If you usually have regular menstruation with a cycle of 28-30 days and your period comes on the 28th, ovulation is around the 14th of each month; if your period is irregular, ovulation is also not accurate and may be early or delayed. Generally, the ovulation day is around the 14th day before the next menstruation, because the luteal recession will come 12-14 days after the follicles mature and expel. Usually the 4 days before and 5 days after the day of ovulation, together with the day of ovulation, is the ovulation period, usually about 10 days. Sperm can survive in the uterus for 2-3 days. If you have intercourse during the ovulation period without contraception, there is a possibility of unwanted pregnancy. If you have regular periods, you can take contraceptive measures with reference to the ovulation period. If you have irregular periods, it is recommended to use effective contraceptive measures, such as intrauterine devices or condoms. Ovulation may fluctuate due to diet, sleep, illness, emotions, etc. This is generally normal and not a cause for concern.