People choose to avoid pregnancy naturally for many reasons. Some have religious beliefs that discourage the use of contraception. Some prefer to avoid contraceptive products that contain hormones. Natural family planning is inexpensive, has no undesirable side-effects and doesn’t require any prescriptions or visits to a health care provider. It offers many benefits, but it's not as effective as several other methods of avoiding pregnancy. Talk to your health care provider about the best method of avoiding pregnancy for you.
Track your menstrual cycle on a calendar. The first day of your menstrual period is considered “day one.” The American Pregnancy Association recommends tracking your cycle for at least eight months in order to accurately determine your fertility period because the length of your cycle varies slightly from month to month. If your menstrual cycle is not regular, natural family planning might not be a good method of contraception for you.
Determine which cycle was the shortest and which was the longest. You’ll use that information to determine your fertile period, which is the period during which you must avoid having sexual intercourse in order to avoid pregnancy.
Subtract 18 days from the length of your shortest cycle to determine the first day of your fertility period. For example, if your shortest cycle was 28 days long, then subtract 18 from 28. You get 10, meaning day 10 is the first day of your fertility period. Remember, do not have unprotected sexual intercourse during your fertility period.
Subtract 11 days from the length of your longest cycle to determine the last day of your fertility period. For example, if your longest cycle was 31 days, then subtract 11 from 31. You get 20, meaning day 20 is the last day of your fertility period. After that, you can have unprotected sexual intercourse without the likelihood of getting pregnant until the first day of your next fertility period.