Your most fertile days are when you are ovulating which is usually 12-14 days BEFORE your NEXT period. That time period is called your luteal phase, the time between ovulation and your period. You are fertile most around ovulation, so you want to have sex around the day that you are ovulating.

Go to fertilityfriend.com and sign up for free. You can keep track of your periods and after a cycle or two, it can give you a rough estimate of when you are going to ovulate.