What is a basal body temperature? (BMT). “Basal” means, “base,” and your basal temperature is your body temperature taken the very first thing in the morning before you’ve gotten out of bed. Once you get out of bed, the movement of your muscles heats up your body, so it’s essential that you do the test before you get out of bed; have anything to eat or drink; or engage in any activity. This will measure your lowest temperature of the day, which correlates with thyroid gland function. Patients concerned about issues like hypothyroidism, weight loss, etc should complete a BMT.

The BMT Test is a direct measure of thyroid function. Thyroid hormone is the master regulator of metabolism, so like a thermostat, the lower you turn it, the lower the temperature. Dr. Broda Barnes, an eminent thyroid researcher pointed out that thyroid hormone influences every cell in the body from inside the cell, whereas lab tests only measure blood levels of hormone outside the cell. To be sure, lab tests are extremely valuable, but they do not directly measure thyroid function. More information on the BMT Test can be found in books by two leading authorities in treating thyroid problems; Dr. David Brownstein’s Overcoming Thyroid Disorders and Dr. Mark Starr’s Hypothyroidism Type 2.


1.) If using a Mercury Thermometer, shake it down to 96 degrees or less before going to bed. In the morning, as soon as you wake up, put the thermometer deep in your armpit for 10 minutes and record the temperature. Lie back and relax, keeping your armpit closed over the thermometer. If using a Basal Digital Thermometer, in the morning, as soon as you wake up, place it under your armpit until it beeps.

2.) The normal basal temperature averages 97.8-98.2 degrees F. The lower your BMT, the more likely you are to have a functionally low thyroid. The temperature should be taken for five days.

3.) For pre-menopausal women, the temperature should be taken starting the second day of menstruation. That is because considerable temperature rise may occur around the time of ovulation and give incorrect results.

4.) Do not perform the test when you have an infection or any other condition which would raise your temperature.

5.) Do not use an electric blanket as it will artificially increase your body temperature.

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Want to learn more about thyroid function and conditions like hypothyroidism? Visit our page where Dr. Douglas Weed discusses thyroid physiology.


About the Author: Dr. Douglas L. Weed

Dr. Weed practices Functional Nutrition, Chiropractic care, and offers weight loss solutions in Napa, CA at Heun Chiropractic, Inc. He has a doctorate in Chiropractic care and he has received certifications in physical rehabilitation and as a Qualified Medical Examiner. With a post-graduate certification in Functional Medicine, focusing on functional endocrinology, digestive disorders and Peripheral Neuropathy, he is committed to lifelong education and helping patience transform their health.