Since NFP methods are not contraception, their effectiveness works both ways—for achieving and postponing pregnancy.
This is important news to married couple because typically "effectiveness" is thought to be "only" related to avoiding pregnancy. In NFP education, both husband and wife learn about their combined fertility and are taught how to live in harmony with God's design. They are also encouraged to discern whether God is calling them to attempt to have a child or to postpone a pregnancy. The methods of NFP are the only approach to true responsible parenthood because they respect God's design for married love!
When couples wish to attempt pregnancy they can time sexual intercourse to the fertile window of the menstrual cycle, thereby optimizing the possibility of becoming pregnant.
When wishing to avoid pregnancy, studies show that couples who follow their NFP method’s guidelines correctly, and all the time, achieve effectiveness rates of 97-99%.
Others, who are unclear about their family planning intention (i.e., spacing or limiting pregnancy) or are less motivated, will not consistently follow the method’s guidelines and have a lower effectiveness rate of 80-90%.