Here are some facts cited in the report about girls’ first periods: Typically start two to two-and-a-half years after breast development begins. Generally last two to seven days. Menstrual cycles range from 21 to 45 days. Charting periods can help uncover any menstrual changes or problems.

A menstrual cycle lasts from the first day of a girl’s period until the first day of her next period.

FOXNews.com