The menstrual cycle is usually calculated from the first day of the last menstrual period to the first day of the next menstrual period.
A normal menstrual cycle starts from the first day of vaginal bleeding and ends on the first day of the next menstrual period, which is 28 days on average. Normally, during this period, it is normal for menstruation to be one week earlier or later, so the normal menstrual cycle is usually between 21 and 35 days.
Menstruation is a normal physiological phenomenon for women, but it is also affected by many factors, so women’s periods may fluctuate. If there are obvious abnormalities in menstruation, it is recommended to consult a doctor in a timely manner, under the guidance of a professional doctor for targeted treatment.