The TwoDay Method® is a fertility awareness-based method of family planning. It was developed by the Institute for Reproductive Health at Georgetown University and tested in a multi-site efficacy trial with nearly 500 women. It is designed to be simple, accurate and effective for women with cycles of any length. In an efficacy trial, the TwoDay Method was found to be more than 96% effective with correct use and 86% effective in typical use. This means that when used correctly, fewer than 4 out of 100 women became pregnant in a year while using this family planning method. When users had unprotected intercourse during potentially fertile days despite using the method to avoid pregnancy, 14 out of 100 women became pregnant.
Read the original research article here: Efficacy of the new Two Day Method of family planning.