How to Track Your Basal Body Temperature & Why It’s Important

Tracking your basal body temperature (BBT) is one of the easiest things you can do to track your cycle, fertility, and metabolic health. It’s simple and relatively free once you purchase a thermometer. Your basal body temperature is your temperature first thing in the morning upon waking when you are fully at rest. Getting out of bed and taking even a few steps to the bathroom can effect your resting basal body temp. It is best to use a specific basal body temperature thermometer because it measures to two decimal points allowing you to track even subtle changes in temperatures. You can find basal body specific thermometers for under $10. This is the one I use.

Your BBT provides insight into your cycle and fertility as well as your metabolic health. Tracking your morning temps can help you determine if, and when, you’ve ovulated in your cycle. Ovulation may cause a slight increase of 0.5 - 1°F in your basal body temp as a result of rising progesterone levels. Your basal temp may remain elevated for a few days or up to a week after ovulation. If your temps remain high for at least 3 days, you can assume you’ve ovulated. Tracking your temps for a few months or cycles can help you track any patterns and notice any changes.

Tracking BBT is a method that can be used to determine fertility and a form of natural birth control. You are most fertile in the few days prior to ovulation. Now you might be thinking, if I am most fertile and likely to get pregnant before I notice a change in my temperature, how is that a reliable form of birth control? That is a great question and why it really takes a consistent effort in tracking your temps and knowing your cycle.

An average cycle length is 28 - 29 days, with some variance. Ovulation typically happens around day 14 in a typical 28 day cycle. Keep in mind that since you are most fertile the few days prior to ovulation. If you are trying to conceive, this would be a great time to engage in unprotected sex. If you are not trying to conceive, you may consider avoiding sex or choosing to have protected sex around this time.

To track your basal body temperature:

• Get a basal body thermometer or any thermometer that measures to two decimal places.

• Take your temperature first thing upon waking before you even get out of bed. It is best to take your temperature at a consistent time each day. I recommend keeping the thermometer in your mouth for 3-5 minutes before you actually take your temperature so that you can ensure the thermometer is warmed up and giving you the most accurate reading.

• Record your temperature in a calendar, app, notebook, or however works best for you. This step is critical as it will allow you to identify a temp increase, track patterns, and notice any changes.

• Consider your fertile window and when to engage in unprotected sex or not depending on your family planning status. You are most likely to get pregnant 4 days prior to ovulation and the day after ovulation if you engage in unprotected sex.

On average, most people will have a basal body temperature around 96 to 98°F prior to ovulation. After ovulation you may notice a rise in your basal temperature with temperatures of 97-99°F. How much your temperature rises is different for everyone, which is why tracking your temperatures consistently is so important.

You can also use your basal body temperature to track pregnancy. If you notice your temperature stays elevated and doesn’t drop before you would normally get your period and you don’t get your period, you should take a pregnancy test or see a healthcare provider to check if you are pregnant. Progesterone is the key pregnancy hormone. Progesterone levels continue to rise after conception to support pregnancy by thickening your uterine lining. Progesterone tends to lead to warmer body temperatures which is why you see your temperature remain elevated if an egg is fertilized by a sperm and conception occurs.

Body Temperature and Metabolic Health

Your basal body temperature provides a lot of insight into your health outside of your cycle and fertility. Your body temperature is linked to your thyroid and metabolic health. While it is not a definitive marker, it can be used in combination with symptoms to determine how your thyroid is functioning.

Metabolism is the chemical process that occurs when your body converts the foods you consume into energy. This energy fuels other functions in the body including breathing, blood circulation, digestion, regulating body temperature, regulating hormone levels, and so much more.

Your metabolism is controlled by your thyroid. Your thyroid hormones activate genes that increase metabolic rate and thermogenesis. Since your thyroid regulates your metabolism and your metabolism regulates body temperature, you can see how tracking your basal body temp can provide insight into your thyroid function. If your temps are low, it may be due to a sluggish thyroid. On the contrary, if your temps are high, it may be due to an overactive thyroid.

In regards to fertility, you want a happily functioning thyroid. Thyroid hormones impact ovulation which impacts progesterone levels which is needed to support pregnancy.

The information provided in this post is informational and does not replace direct medical care with a licensed and trained medical provider. If you are concerned or have questions about your thyroid function, fertility, or anything else, please reach out to your medical provider.

References:

professional, C. C. medical. (n.d.-a). Basal body temperature: Family planning method. Cleveland Clinic. https://my.clevelandclinic.org/health/articles/21065-basal-body-temperature

professional, C. C. medical. (n.d.). Metabolism: What it is, how it works and disorders. Cleveland Clinic. https://my.clevelandclinic.org/health/body/21893-metabolism

Shahid, M. A., Ashraf, M. A., & Sharma, S. (2023, June 5). Physiology, thyroid hormone. StatPearls [Internet]. https://www.ncbi.nlm.nih.gov/books/NBK500006/#:~:text=In%20general%2C%20when%20the%20thyroid,increased%20oxygen%20and%20energy%20consumption.&text=Thyroid%20hormones%20have%20a%20permissive%20effect%20on%20catecholamines.