Egg Viability After Ovulation
The egg remains viable for fertilization for approximately 12-24 hours after ovulation, with the most commonly cited estimate being less than 24 hours. 1, 2
Biological Window for Fertilization
The evidence indicates a remarkably narrow window of egg viability:
Sperm must encounter the egg within 24 hours after ovulation for fertilization to occur, as spermatozoa normally reach the fertilization site in the fallopian tube within this timeframe 2
The ovum survival time is estimated at 0.7 days (approximately 17 hours), based on mathematical modeling of conception probability across the menstrual cycle 1
Fertilization typically occurs within 12-24 hours post-ovulation, after which the egg degenerates and can no longer be fertilized 3, 1
The Fertile Window Context
Understanding egg viability requires context about the broader fertile period:
The fertile window extends 5 days before ovulation through the day of ovulation itself, with conception probabilities significantly different from zero during this 6-day span 1
Sperm survival is considerably longer than egg survival, with an average of 1.4 days but capable of surviving up to 4.4 days (5% probability) or even 6.8 days (1% probability) in the female reproductive tract 1
The highest probability of conception occurs when intercourse happens 1-2 days before ovulation, not on the day of ovulation itself, because sperm need time to capacitate and reach the fertilization site 1
Clinical Implications
The short egg viability window has important practical consequences:
Timing intercourse or insemination after ovulation has already occurred significantly reduces conception probability, as the egg may already be degenerating 4, 1
For intrauterine insemination (IUI), the procedure should be performed 24-40 hours after hCG trigger or 1 day after LH surge, ensuring sperm are present when ovulation occurs rather than waiting until after 4
Spermatozoa can reach the fallopian tube within 10 minutes of insemination, but they require additional time for capacitation before they can fertilize the egg 5, 4
Common Pitfalls
Women frequently misestimate their ovulation day, which can lead to mistimed intercourse:
Only 12.7% of women correctly estimated their ovulation day in a study of women trying to conceive, with a median error of +2 days 6
Only 55% of estimated ovulation days fell within the actual fertile window, and only 27% occurred on days of peak fertility 6
The most common assumption is that ovulation occurs on day 14, but ovulation timing varies widely between days 9-20 in a typical 28-day cycle 7, 8