Ovulation itself is a brief event. The actual release of an egg from the ovary takes only a few minutes, and once released, the egg survives for 12 to 24 hours. That short window is the only time fertilization can occur. But the full picture of fertility around ovulation is more nuanced, which is why the answer matters whether you’re trying to conceive or trying to avoid it.
The Egg’s Lifespan After Release
Once the ovary releases an egg, it travels into the fallopian tube and remains viable for roughly 12 to 24 hours. If sperm don’t reach and fertilize the egg within that window, it begins to break down and is eventually absorbed by the body. This is why timing matters so much for conception: the egg’s availability is measured in hours, not days.
Your Fertile Window Is Longer Than Ovulation
While the egg only lasts about a day, sperm can survive inside the cervix, uterus, and fallopian tubes for 3 to 5 days. That means intercourse several days before ovulation can still result in pregnancy, because sperm may already be waiting when the egg arrives. In practical terms, the fertile window spans about six days: the five days leading up to ovulation plus the day of ovulation itself.
This distinction is important. Many people conflate “ovulation” with “the fertile window,” but they’re very different. Ovulation is a single-day biological event. The fertile window is the broader stretch of time when pregnancy is possible.
When Ovulation Actually Happens in Your Cycle
The textbook answer is day 14 of a 28-day cycle, but real cycles are far less predictable. A 2024 study in Human Reproduction tracked 676 ovulatory cycles in healthy women and found that the follicular phase (the stretch from your period to ovulation) generally ranged from 12 to 26 days. The luteal phase (from ovulation to your next period) ranged from 4 to 16 days, with a median of about 11 days. The researchers specifically noted that the luteal phase “is not predictably 13 to 14 days long,” which is what many fertility resources assume.
What this means for you: even if your cycle is a consistent 28 days, ovulation might happen on day 12 one month and day 18 the next. Relying on calendar counting alone is unreliable for pinpointing ovulation.
What Triggers Ovulation
Ovulation is triggered by a surge in luteinizing hormone, commonly called LH. This surge signals the ovary to release a mature egg. The physical release of the egg typically happens 8 to 20 hours after LH reaches its peak. Home ovulation predictor kits detect this LH surge in urine and will show a positive result roughly 12 to 48 hours before ovulation occurs. A positive test doesn’t mean you’re ovulating right now. It means ovulation is approaching.
How to Track Ovulation
Cervical Mucus
In the days leading up to ovulation, cervical mucus becomes clear, slippery, and stretchy, often compared to raw egg whites. This “peak day” of mucus closely tracks with ovulation. Research from Marquette University found that the peak mucus day falls within 3 days of the estimated ovulation day about 97 to 100% of the time. In most cycles (72%), the peak mucus day comes before or on the day of ovulation, making it a useful forward-looking signal.
After the peak day passes, mucus becomes thicker and stickier. If you count 4 full days after the peak mucus day, you’ll be in the infertile phase of your cycle about 99% of the time.
Basal Body Temperature
Your resting body temperature rises slightly after ovulation, driven by the increase in progesterone. Research shows the first noticeable temperature rise occurs about 8 hours after ovulation, with a delay of 24 to 36 hours relative to progesterone increases. The catch is that this shift only confirms ovulation after it has already happened, so it’s useful for confirming a pattern over several cycles rather than predicting ovulation in real time.
Ovulation Predictor Kits
These urine-based tests detect the LH surge and give you a heads-up that ovulation is likely within the next day or two. They’re the most practical tool for predicting ovulation before it happens, though they tell you about the hormonal trigger rather than confirming the egg has actually been released.
Combining all three methods, mucus for advance warning, an OPK for confirmation of the surge, and temperature for retrospective proof, gives the most complete picture of your ovulation timing.
How Ovulation Changes With Age
During perimenopause, which can begin in your mid-to-late 30s or 40s, ovulation becomes less regular. You may skip ovulation entirely in some cycles, meaning no egg is released at all. Cycles may become shorter or longer, and flow can vary significantly from month to month. The egg itself doesn’t last longer or shorter with age, but the unpredictability of whether and when ovulation occurs makes tracking much harder. This is a major reason fertility declines before menstruation actually stops.
Signs That Ovulation Is Happening
Some people feel ovulation. A mild, one-sided lower abdominal ache (sometimes called mittelschmerz) can occur when the egg is released. Light spotting is possible. Breast tenderness, a heightened sense of smell, and increased sex drive are also commonly reported around ovulation, all driven by the same hormonal shifts that trigger the egg’s release.
Not everyone notices these signs, and their absence doesn’t mean you’re not ovulating. They’re supporting clues rather than reliable indicators on their own.