*** Menstrual Calendar, the Best App to calculate your Menstrual Cycle *** Menstrual Calendar is a free application that provides information about each woman's menstrual cycles (fertile days, ovulation and period) to help her monthly monitoring using the Ogino-Knaus method in order to achieve or avoid pregnancy. Calculations and criteria used by the application to set the cycles are the ones made by the Princeton University, in the United States. According to different studies, the effectiven