Check out my monthly cycles.com It has free charting of your periods and ovulation. This chart will show you which day your ovulation is and how many days before and after you could get pregnant. I think it even tells you which days of your cylce a girl is more likely. From what I have read you would want to have sex a few days before ovulation to increase the chance of a girl. Something to do with how the x chromosome swim. They are slower and more likely to just be getting to the egg if you have sex a few days before. The y sperm are just in a hurry so if you have sex on the day of ovulation they are mote likely to get to the egg first and then you get a boy.
Your cycle doesn't calculate wether you are going to have a girl or a boy. It's determined by the mans sperm. The sperm are male and female. The female sperm are much faster than the male sperm, so your odds are good there. :) It's the boys sperm that are sluggish. I know my information is accurate, I get it from A Child Is Born, by Lennart Nilson, and my doctor told me this as well.