A 30-day menstrual cycle with a period on the 11th and intercourse on the 20th may result in pregnancy, but the chances are not high, but the accuracy of this calculation is limited. If you calculate according to the normal menstrual cycle, after the period on the 11th, the chances of pregnancy on the 20th are not high. However, some special circumstances cannot be excluded, so it is recommended that women who do not have a pregnancy plan should take the contraceptive pill as prescribed by their doctor in a timely manner to avoid unplanned pregnancy. If you want to achieve effective contraception, you can take oral short-acting contraceptive pills, use condoms and so on, are all optional and reliable means of contraception. Safe period contraception is not absolutely safe, so do not be careless when having sex, you need to do a good job of contraception throughout. If there is any discomfort, it is recommended to consult a doctor as soon as possible. If there is no need to prepare for pregnancy, it is recommended to take contraceptive measures.