Natural Cycles offers a contraceptive app, spearheading digital contraception, a new category in female reproductive health. Users measure their basal body temperature in the morning and the app computes the temperature (and other relevant data like levels of luteinizing hormone) through an algorithm to calculate whether they are fertile or not. Natural Cycles’ subscription product relies on an algorithmic method to predict which days women are fertile during their monthly cycle — with an in-app color-coded calendar informing users if they could have unprotected sex on a given day or not. Women using the app are required to measure and input their body temperature daily using a basal thermometer. Natural Cycles relies on this and other individual data inputs to algorithmically calculate the probability of the user being fertile on each day in her cycle.