Conception probability is highest in the 1 to 2 days leading up to ovulation (34% to 42% chance) and on ovulation day itself (33%). Because sperm can live for up to 5 days inside healthy cervical mucus, having intercourse during this 6-day fertile window is critical for optimizing pregnancy chances.

The luteal phase is the period of time between your ovulation day and the start of your next period. While standard calculators assume a generic 14-day luteal phase, individual phases can range between 10 and 16 days. Overriding this value with your specific phase duration is vital to pin down the exact day of ovulation.

The Shettles Method is a timing theory based on sperm physical traits. Y-bearing sperm (male) are smaller, faster, but less resilient, meaning having intercourse very close to or on ovulation day theoretically favors them. X-bearing sperm (female) are larger and slower but survive longer in acidic vaginal secretions, meaning having intercourse 3 to 5 days before ovulation theoretically favors their resilience. This is a statistical theory and not a clinical guarantee.