After ovulation, an egg remains viable for 12 to 24 hours. That’s the entire window in which fertilization can occur. If sperm don’t reach the egg within that timeframe, your body reabsorbs it and conception isn’t possible until the next cycle.
That narrow window is surprisingly short, but the practical fertile window is actually much wider, thanks to how long sperm can survive inside the reproductive tract.
What Happens During Those 12 to 24 Hours
When an ovary releases an egg, it enters the fallopian tube and begins traveling toward the uterus. During this journey, the egg is capable of being fertilized, but its quality starts declining almost immediately. The highest pregnancy rates occur when sperm meet the egg within four to six hours of ovulation, according to data from MedlinePlus. After that early peak, the odds of successful fertilization drop steadily.
By around 12 hours, the egg’s ability to be fertilized is significantly reduced. By 24 hours, it’s essentially gone. Your body breaks it down and reabsorbs the cellular material. There’s no pain or noticeable physical sign when this happens.
Why the Fertile Window Is Longer Than 24 Hours
If the egg only lasts a day at most, you might wonder how anyone gets pregnant without perfectly timed intercourse. The answer is sperm longevity. Motile sperm can survive in the female reproductive tract for up to five days. That means sperm from intercourse that happened days before ovulation can still be waiting in the fallopian tube when the egg arrives.
This creates a fertile window of roughly five to six days each cycle: the five days leading up to ovulation plus the day of ovulation itself. Intercourse on any of those days gives sperm a chance to be in position when the egg is released. One large study estimated about a 3% chance of conception from intercourse six days before ovulation, with odds climbing as ovulation approaches. By one day after ovulation, the chance drops to around 1%, because the egg is already deteriorating.
Timing Intercourse for Conception
Because the egg’s window is so short, the most effective strategy for conception is having sperm already present before the egg arrives. The one or two days immediately before ovulation are statistically the most fertile. Intercourse on the day of ovulation itself also works well, especially if it happens early enough for sperm to reach the egg within those critical first hours.
Waiting until after you’ve confirmed ovulation is risky timing. By the time ovulation test strips show a positive result or you notice a basal body temperature shift, the clock is already running on those 12 to 24 hours. If you’re trying to conceive, the days before ovulation matter more than the day after.
Why It’s Only One Egg Per Cycle
In most cycles, only one egg is released. Occasionally two eggs are released (which is how fraternal twins happen), but each egg has the same 12 to 24 hour lifespan. There’s no cumulative effect where multiple eggs extend the window. If two eggs are released, they typically come out within 24 hours of each other, so the overall fertile window doesn’t meaningfully change.
How Age Affects Egg Quality Within the Window
The 12 to 24 hour viability window stays roughly the same regardless of age, but the quality of the egg inside that window changes. As you get older, eggs are more likely to have chromosomal abnormalities, which means even if fertilization happens within the viable timeframe, the chances of a successful pregnancy are lower. This is separate from the lifespan question. A 38-year-old’s egg doesn’t expire faster than a 25-year-old’s, but it may be less likely to result in a healthy embryo even when everything else goes right.
If You’re Trying to Avoid Pregnancy
The short lifespan of the egg can be misleading if you’re using fertility awareness to prevent pregnancy. While the egg itself only survives up to 24 hours, sperm deposited days earlier can still cause conception. Unprotected intercourse five days before ovulation carries real pregnancy risk. And because ovulation timing can shift from cycle to cycle due to stress, illness, or hormonal fluctuations, pinpointing the exact day isn’t always reliable. The egg’s brief viability does not mean the risk of pregnancy is confined to a single day.