you need a basal body thermometer, also called "ovulation thermometer" and can get one at a pharmacy. Fertility friend has an online chart that you can use to record your temps and it also has a good online tutorial to teach you all about charting and stuff. Ovulation is SUPPOSED to be about 14 days before your period, but the problem is that women's luteal phase (the time after you ovulate and before your period) varies greatly from woman to woman. So for a "normal" 28 day cycle, you "should" O on day 14, but if you have a short LP, you may O on day 18, or if you have irregular cycles, it could change from month to month. Your LP will always be about the same length, but the time before you ovulate can change from month to month in women with irregular cycles. That's why it's a good idea to temp/chart so that you get a clear picture of when you normally O, so you can time BD properly. I'm sure there will be a "sticky" somewhere in the forus that goes into this in more detail, or you could also do a search through the articls on the main BellyBelly site for more info.