If you have your period on the 18th, if your period is regular and your cycle is 30 days, ovulation is from the 29th of last month to the 8th of this month, and these 10 days belong to the ovulation period. However, some people have long menstrual cycles and some have short menstrual cycles, which are between 28-30 days. In case of regular menstruation, the 14th day belongs to the day of ovulation on the 1st day before the next menstrual period, and the 5 days before and the 4 days after the day of ovulation belong to the ovulation period, which can be calculated according to the menstrual cycle. If you have irregular menstruation and cannot accurately calculate ovulation through menstruation, you need to use ovulation test strips or ultrasound for monitoring, which is relatively accurate. If you intend to get pregnant, it is recommended to arrange intercourse during ovulation, preferably on alternate days, and not too often to avoid overexertion that may affect conception. If you do not intend to get pregnant, you can use a condom or an IUD to prevent pregnancy.