You cannot fall pregnant unless you are ovulating. If your menstrual cycle is regular, then you are almost certainly ovulating regularly. The length of your menstrual cycle will determine when you are likely to ovulate.

To use the ovulation calendar, enter the first day of your last menstrual period and then the numbers of days of your cycle. Before trying to fall pregnant, keep a detailed diary of when your periods fall to determine the length of your cycle. This calendar will act as a guide. There are no guarantees that you will definitely ovulate between the days given, or that, if you do, you will necessarily fall pregnant in that particular cycle.

first day of last menstrual period: day: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 30 27 28 29 30 31    month: January February March April May June July August September October November December    year: 2009 2010 2011 2012 days in menstrual cycle: 20 21 22 23 24 25 30 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50