Most people are between 28 and 35 days, but there are also a few people 1 whose cycle is as short as 20 days and as long as 45 days. Within the above range, as long as menstruation is regular, it is normal.
Menstrual period: The period of vaginal bleeding is called menstrual period. Most people's menstrual period lasts for 3 ~ 5 days, but as little as 1 ~ 2 days and as many as 7 ~ 8 days are within the normal range.