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, so timing matters more than most people realize.
Why the Egg’s Lifespan Is So Short
Once the 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 up to five days, the egg has no way to sustain itself for long outside the follicle. If fertilization doesn’t happen within roughly 12 to 24 hours, the egg breaks down, gets absorbed by the body, and is shed along with the uterine lining during your next period.
After the egg is gone, the empty follicle transforms into a structure that pumps out progesterone. Progesterone levels climb for about five days after ovulation before dropping back down. This hormonal shift is what triggers premenstrual symptoms and, if no pregnancy occurs, eventually your period.
The Fertile Window Is Wider Than You Think
Even though the egg itself only lasts about a day, your actual fertile window spans roughly six days per cycle. That’s because sperm can live inside the reproductive tract for up to five days. So intercourse that happens several days before ovulation can still result in pregnancy if those sperm are waiting in the fallopian tube when the egg arrives.
The math works out like this: five days of possible sperm survival before ovulation, plus the single day the egg remains viable afterward. The American College of Obstetricians and Gynecologists puts it simply: you can conceive from sex up to five days before ovulation or one day after. For the best chance of pregnancy, having sex every day or every other day during this six-day window is what research supports.
Peak Timing for Conception
Not all days in the fertile window carry equal odds. The two days with the highest conception rates are the day before ovulation and the day of ovulation itself. This is when sperm are most likely to encounter a freshly released egg. The best pregnancy rates have been reported when egg and sperm meet within four to six hours of the egg’s release, so the closer to ovulation, the better.
Sex that happens three to five days before ovulation can still lead to pregnancy, but the probability drops with each earlier day because fewer sperm remain viable by the time the egg appears.
How to Know When You’re Ovulating
Since the egg’s window is so narrow, pinpointing ovulation gives you a real advantage whether you’re trying to conceive or trying to avoid it. Ovulation happens about 36 to 40 hours after a sharp rise in luteinizing hormone, commonly called the LH surge. This is exactly what home ovulation predictor kits detect. A positive result on one of these tests means ovulation is likely within the next day and a half.
Other signs that ovulation is approaching include a change in cervical mucus (it becomes clear, slippery, and stretchy, similar to raw egg whites), a slight rise in basal body temperature, and mild pelvic discomfort on one side. The temperature shift, though, only confirms ovulation after it’s already happened, so it’s more useful for tracking patterns over multiple cycles than for catching the current one in time.
What This Means If You’re Trying to Conceive
Because the egg deteriorates so quickly, the most effective strategy is to have sperm already in the fallopian tube before ovulation occurs. Waiting until you’re sure you’ve ovulated often means the window has already closed or is closing. Starting intercourse a few days before your expected ovulation date and continuing through the day after gives you the broadest coverage of that six-day fertile window.
If you’ve been tracking your cycles and notice consistent patterns, you can narrow the timing further. But even with perfect tracking, ovulation can shift by a day or two from cycle to cycle, which is why spacing intercourse across several days works better than trying to hit one exact moment.
What This Means If You’re Avoiding Pregnancy
The short lifespan of the egg can be misleading. It’s tempting to think that pregnancy is only possible for one day per cycle, but the five-day survival of sperm extends the risk zone significantly. Unprotected sex five days before ovulation still carries a real chance of pregnancy. And because ovulation timing can vary, even in people with regular cycles, the “safe” days are harder to identify than they appear on a calendar.