How effective is the calendar method of contraception in preventing pregnancy?

The calendar method of contraception, also known as fertility awareness or natural family planning, is not as effective as other forms of Birth Control. It relies on tracking a woman's menstrual cycle to determine when she is most fertile and avoiding intercourse during that time. However, this method is not foolproof and has a higher failure rate compared to other contraceptive methods. It is important to use additional protection if relying solely on the calendar method to prevent pregnancy.