Effectiveness rates for natural family planning range from 75% (typical use) to 99% (perfect use). The majority of failures with this method are due to couples engaging in intercourse too close to ovulation. In addition, a woman may ovulate earlier or later than usual because of diet, stress, or alcohol use. This method is best suited for those needing to space pregnancies, rather than for those who want to avoid pregnancy.
Natural family planning is an acceptable form of birth control for those who cannot use another method for religious reasons. It is also inexpensive, teaches couples about the menstrual cycle, may encourage couples to communicate more about contraception, can involve the male, and has no medical side effects. It also helps women if they eventually want to get pregnant, because they know when they ovulate. Couples who use natural family planning use a variety of sexual expressions when they cannot engage in vaginal intercourse.