The Calendar method is the process of tracking dates of a woman’s menstrual cycle to predict ovulation and peak fertility times based on past cycles. The calendar method may be used to decrease or increase the odds of pregnancy. Due to the natural variation of every woman’s individual cycle, using calendar method alone may not be an effective method of birth control or fertility planning.
The calendar method may also be called standard days method (SDM), rhythm method, or natural family planning.
FertilitySmarts explains Calendar Method
To utilize the calendar method, a woman must track the number of days in her cycle over a period of several months. Calendar method is only effective for women whose cycles run an average of 26-32 days long. Woman with cycles longer or shorter then this time frame would not be able to use the calendar method to determine her fertility window.
With calendar method, the first day of a woman’s cycle coincides with the first day of her period. Days 8 through day 19 are considered fertile days. Women pursuing conception should engage in unprotected intercourse during these days. Women using the calendar method as birth control should refrain from unprotected sex during these days to avoid an unwanted pregnancy.
The remaining days of the cycle, ranging from 1-7 and day 20 until mensuration begins, are considered non-fertile days. Unprotected sex during these days has a very low chance of leading to pregnancy.
Some Fertility Awareness Educators do not consider the calendar method to be a true fertility awareness method (FAM), because it is only predictive in nature and therefore less reliable than the observation of day-to-day changes of fertility signs promoted by other fertility awareness methods.