It also prepares your body for pregnancy each month. A cycle is counted from the first day of 1 period to the first day of the next period. The average menstrual cycle is 28 days long. Cycles can range anywhere from 21 to 35 days in adults and from 21 to 45 days in young teens.
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Technically menstrual cycle and how long it last differs to everyone.
maybe the person, has irregular so approximately her menstruation may last up to one month for those regular, her menstruation may just be for a week or two.