A woman's menstrual cycle generally lasts 28 days, but some women may have a different menstrual cycle. If menstruation begins on the 9th, the cycle is generally 28 days. Counting from the 9th, a woman's menstrual cycle is 28 days, so the date of the next menstrual cycle is February 18th.

In a woman's menstrual cycle, the dangerous period refers to the period between two menstrual periods in a woman's menstrual cycle. If a woman does not take any contraceptive measures during the risk period, she may become pregnant.

The specific dates of dangerous periods in a woman's menstrual cycle vary from individual to individual. Generally speaking, the dangerous period starts 14 days before the next menstruation and lasts for 1-2 days. Therefore, if a woman’s next menstrual period is February 18th, the dates of the dangerous period are February 13th and February 20th.

If a woman wants to become pregnant, it is recommended to take contraceptive measures to avoid pregnancy. If a woman does not want to become pregnant, it is recommended to follow the safe period calculator or the advice of a professional doctor to ensure that she does not become pregnant.