With Calendar-based methods, pregnancy is prevented by monitoring the days of a woman’s menstrual cycle to determine the beginning and end of her fertile period. Examples of these methods include the Standard Days Method and Calendar Rhythm Method.

In this method, a woman monitors the days in her menstrual cycle, counting the first day of monthly bleeding as day 1. Unprotected sex is avoided through days 8-19 as these are considered fertile days. Safe period for intercourse are days one (1) through seven (7) and from day 20 to when the next monthly bleeding begins.

In this method the first day of monthly bleeding is counted as day one (1).A woman can determine the first day of her fertile time by subtracting 18 from the length of her shortest recorded menstrual cycle. Then 11 days is subtracted from the length of time of her longest recorded cycle. This determines her fertile period. Unprotected sex should not be practiced or a diaphragm or condom should be used. These calculations are updated every month using the six (6) most recent cycles.