When is ovulation on the 29th menstrual period is related to the individual patient’s situation and should be analyzed on a case-by-case basis, not as a generalization. If the patient has a regular menstrual cycle with the same volume, number of days and color of each period, and the menstrual cycle is 30 days, then ovulation should occur on the 12th-20th day of the menstrual cycle, i.e. the 10th-20th day of the next month. If the patient has irregular menstruation, ovulation cannot be predicted. Patients are advised to test ovulation by themselves with ovulation test paper. If the ovulation test paper is positive, it means ovulation is in progress. In addition, patients can also go to the hospital to monitor the follicle development under ultrasound. A follicle development between 18-22mm is a mature follicle and the chances of pregnancy are higher than usual. The period 1 week before the onset of menstruation and within 1 week after the next menstrual period are relatively safe periods and are not susceptible to conception, but it is still necessary to use contraception to prevent unwanted pregnancies.