The average length of a period is 3-7days. The length of time between periods can be anywhere from 21-35 days. It's a good idea to get to know your cycle right from the start. On your calendar each month, circle or shade in the days that you menstruate. As your cycle evens out, you'll begin to see a regular pattern on your calendar. Then you can see when your next period will probably start by figuring out the average number of days in between your periods. Consult your doctor if your period is very irregular.
Attribution: P&G/Always