When is the 20th menstrual period ovulation, there are individual differences, related to the regularity of women’s menstrual cycle, should be a specific analysis of the problem, not a generalization. In general, ovulation is 14 days before the next menstrual period, and the normal menstrual cycle is 28-30 days. If a woman usually has a 30-day period, and if she has her period on the 20th, ovulation is 14 days before her next period, which is the 6th. Due to individual differences, ovulation may be early or delayed. For women with irregular menstrual cycles, ovulation is also irregular and can be determined by monitoring the basal body temperature and observing the discharge. In addition, women will have a clear white streak during ovulation, which can be determined on its own. For women who want to get pregnant, they can consider having intercourse during ovulation. For women who do not want to get pregnant, they can choose to have intercourse during the safe period, i.e. 1 week before or 1 week after menstruation, but it is recommended to take certain contraceptive measures to prevent unwanted pregnancy.