The Calendar Method (Rhythm)

This is probably the least effective fertility awareness birth control method. It involves tracking your menstrual cycle and then using past experience to predict future ovulations.

You need to chart your menstrual cycle for at least eight months (but preferably for a whole year) before you begin using this method. When you are charting your period, you cannot be on any hormonal birth controls, and so you need to use alternative methods of birth control during this first year.

What you do is you consistently mark the first day of your periods on a calendar. You keep a chart that documents the first day of your period and the number of days in the cycle preceding it. Your chart might look something like this:

First Day of Period	Length of Previous Cycle
March 17	27
April 16	30
May 13	28

Once you have kept this chart for at least eight months, but ideally for a year, then you will be able to roughly chart your fertility using the calendar method.

You cannot use this method if you are inaccurate at keeping records, or if you have irregular periods. Remember that external stressors such as diet, exercise, and emotions affect your menstrual cycle, and mean that this method can be very unreliable.

However, if you are using another fertility awareness method, then you will also be charting your menstrual cycle on a calendar, and this method can help reinforce other styles of contraception.