Ovulation Calculator

It estimates ovulation as roughly 14 days before your next period. From the first day of your last period and your average cycle length, it finds the next period, subtracts 14 days for the likely ovulation date, and marks the fertile window as the five days before plus the day of ovulation.

Your fertile window spans the five days leading up to ovulation and ovulation day itself — about six days total. The two days before ovulation and the day of ovulation are usually the most fertile, because sperm can survive up to five days while the egg lives about 24 hours.

It's an estimate based on calendar averages and assumes a fairly regular cycle. Actual ovulation can shift with stress, illness, or cycle irregularity. For more precision, combine it with basal body temperature tracking, cervical mucus changes, or ovulation predictor kits.

It's much less likely but not impossible, since cycle timing varies and sperm can survive several days. If you're avoiding pregnancy, calendar timing alone isn't a reliable contraceptive method.

Calendar-based estimates are less reliable with irregular cycles. Track several cycles to find your average length, and consider basal body temperature or ovulation test kits, which detect the hormone surge directly rather than relying on dates.