How to accurately calculate a woman’s menstrual period? A woman\’s menstrual cycle often changes due to many factors, but if you\’re trying to conceive, understanding your cycle is crucial to conceiving. To help you prepare for scientific pregnancy preparations, here is some useful knowledge on how to accurately calculate a woman’s menstrual period. Mastering basic physiological knowledge and understanding your own menstrual cycle and ovulation time in your body is the key to accurately calculating your menstrual period. Generally speaking, the menstrual cycle starts from the first day of a woman\’s pregnancy and ends on the day before the next pregnancy. The length of the menstrual cycle usually ranges from 21 to 35 days