A human egg survives for 12 to 24 hours after ovulation. That’s the entire window in which it can be fertilized by sperm. The highest pregnancy rates occur when sperm meets the egg within 4 to 6 hours of its release, meaning the practical window for conception is even shorter than most people realize.
Why the Window Is So Short
Once your ovary releases an egg, it travels into the fallopian tube and begins to degrade almost immediately. Unlike sperm, which can survive in the reproductive tract for two to three days (and potentially up to a week), the egg has no ability to sustain itself for long outside the follicle. After roughly 24 hours, it can no longer be fertilized and is absorbed by the body.
This is why timing matters so much for conception. The egg doesn’t wait. If sperm isn’t already present in the fallopian tube or doesn’t arrive within that narrow window, fertilization won’t happen during that cycle.
The 4-to-6-Hour Sweet Spot
While the egg technically remains viable for up to 24 hours, its quality declines over that period. The highest pregnancy rates are reported when the egg and sperm join within 4 to 6 hours of ovulation. After that, the chances drop steadily. By the time you’re approaching the 24-hour mark, fertilization is still possible but significantly less likely.
This is one reason why having sperm already waiting in the fallopian tubes before ovulation occurs is more effective than trying to time intercourse for after the egg is released. Sperm need time to travel through the cervix and uterus, and that journey alone can take hours.
Your Fertile Window Is Wider Than You Think
Even though the egg only lives for about a day, your overall fertile window spans roughly five to six days per cycle. That’s because sperm can survive in the reproductive tract for an average of two to three days, with some surviving up to a week. Sperm that arrives days before ovulation can still be alive and capable of fertilizing the egg the moment it’s released.
This means the days leading up to ovulation are actually your most fertile. Having intercourse one or two days before you ovulate gives sperm time to reach the fallopian tube and be ready when the egg appears. Waiting until after ovulation to have intercourse leaves very little margin, since you’re racing against a clock that started the moment the egg was released.
Pinpointing When Ovulation Happens
Knowing the egg’s lifespan is only useful if you can identify when ovulation actually occurs. Most people track ovulation using one of a few methods: LH test strips, basal body temperature, or cervical mucus changes.
LH test strips detect a surge in luteinizing hormone that triggers ovulation. After this hormone appears in your blood, ovulation typically happens 36 to 40 hours later. Since urine tests pick up LH slightly after blood levels rise, a positive urine test usually means ovulation will occur within 12 to 24 hours. That positive result is your signal that the fertile window is open and closing fast.
Basal body temperature tracking works differently. Your resting temperature rises slightly after ovulation has already occurred, so it confirms ovulation after the fact rather than predicting it in advance. Over several cycles, though, it helps you identify patterns in your timing.
Does Age Affect Egg Viability?
Age doesn’t appear to shorten the 12-to-24-hour survival window in a meaningful way, but it does affect the quality of the egg that’s released. You’re born with a fixed number of eggs, and both the quantity and quality decline over time. By age 30, fertility begins to drop, and the decline accelerates in the mid-30s.
The issue isn’t that older eggs die faster after ovulation. It’s that the eggs themselves are more likely to carry abnormal chromosomes, which reduces the chance of successful fertilization and healthy implantation. So while the clock runs for the same number of hours regardless of age, the odds of that egg leading to a pregnancy are lower with each passing year. These changes happen faster than most people expect, and they’re invisible, with no symptoms or signs you can feel.
Practical Takeaways for Timing
If you’re trying to conceive, the most effective strategy is to have intercourse in the one to two days before ovulation rather than waiting for ovulation day itself. Sperm that’s already in the fallopian tube has the best chance of meeting the egg during its peak viability, within those first few hours after release.
If you’re trying to avoid pregnancy, remember that the egg’s short lifespan doesn’t make the fertile window short. Sperm deposited days before ovulation can still result in pregnancy. The combined survival times of sperm and egg create a fertile window that’s much larger than the egg’s 12-to-24-hour life might suggest.