- The calendar birth control method, also known as the rhythm method, tracks the days of your menstrual cycle in order to predict fertile times, ovulation and "safe days," or days during which intercourse is least likely to result in pregnancy. This is a traditional technique that remains popular with conservative Catholics as well as women who prefer not to use hormonal birth control or other forms of contraception. One of the main determinants of success with calendar birth control is having a regular menstrual cycle. If your cycle is highly variable, meaning it does not last the same amount of time from month to month, the calendar method alone may not be as accurate as combination with other approaches. These include tracking basal body temperature, or BBT, and regularly checking your cervical mucous consistency.
- The calendar method predicts ovulation by subtracting 14 days from the length of your average menstrual cycle. For instance, if your cycle always lasts 30 days, then your predicted ovulation day is 16 days after your period begins. A woman's most fertile days usually last from a few days before to a few days after she ovulates. In a 30-day cycle, your most fertile times would range from day 12 to day 20. Therefore, days 1-11 and 21-30 would be considered your "safe days." If your cycle length fluctuates, your ranges will fluctuate as well. It is best to track your safe days based on the shortest and longest cycles you typically have if you wish to avoid pregnancy.
- According to the Mayo Clinic, calendar birth control is about 87 percent effective in preventing pregnancy when used accurately. As a comparison, condoms are about 85 percent effective. Birth control pills take the lead at 92 percent. One of the key factors in using the calendar method successfully is practice. Most health care providers suggest that you do not solely rely on this method unless you have tracked your cycle over the course of 4 to 6 months and have become familiar enough with it to accurately predict ovulation and the start of your menstrual flow. Even a 1 to 2 day fluctuation in the length of your cycle can mean the difference between a safe day and a fertile day. Cycle length can change over time, or even if you are undergoing a stressful time. If you are use this method alone, track diligently and adjust as needed for any variations. However, if you want to avoid becoming pregnant, the calendar method is most effective when combined with other forms of birth control, such as a condom or diaphragm.
