Basal Body Temperature (BBT) Charting

Basal Body Temperature ChartingIf you desire to understand your menstrual cycle better, basal body temperature charting just might be for you! Your basal body temperature (BBT) is the temperature at which your body rests, which tends to be a bit lower than your “normal” temperature, usually 97 point something degrees F versus 98.6 degrees F. By taking your BBT each morning throughout your cycle you will be able to detect the natural rise in your basal body temperature that occurs just after ovulation. This increase in your BBT is due to the hormone progesterone, sometimes referred to as the “warming hormone”. Once ovulation has occurred, your body begins to produce increasing amounts of progesterone, thereby causing your body to warm up, which is reflected in an increase in your BBT.  (Basal body temperature can be measured using a special thermometer known as a basal thermometer.)

If you are trying-to-conceive (or trying to avoid pregnancy, for that matter), basal body temperature charting can provide valuable information about your menstrual cycle and your fertility status. Charting basal body temperature will help you to identify the exact day that you ovulated, which will help you time intercourse appropriately in future cycles. As you chart your BBT daily, you will notice your chart will become “biphasic”, meaning that it will show relatively low temperatures before ovulation and slightly higher temperatures after ovulation, revealing two distinct phases in your graph. It is important to note that you might see rapid rise in your BBT, or you might see an incremental rise, or it may even rise and fall slightly over several days. Due to this variability, it is important to chart for several cycles to understand the specific way in which you experience this BBT shift. Once you know the cycle date upon which you usually ovulate, you can then predict your fertile window for the next cycle and, therefore, plan your “baby dancing” appropriately.

Charting basal body temperature is really quite easy.  With the use of a special basal body thermometer that can display your temperature in tenths of degrees, you will be able to detect the subtle shift in your BBT (typically only about .4 degrees F) that occurs approximately 24 hours after ovulation. When you are ready to purchase your thermometer, be sure to check out the digital basal thermometers available at The following tips will help you be successful in charting your basal body temperature:

  • Using your digital basal thermometer, take your temperature (typically done orally, although some women prefer to take vaginal or rectal temps) first thing in the morning after sleeping for at least 3 hours, and before you get out of bed.  It is important that you move as little as possible before taking your temperature, as even slight movement can cause your BBT to rise.  For convenience, it is usually best to store your thermometer near your bedside so that you don’t have to move much to reach it. If you use a glass thermometer, make sure you shake it down before going to bed.
  • Remember to take your BBT at as close to the same time each day as possible, trying to stay within a half-hour window.  Some women find it helpful to set an alarm so they don’t oversleep and miss their BBT window.  Keep in mind that consistency is vital to successful BBT charting, but nobody is perfect! If you happen to oversleep, or miss a day, don’t worry! Unless you miss several days in a row, you will still be able to identify the BBT shift.
  • Record your temperature on a graph (usually provided with the basal body thermometer) daily so that you can easily observe changes in your temperatures on the graph. To pinpoint the date of ovulation, you will be watching for a temperature shift of approximately .4 degrees F over a 48-hour period.
  • If you are not able to detect a shift in BBT in the course of a cycle, it is mostly likely due to inconsistencies in the timing and method of taking your temperature, or perhaps due to an error in charting.  If, however, you move through several cycles without seeing a BBT shift, it is possible that you are not ovulating, and you should consult your physician.

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