Find Your Most Fertile Days: A Guide to Tracking Your Fertility

So how do you track your BBT? The first step is to buy a digital BBT thermometer from a drugstore. Most large drugstores carry these, or they can be ordered by a pharmacist. The rest is simple. "This is the easiest sign to track," says Wodzinski. "You just wake up, take your temperature with a digital BBT thermometer every day, and write it down on a chart."

It's important to remember two things about taking the BBT. First, you need to take your temperature at around the same time each day with the same thermometer. Second, it must be the very first thing you do upon waking--no going to the bathroom, reading, having sex, eating, or moving around before taking your temperature.

The BBT sign alone can help you predict your fertile time after you have charted one or two cycles. You may begin to notice that your temperature shift happens at about the same day during each cycle--say 14 or 20 days after the first day of your period. You can then estimate the day of ovulation in your next cycle and time intercourse accordingly. However, the BBT sign is much more effective in combination with the other fertility sign: cervical fluid.