📅 Ovulation Calculator

About this calculator

This calculator estimates your fertile window from your menstrual cycle. Enter the first day of your last period and your average cycle length, and it projects ovulation day (roughly 14 days before your next period) plus the five fertile days leading up to it, when conception is most likely.

The logic counts forward one cycle length from your last period to predict the next, then subtracts about 14 days — the relatively stable luteal phase. The fertile window covers the five days before ovulation plus ovulation day itself, since sperm can survive up to five days.

Tip: This is an estimate, not contraception and not a fertility guarantee — cycles vary and stress shifts ovulation, so confirm with ovulation test strips or a clinician for important decisions.