Menstrual Calendar is based on real scientific researches. It helps you determine your fertile days of the month, so you can either achieve or avoid pregnancy. * HOW TO USE *To generate your ovulation calendar you should provide the following details:- Date of the last period (on the calendar on the main tab).- Average length of the periods (on Settings tab).- Length of the Luteal Phase (on Settings tab or use default value).The application works best for women with regular menstrual cycles, the average cycle length is also a valid way to predict when the ovulation should happen.