A released egg survives for less than 24 hours after ovulation, and its best window for fertilization is even shorter. The highest pregnancy rates occur when sperm meets the egg within 4 to 6 hours of its release from the ovary. After that narrow peak, the egg’s ability to be fertilized drops steadily until it breaks down entirely.
The Egg’s Lifespan After Release
Once the ovary releases an egg, it enters the fallopian tube and begins a slow journey toward the uterus. During this transit, the egg is open to fertilization, but the clock is ticking. Most sources cite a maximum lifespan of 12 to 24 hours, though the realistic fertilization window is closer to 12 hours for many women. By the time the egg has been in the fallopian tube for a full day without being fertilized, it has already started to degrade and will be absorbed by the body.
This is a stark contrast to sperm, which can survive inside the female reproductive tract for up to five days. That difference is the entire reason the fertile window extends well before ovulation day itself.
Why the Fertile Window Is Six Days, Not One
The American Society for Reproductive Medicine defines the fertile window as the six-day interval ending on the day of ovulation. That means the five days leading up to ovulation plus ovulation day itself. Sperm deposited days before the egg is released can still be alive and waiting in the fallopian tubes when the egg arrives.
Research on conception timing shows that the likelihood of pregnancy is actually greatest when intercourse occurs the day before ovulation, not the day of ovulation. By the time you know ovulation has happened, the egg may already be several hours old, and its fertilization potential is declining. This is why trying to conceive only after confirming ovulation often means missing the best window.
From LH Surge to Egg Release
If you use ovulation predictor kits, you’re detecting the surge of luteinizing hormone (LH) that triggers the ovary to release the egg. Ovulation typically happens between 8 and 20 hours after LH reaches its peak. A positive test strip means ovulation is approaching but hasn’t necessarily happened yet, which is exactly why it’s useful. It gives you a heads-up while the egg is still on its way, rather than after it’s already aging in the fallopian tube.
Keep in mind that the test detects the surge, not the peak. LH can rise for several hours before hitting its highest point, so ovulation may occur a bit later than you expect from the first positive reading. The practical takeaway: a positive ovulation test means the next 24 to 36 hours are your most fertile, and acting on it promptly gives sperm time to reach the fallopian tube before or right as the egg arrives.
How Your Body Signals the Window Has Closed
After ovulation, your body shifts gears. Progesterone levels rise, and one of the most noticeable effects is a change in cervical mucus. In the days leading up to ovulation, cervical mucus becomes clear, slippery, and stretchy, often compared to raw egg whites. This type of mucus helps sperm travel efficiently toward the egg.
Once the egg has been released and the fertile window closes, cervical mucus thickens and dries up. It stays that way for the rest of the cycle until menstruation. If you’re tracking mucus changes, a sudden shift from wet and stretchy to thick and tacky is a reliable signal that ovulation has already passed and the egg’s viability window is over.
What Happens If the Egg Isn’t Fertilized
An unfertilized egg doesn’t sit around for long. Within about 24 hours of release, it begins to break apart. The outer layer hardens, making sperm penetration increasingly unlikely even before the egg fully degrades. The remnants are reabsorbed by the lining of the fallopian tube or pass into the uterus, where they disintegrate along with the uterine lining during menstruation roughly two weeks later.
Meanwhile, the follicle that released the egg transforms into a temporary structure called the corpus luteum, which produces progesterone to prepare the uterine lining for a potential pregnancy. If no fertilized egg implants, the corpus luteum shrinks after about 10 to 14 days, progesterone drops, and your period begins.
Practical Timing for Conception
Because the egg’s viable hours are so limited, the most effective strategy for conception is having sperm already in position before ovulation occurs. Couples trying to conceive generally have the best odds with intercourse every one to two days during the five days before ovulation and on ovulation day itself. Waiting until after ovulation to start trying cuts into an already short window.
For the same reason, natural family planning methods that rely on avoiding intercourse only on ovulation day are less reliable. Sperm from intercourse five days earlier can still fertilize a newly released egg. The egg’s short lifespan is only half the equation. The sperm’s long survival is the other half, and both matter when planning or preventing pregnancy.