On the first day of your next
period, mark it on your
calendar, just a little number 1, on the day it starts...and put a 2 on the next day and 3 on the third day and so on and so on, keep on counting the days on the calendar until your period starts AGAIN...on that day start over at number one and voila, you know how long your cycle is...if you mark 28 days on the calendar before you start another period, it's a 28 day cycle...