Thyroid Temperature Tracker: Check Your Basal Body Temperature
Thyroid Temperature Test
Your morning temperature is a proxy for your T3 status. Enter this morning's reading and find out what it says about your thyroid:
Written and medically reviewed by Dr. Westin Childs, D.O. Last reviewed: August 28, 2026
How To Use This Test:
#1. Take Your Temperature The Right Way
First thing in the morning, before you get out of bed, before coffee, before moving around. Keep the thermometer on your nightstand so you don’t have to get up for it. Oral is best, and any basic thermometer works.
#2. Enter Your Reading
Type in this morning’s temperature, then tell the test how you took it and where you are in your cycle if you have one. Both change how the number should be read.
#3. Get Your Read
You’ll see where your temperature falls, what it suggests about your T3 status, and anything about your reading that needs a caveat.
#4. Track The Trend
One morning is a clue. The trend is the answer. Save your reading to your free Thyroid Tracker and a few mornings a month draws the real picture.
Why Your Morning Temperature Says So Much About Your Thyroid
Your thyroid is like your body’s thermostat. It sets how much heat your body makes, and T3, the active thyroid hormone, is what does that work at the tissue level.
When your thyroid slows down, it takes your body’s heat along with it.
That’s what makes your morning temperature useful: it’s a free, at-home window into how much thyroid hormone your tissues are actually using. Your labs measure what’s in your blood. Your temperature reflects what your body is doing with it.
And modern data backs up what thyroid patients have noticed for decades: the old 98.6 standard is too high for most people, and a temperature that sits well below the normal range morning after morning means something.[2][3]
To be clear, a thermometer can’t diagnose a thyroid problem, and your labs are what settle it. But if your mornings keep coming in low and you feel cold, tired, and stuck, think thyroid, and get the labs to prove it one way or the other.
What Counts As A Low Thyroid Temperature?
Taken orally, before getting out of bed:
- Under 97.0°F: notably low, and consistent with reduced thyroid activity at the tissue level
- 97.0 to 97.7°F: below the optimal band, the classic low T3 pattern
- 97.8 to 98.6°F: the optimal band
- Over 98.6°F: on the high side, and worth labs if it stays there alongside a fast resting pulse
Two things change how you read your number. Underarm readings come in 0.5 to 1.0 degrees lower than oral, so they need adjusting up. And in the second half of your cycle, after ovulation, your temperature runs 0.4 to 1.0 degrees higher on its own,[4] which is why the test asks where you are in your cycle.
This idea goes back to Dr. Broda Barnes, who proposed the basal temperature test for thyroid function back in 1942.[1] The tool on this page uses the same core idea with modern reference points and the cycle correction his original version didn’t have.
Frequently Asked Questions
It can be. Your thyroid sets your body’s heat production, so a morning temperature that sits low day after day is consistent with low thyroid function at the tissue level. It’s a clue, not a diagnosis. If your mornings keep coming in under 97.8, get your thyroid labs checked and see where they fall.
Between 97.8 and 98.6°F, taken orally before you get out of bed. Most people run lower than the old 98.6 average, and that’s normal. It’s the consistently low mornings, under 97.8 and especially under 97.0, that are worth paying attention to.
It’s based on the same idea. Dr. Broda Barnes proposed in 1942 that your morning temperature reflects your thyroid function, and his protocol used underarm readings for 10 minutes before rising. This version uses oral readings, modern reference points, and a correction for where you are in your cycle, which the original didn’t account for.
Yes. Any basic digital thermometer works. A basal thermometer reads to two decimal places instead of one, which is nice for spotting small trends, but it isn’t required. Here’s my guide to choosing and using one.
Progesterone. After ovulation, rising progesterone lifts your temperature by 0.4 to 1.0 degrees until your period starts. That’s normal, and it’s exactly why this test asks where you are in your cycle: a reading in the second half of your cycle needs to be judged with that shift in mind. If you track fertility by temperature, you already know this curve.
Related Thyroid Tools
Your temperature is one window. These cover the rest:
- Optimal Thyroid Lab Test Calculator: see if your thyroid labs are in the optimal range
- Thyroid Weight Gain Calculator: how many pounds of your weight come from your thyroid
- All Thyroid Calculators & Quizzes: the full set of free tools
Scientific References
- Barnes B. Basal temperature versus basal metabolism. JAMA. 1942;119(14):1072-1074.
- Mackowiak PA, Wasserman SS, Levine MM. A critical appraisal of 98.6°F, the upper limit of the normal body temperature, and other legacies of Carl Reinhold August Wunderlich. JAMA. 1992;268(12):1578-1580.
- Obermeyer Z, Samra JK, Mullainathan S. Individual differences in normal body temperature: longitudinal big data analysis of patient-reported temperatures. BMJ. 2017;359:j5468.
- Baker FC, Driver HS. Circadian rhythms, sleep, and the menstrual cycle. Sleep Med. 2007;8(6):613-622.