 This is a prospective, efficacy study of the Dynamic Optimal Timing Dot, an app-based method of family planning that provides the user with information about her daily probability of pregnancy based on the length of her menstrual cycles over time. To use the app, women enter the first day of their menstrual period. Women are then provided information about their daily risk of pregnancy for that day, which they can then use to avoid having unprotected sex. The study is being conducted by the Institute for Reproductive Health IRH at Georgetown University. 