Calendar (Rhythm) Method

This is also known as "Natural Family Planning". This method is based on the assumption that ovulation occurs 14 days +/- 2 days before the start of next menstrual period, and that sperm are viable for 48-72 hours and ovum (eggs) for 24 hours.

The woman must record her menstrual cycles for 6-8 months so that the shortest and longest cycles can be determined. The first day of menstruation is the first day of the cycle, the fertile phase is calculated from 18 days before the end of the shortest cycle through 11 days from the end of the longest cycle. For example, cycle ranges from 24-28 days then the fertile phase is from day 6-17. To be effective couples must abstain during the fertile phase. This is the least reliable fertility awareness method.

Natural Family Planning