There are many ways to calculate the day of ovulation, such as projecting it from the menstrual cycle, ultrasound test, ovulation test paper test and so on. Ovulation is an important factor in pregnancy, want to calculate the day of ovulation for regular menstruation for women can be deduced from the menstrual cycle, that is, in the next menstrual period about 14 days before the onset. For irregular menstruation can be tested every day after menstruation with ovulation test paper, as long as the test to two red lines is close to ovulation; want to be more accurate can be in the next day after menstruation to the hospital ultrasound to monitor follicle condition. Ovulation is the best window to get pregnant, so if you want to get pregnant, you can make reasonable arrangements for coitus at the time of ovulation.