Question: what is the first day of menstruation?
Answer: The first day of menstrual bleeding is considered Day 1 of the cycle. Your period can last anywhere from 3 to 8 days, but 5 days is average. Bleeding is usually heaviest on the first 2 days. Once the bleeding stops, the uterine lining (also called the endometrium) begins to prepare for the possibility of a pregnancy.