How to use a Basal Body Thermometer

Basal body thermometers are a special thermometers used to read your waking temperature—your basal body temperature (BBT).  After a long period of rest your body temperature is at its lowest of the day which is the best time of day to get an accurate basal body reading.

Your thermometer will come with a kit so that you can track your temperature readings to learn your body’s fertility patterns.  You also have space on the recording graph to notate any of the PMS symptoms you may be experiencing.

What is a Basal Body Thermometer?

What makes the a basal body thermometer different from a standard thermometer is that it is ultra-sensitive to give you the most accurate temperature readings. We currently stock two types of Basal Body Thermometers – a standard one which is the ideal choice to start out with and a clinical grade one which is the one we recommend for regular use.We generally recommend charting in Fahrenheit as it makes the temperature changes easier to see.

Basal Body Thermometers are primarily used to track ovulation and fertility. They are designed to measure the subtle temperature changes that occur in a woman’s body during different phases of her menstrual cycle. By tracking these changes, women can identify their most fertile days and plan or prevent pregnancy accordingly. It is recommended to take the temperature at the same time every morning before getting out of bed for the most accurate results. Basal Body Thermometers are also a useful tool for diagnosing fertility issues or other health problems that may affect a woman’s reproductive system.

Recording your Basal Body Temperature (BBT)

The calendar graph that comes in your kit allows you to record each day of your menstrual cycle by filling in the date and the day of the week horizontally across the top.  Vertically under each day you will record your precise temperature in Fahrenheit or Celsius depending on your countries standards of measurement.

Our FREE BBT chart can be downloaded here:
BBT Chart – Zoom Baby – FAHRENEHEIT

It is a good idea to keep your thermometer and chart on the bedside table, next to your bed.  This is because you will need to record your temperature first thing in the morning—before you get out of bed.  It is also very important for you to take your temperature at the same time every day.

After you have done three menstrual cycles with your Basal Body Thermometer you should be able to detect a pattern.  After you ovulate your body temperature rises .36-.9 degrees F or .2-.5 degrees C.  The goal of tracking your basal body temperature is to assist you in planning future intercourse and to learn your fertility patterns.

In addition to tracking your basal body temperature, it is also helpful to monitor other signs of fertility such as cervical mucus, changes in cervix position and texture, and ovulation pain. By combining these methods of fertility tracking, you can get a more comprehensive understanding of your menstrual cycle and increase your chances of conceiving if that is your goal.

It is important to note, however, that tracking basal body temperature and other fertility signs are not foolproof methods of contraception. It is still possible to become pregnant even during periods of low fertility, and it is always a good idea to consult with a healthcare provider about the best form of birth control for your individual needs.

Overall, tracking your basal body temperature is a simple yet effective way to gain insight into your menstrual cycle and fertility patterns. By being consistent with taking your temperature at the same time every day and recording your results, you can better plan for pregnancy or other aspects of your reproductive health.


If you want to know ahead of time when you are ovulating, then you would be better of using a different method of ovulation detection, such as Ovulation Test Kits or a Fertility Monitor.

How To Start Tracking Your Monthly Cycle

Charting your temperature accurately will make it easier for you to determine when pregnancy has occurred.  Accurate charting has also been linked to timing your intercourse in response to fertility signs to help choose the gender of your baby.

To begin tracking you want to start taking readings on the first day of your period.  Make sure you begin on the day that you have a steady flow, not days in which you are simply spotting.  Keep these key points in mind while tracking:

  • You must use a basal body thermometer not a regular thermometer.
  • Notate the exact start date of your cycle on your chart.
  • Do not eat or drink prior to taking your basal body temperature.
  • Your temperature must be taken first thing in the morning before you are physically active, otherwise you will not have an accurate reading.  Keep the thermometer under your tongue for a minimum of 2-3 minutes.
  • Use a dot, as opposed to an X or a checkmark, this will allow for a cleaner and easier to ready chart.
  • Document your PMS symptoms in the space provided to increase your odds of detecting patterns.
  • Also record any other changes to your body like headache, fever, or illness.
  • Start a new chart when you begin your next menstrual cycle.

Photo by Anthony Cunningham for Zoom Baby

This post first appeared in 2018. It was last updated in June 2023.

Zoom Baby is a leading supplier of Pregnancy Tests and Ovulation Test Kits

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