The Effectiveness of NFP
Natural Family Planning has no harmful side effects. It involves knowledge of one’s fertility, and it enriches the mutual respect for the dignity of each spouse. But, does it actually provide reliable information regarding a woman’s fertility on a daily basis, and is it really effective in helping a couple to plan or postpone a pregnancy?
Effectiveness is a percentage normally derived from studies that have determined surprise pregnancy rates. A surprise pregnancy rate is measured in terms of the number of couples out of 100 who become pregnant using a method for one year. Therefore, a surprise pregnancy rate of 15% or 0.15 means 15 couples out of 100 would potentially conceive during one year of using that particular method of birth control. Therefore, a 99% effective rule or method like NFP means that 99 couples out of 100 would potentially not conceive during one year of using that particular method of birth control.
Method & user effectiveness
2007 German study
Comparative effectiveness of birth control methods