Ovulation occurs 14 days before menstruation, which is about 14 days after ovulation. If menstruation is regular, you can guess which day you will ovulate. If periods are irregular, there is no way to accurately predict ovulation. The only way to monitor ovulation is to take your basal body temperature or ovulation test strips, or you can go to the hospital and have an ultrasound to monitor which day you are ovulating. If the menstrual cycle is more regular, the menstrual cycle is about 28-30 days, probably the ovulation date is in the middle of two menstrual periods. However, the ovulation period is not fixed, and can change with emotional changes or environmental changes. Therefore, if you do not want to have children, it is best not to use safe period contraception to avoid accidental pregnancy.