What Is the Fertile Window?
The fertile window is the period during which pregnancy is most likely to occur. Ovulation typically happens 14 days before the next period, meaning in a 28-day cycle, it occurs around day 14. Sperm can survive in the reproductive tract for up to 5 days, while an egg remains viable for 12–24 hours after ovulation. This makes the 5 days leading up to ovulation and the day of ovulation itself the most fertile period.
This calculator uses the standard LMP (Last Menstrual Period) method combined with your cycle length to estimate your ovulation date and fertile window. Since individual cycles vary, these results are estimates. For precise ovulation tracking, consider using ovulation predictor kits (OPK) that detect the LH surge, or consult a healthcare provider for ultrasound monitoring.
Frequently Asked Questions
The 5 days before ovulation and the day of ovulation itself represent your peak fertile window. Sperm can survive up to 5 days, so having intercourse in this window maximizes conception chances.
Ovulation date = LMP + (cycle length − 14). For a 28-day cycle, ovulation occurs on day 14. The "-14" accounts for the luteal phase, which is relatively constant at ~14 days.
Use the average of several recent cycles as your cycle length. For irregular cycles, ovulation predictor kits or tracking basal body temperature can provide more accurate results.