Ovulation Calendar & Fertility is a very simple, free Android app that aims to give you insight into the times of month you are most likely to become pregnant. By entering the 1st day of your last period, and the length of your cycle, the app makes an estimate of the best times to try to have a baby and, were you to get pregnant, when you could expect your due date to be. When Ovulation Calendar & Fertility has the timing figured out, you can add the special days to your calendar.