A woman practices the rhythm (calendar) method of birth control by learning to recognize the days she is fertile and not having sex before and during those days. The rhythm method does not work for all couples. Women who have regular menstrual cycles and who are very careful about when they have sex usually find it to be effective. Women who have irregular cycles and who are not so careful often end up becoming pregnant.

The failure rate usually estimated as 25%.

Advantages:

• low cost
• safety
• no need for medical devices or medications
• lack of side effects

Disadvantages:

• the fact that both members of the couple must be involved in the process
• the need to abstain from sex during your fertile days, or to use backup contraception
• the need to consistently track your cycles for at least six months before the method can be considered reliable
• a high failure rate compared with almost all other non-abstinence-based birth control methods (i.e. condoms, the pill, diaphragms, etc.)