Ovulation happens about 14 days before your period starts. If your average menstrual cycle is 28 days, you ovulate around day 14, and your most fertile days are days 12, 13 and 14. If your average menstrual cycle is 35 days ovulation happens around day 21 and your most fertile days are days 19,20 and 21.

How many days after your period are you the most fertile?

Your menstrual cycle begins on the first day of your period and continues up to the first day of your next period. You're most fertile at the time of ovulation (when an egg is released from your ovaries), which usually occurs 12 to 14 days before your next period starts.

How do you calculate your fertile days?

The length of your menstrual cycle is the number of days from the first day of bleeding in your last period, to the first day of bleeding in your next. From this figure, subtract 14 days from the end of your current cycle to determine the approximate day you ovulate.