A woman is most fertile during the ovulation phase of her menstrual cycle. Ovulation typically occurs around the middle of the cycle, usually about 14 days before the start of the next menstrual period. For a woman with a regular 28-day cycle, this means ovulation generally happens around day 14. However, the exact timing can vary among women and across different cycles. The fertile window—the time when pregnancy is most likely to occur—is usually the three days leading up to and including the day of ovulation. Sperm can survive for up to five days inside the female reproductive tract, so having sex during the days before ovulation increases the chance of fertilization. After ovulation, the egg is viable for about 12-24 hours. So, if a woman has a 28-day cycle, the most fertile days are approximately days 12, 13, and 14 of the cycle. For cycles of different lengths, ovulation generally occurs about 14 days before the next period, and the fertile window shifts accordingly. In summary:

• Ovulation occurs about 14 days before the next period.
• The fertile window is roughly the 5 days before ovulation plus the day of ovulation.
• The highest fertility is in the 3 days leading up to and including ovulation.
• Sperm can survive up to 5 days, but the egg lasts about 12-24 hours after ovulation.

If menstrual cycles are irregular, tracking methods like basal body temperature, ovulation predictor kits, or menstrual cycle tracking can help estimate ovulation more accurately.