Ovy’s algorithm is based on the scientifically recognized symptomthermal method (NFP). There is no need to know the rules by heart as Ovy does the maths for you. The most important data for the calculation of your fertile window and day of ovulation is your basal body temperature and your cervical mucus or alternatively the position of your cervix. Other body signals help Ovy to get to know your menstrual cycle better. Start a new cycle by tracking the first day of your period.