The calculation of menstrual ovulation period needs to be based on the menstrual cycle. In other words, if the menstrual cycle is 28 days, ovulation on the 12th will be on the 26th day of the month; if the menstrual cycle is 30 days, ovulation on the 12th will be on the 28th day of the month; if the menstrual cycle is 35 days, ovulation on the 12th will be on the 3rd day of the following month, and so on. As the follicles mature, they gradually move toward the surface of the ovary and protrude outward. As the follicle approaches the surface of the ovary, the superficial cells there become thinner and finally rupture. After most of the follicular fluid flows out, the oocytes are expelled, which is called ovulation. The day of ovulation is usually the 14th day before the next menstrual period, and the 5 days before and 4 days after the day of ovulation are the period of ovulation, so together with the day of ovulation, there are 10 days of ovulation. Ovulation can usually be monitored by ultrasound and other tests. Ovulation is also known as the fertile period and the risk period. Having intercourse during this period increases the probability of conception, so for couples who want to use contraception, they should use good contraception during this period.