Basal Body Temperature


Your metabolic rate, which is how much energy you burn, is largely determined by your thyroid gland. Your body temperature is also largely regulated by your thyroid gland, and a low body temperature can be an indication of slow metabolism and low thyroid. Reduced thyroid function often manifests as a drop in basal body temperature to below the normal level of 98.6 degrees F. Use an accurate thermometer and write down your results for three days.


  1. Place the thermometer beside your bed before you go to sleep. If you're using a mercury thermometer, shake it down to below 95° F.
  2. On waking, before doing anything else (including talking), place the thermometer in your armpit for a full 10 minutes. Stay as still and relaxed as possible. If it helps, use a kitchen timer.
  3. After 10 minutes, read and record the date and temperature. Women may also want to record where they are in their menstrual cycle.
  4. Menstruating women should perform the test on days 1, 2 and 3 of their cycle, which are the first three days of menstruation. If menstrual cycles are irregular, make an educated guess about when your period should be starting.
  5. Men, children, and postmenopausal women can perform the test at any time.
  6. Women using oral or topical progesterone should not take progesterone the day before or on the days that the basal temperatures are taken.

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