For NFP to be effective in avoiding pregnancy, it is best if you are taught by a specialist NFP teacher. Both you and your partner must follow the guidelines very carefully, avoiding intercourse during the fertile time. NFP is most effective when women record more than one fertility indicator. This means that 2 women in 100 will get pregnant in a year. If NFP methods are not used according to instructions, more women will get pregnant.
Some couples choose to combine their fertility awareness with a barrier method such as a condom.
The effectiveness of combining methods depends on how well the barrier method is used. You can use fertility awareness to plan a pregnancy as well as to avoid a pregnancy. You do not use any chemical agents or physical devices. There are no physical side-effects. It is effective if you are taught well and you follow the instructions.