Ovulation itself is a brief event. The egg survives for less than 24 hours after it’s released from the ovary, making the actual window for fertilization surprisingly short. But the broader fertile window, which is what most people really want to know about, stretches to about six days when you factor in how long sperm can survive in the reproductive tract.
How Long the Egg Survives
Once your ovary releases an egg, it has fewer than 24 hours to be fertilized. After that, the egg begins to break down and is no longer viable. This is why the timing of ovulation matters so much for both conception and contraception. The egg’s short lifespan means your body’s actual “ovulation period” is measured in hours, not days.
The Fertile Window Is Longer Than Ovulation
Sperm can survive inside the reproductive tract for up to five days under the right conditions. That means sex five days before ovulation can still result in pregnancy, because sperm may be waiting in the fallopian tubes when the egg arrives. Combined with the egg’s own survival time, this creates a fertile window of roughly six days: the five days leading up to ovulation plus the day of ovulation itself.
Not all days in that window carry equal odds. The probability of conception peaks in the two days before ovulation. Having sex two days before ovulation gives about a 26% chance of pregnancy per cycle. By contrast, sex the day after ovulation drops the odds to just 1%, according to data from the British Fertility Society. This steep drop-off reflects how quickly the egg deteriorates once released.
What Triggers Ovulation
Ovulation doesn’t happen randomly. It’s triggered by a sharp rise in luteinizing hormone, commonly called the LH surge. This surge begins about 36 to 40 hours before the egg is actually released, which is why at-home ovulation test strips (which detect LH in urine) can give you advance warning that ovulation is approaching. A positive result generally means you’re within a day or two of releasing an egg.
How to Tell When You’re Ovulating
Cervical Mucus Changes
Your cervical mucus follows a predictable pattern through your cycle. In the days after your period, discharge tends to be dry or tacky. As ovulation approaches, it gradually becomes wetter and creamier. The clearest signal comes in the three to four days closest to ovulation, when mucus turns slippery, stretchy, and resembles raw egg whites. In a typical 28-day cycle, this fertile-quality mucus shows up around days 10 to 14. After ovulation, mucus dries up again and stays that way until your next period.
Basal Body Temperature
Your resting body temperature rises slightly after ovulation, typically by 0.4 to 1.0 degrees Fahrenheit. The shift is small enough that you need a sensitive thermometer and consistent morning measurements (before getting out of bed) to detect it. When you see higher temperatures for at least three consecutive days, you can reasonably confirm that ovulation has already occurred. The catch is that this method tells you after the fact. It’s useful for understanding your cycle patterns over time but won’t alert you before ovulation happens the way LH strips or mucus tracking can.
When Ovulation Happens in Your Cycle
You may have heard that ovulation always occurs on day 14 of a 28-day cycle, with a luteal phase (the stretch between ovulation and your next period) that’s reliably 13 to 14 days long. Recent research paints a different picture. A yearlong study tracking healthy women with normal cycle lengths found that luteal phase lengths ranged from as short as 3 days to as long as 16 days, with a median of 11 days. Even within the same woman, the luteal phase varied by about 3 days from cycle to cycle.
What this means practically: ovulation day can shift around, even if your periods seem regular. In a 28-day cycle, ovulation might happen on day 12 one month and day 16 the next. If you’re relying on calendar-based predictions alone, you could easily miss or misjudge your fertile window. Combining multiple tracking methods (mucus observation, LH testing, and temperature charting) gives a much more reliable picture.
When Ovulation Doesn’t Happen
Not every cycle produces an egg. Cycles without ovulation, called anovulatory cycles, are common enough to account for about 30% of infertility cases. The most frequent cause is polycystic ovary syndrome (PCOS), which is responsible for roughly 70% of anovulation cases. PCOS causes elevated levels of androgens that prevent follicles in the ovaries from maturing enough to release an egg.
Other factors that can temporarily suppress ovulation include very high or very low body weight, intense exercise routines, and significant stress. These don’t permanently damage your ability to ovulate. Reducing exercise intensity, reaching a healthier weight, or managing stress can often restore regular ovulation without medical intervention. If you’re tracking your cycle and consistently see no temperature shift, no fertile-quality mucus, or irregular periods, those are signs ovulation may not be occurring.