Basal Body Temperature
Your cycle dictates very small changes in your body's temperature. During the first part of your cycle, estrogen levels rise and cool your body, but during the second half of your cycle—around ovulation and thereafter—the level of progesterone comes up, which heats your body. Tracking your temperature indicates when you are have ovulated, as your temperature will rise and remain at that level until your period. Taking your temperature every morning at approximately the same time over several months will help you tune in to your most fertile days.
What Do I Have to Do?
Take your temperature every morning at the same time. The variances in your temperature are going to be within fractions of a degree, so it’s best to get a basal thermometer that records almost exact temperatures from 96 to 100 degrees. You can take your reading orally, rectally, or vaginally, but it is imperative that you remain consistent in your method. It is also of the utmost importance that you take your reading first thing in the morning: before getting out of bed, talking, eating, etc. Then, plot your temperature on a basal body temperature chart (they usually come with the BBT thermometer kit).