Technology makes it really easy for people to track their cycles online. I like mymonthlycycles.com or TheCarrot.com. You can also track your periods using your iPhone with apps like PMS Buddy. If you're not into digital tracking, just use a paper calendar. Make a dot or symbol on the calendar for each day of your period. After tracking for a few months, you should get a pretty good idea of how long your cycles are, and how many days are in between them.
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