone drops, and your period starts.
Your Fertile Window
A released egg survives for less than 24 hours. That sounds like a tiny window, but the fertile period is actually wider than that because sperm can survive inside the cervix, uterus, and fallopian tubes for 3 to 5 days. This means you can conceive from sex that happened several days before ovulation, not just on the day of ovulation itself. In practical terms, your fertile window spans roughly six days: the five days leading up to ovulation plus the day of ovulation.
If you’re trying to get pregnant, the most fertile days are the two to three days before ovulation, when sperm are already in place and waiting. If you’re trying to avoid pregnancy, you need to account for this longer survival window rather than focusing only on the day of egg release.
Signs You Can Track
Your body offers several clues that ovulation is approaching or has just occurred. The most reliable one you can observe at home is changes in cervical mucus. In the days before ovulation, your discharge becomes wetter, more slippery, and stretchy, often compared to the look and feel of raw egg whites. This type of mucus helps sperm travel more efficiently. After ovulation, mucus typically becomes thicker and less noticeable.
Your basal body temperature (your temperature at complete rest, taken first thing in the morning) also shifts after ovulation. It rises slightly, typically less than half a degree Fahrenheit (about 0.3°C), and stays elevated until your next period. The catch is that this rise happens after ovulation, so it confirms that ovulation occurred but doesn’t predict it in advance. Tracking it over several months, though, can help you recognize your personal pattern.
Some people also notice breast tenderness, mild bloating, or a brief increase in sex drive around ovulation. These vary widely from person to person and cycle to cycle.
Ovulation Pain
About one in five women feel a distinct pain around ovulation, sometimes called mittelschmerz (German for “middle pain”). It’s typically a one-sided ache or sharp twinge low in the pelvis, on whichever side the egg was released. The discomfort has two likely causes: the stretching of the ovary’s surface as the follicle grows, and the irritation caused by fluid or blood leaking from the ruptured follicle.
For most people, it lasts anywhere from a few minutes to a few hours. In some cases, it can persist for up to 24 to 48 hours. The pain usually doesn’t require treatment and resolves on its own. It can switch sides from month to month depending on which ovary ovulates.
When Ovulation Doesn’t Happen
Not every cycle includes ovulation. When an egg isn’t released, it’s called anovulation, and it’s more common than many people realize. Hormone imbalances are the most frequent cause. Polycystic ovary syndrome (PCOS) accounts for about 70% of anovulation cases. In PCOS, the body produces excess androgens, which prevent follicles in the ovaries from maturing enough to release an egg.
Other factors that can prevent ovulation include having a very low body mass index (often linked to eating disorders or excessive exercise), obesity (which can also raise androgen levels), high stress, and the natural transitions at either end of reproductive life. If you’ve recently started getting periods or are approaching menopause, irregular or absent ovulation is expected. Primary ovarian insufficiency, a condition where the ovaries stop functioning normally before age 40, is another cause.
You can still have a period without ovulating. These anovulatory cycles often involve irregular bleeding patterns, but they can sometimes look like a normal period, making it difficult to know ovulation was skipped without tracking signs like basal body temperature or using ovulation test kits.