UPDATE A thorough study of more than 95 fertility awareness tracing apps sets the record straight on what these apps can and cannot do. In short, rely on your teacher and use the apps a tool to help.
Clue- Period & Ovulation Tracker (Free) iOS Some reports bill this as a Natural Family Planning App. But it is very clear in the developer’s presentation that this is not to be used to prevent pregnancy. Still, it is a tool to help track your menstrual cycle to predict your next period or bout with PMS. Fertility days are highlighted for you. According to developers, Clue uses an algorithm to calculate and predict your own unique cycle. And, developers claim, “the more you use Clue, the more accurate it gets.” Check out their video which explains how this app works and the educational material it offers.