Ovulation usually occurs about 14 days before menstruation, and if the menstrual cycle is more regular, at 28-30 days, and the last menstrual period is on the 24th, ovulation will occur around the 10th. Because ovulation occurs over a period of three days, it is possible that you may be ovulating between the 10th and 13th, and the chances of pregnancy may be greatly increased if you have intercourse at this time. If there is irregularity in the menstrual cycle, the ovulation period will also advance with the advancement of menstruation, and with the postponement of menstruation will cause the ovulation period to be pushed back. At the same time, if you want to accurately determine the time of ovulation, it is recommended to start counting from the first day of menstruation, the 11th day of the drugstore to buy ovulation test paper, you can test in the ovulation period, until the appearance of a strong positive is in the ovulation period, you can be in the coitus, the chances of conception may be more accurate.