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What is a Basal Body Thermometer and Why Should You Care?

What is a basal body thermometer and why should you care?

December 09, 2021

What is a basal body thermometer and why should you care?

Written by Nathalie Daudet

Every single month, naturally cycling women experience a wide range of hormonal events with ovulation being the peak of menstrual cycle hormonal activity. Many women are unaware of the cyclical rise and fall of hormones unless they’re charting their cycle. Using a basal body thermometer is one way of becoming in tune with the hormonal events that happen every month, by letting you peek through a window into your body’s inner rhythms.

What is Basal Body Temperature?

Your body’s lowest body temperature attained during rest is called your basal body temperature (BBT). In the pre-ovulatory phase of your cycle (the follicular phase), your basal body temperature will be within a certain range for you. Once ovulation occurs (in the luteal phase), the presence of progesterone will increase your basal body temperature very slightly - by about 0.2C/0.4F. By tracking BBT every day, you are able to observe this increase in temperature and narrow down the window of ovulation. 

Woman turning off an alarm clock

A basal body thermometer is more sensitive than a fever thermometer, and registers more precisely than a fever thermometer - to the hundredths place. To get an accurate BBT reading with an oral basal body thermometer there are several requirements to ensure a good reading: 

  • Take your temperature at the same time each day, before getting out of bed
  • Ensure you have at least 3 hours of consecutive sleep before taking a reading 
  • You can take an oral temperature under the “pocket” of your tongue
  • You can also take your temperature vaginally, as long as you stick with the same method for your entire cycle

If you have a Tempdrop, you don't have to worry so much about the technicalities of taking your temperature. You put your Tempdrop on, turn it on, and then in the morning take it off and sync it with your phone! If you're sick with a fever, we suggest not wearing your Tempdrop for the night, but it can deal with other things that would otherwise be a disturbance.

What Can Impact a BBT Reading? 

Keep track of factors that may interfere with an accurate reading. You can still track ovulation even with temperatures missing from your chart! If you think you have a temperature that is disturbed, you can exclude just the one temperature.

Here are a list of things that may increase or decrease your temperature. Note: Not everyone may find these things disturb their temperature, so it’s important to take notes so you know which ones impact you!

Woman camping, which can affect basal body temperature readings
  • Drinking alcohol the night before
  • Sleeping in a colder/warmer room than normal, or using a heating pad or extra blanket
  • Sleeping in a different location (on vacation, camping, etc.)
  • Temping significantly earlier or later than your regular time 
  • Time changes or daylight savings time
  • Having a fever
  • Restless sleep, that doesn’t allow you for three consecutive hours of sleep 

There are situations that make it challenging to get an accurate reading, or to wake up at the same time each day. These include working night shifts, having young children, frequent travel, or an inconsistent wake up schedule. For these situations I highly recommend Tempdrop, which will allow you to get an accurate reading even with broken sleep, waking up at different times, variable environmental temperature and more. Tempdrop is worn all night long and excludes outside “noise” that can interfere with a reliable temperature reading. 

What Do I Do With My Temperature Reading?

Basal body temperature chart on Tempdrop app

You can chart your BBT on a charting app or on a paper chart, as long as it allows you to mark on a chart with 0.1 degree increments in Fahrenheit, or 0.05 degrees in Celsius. You may choose to chart in either Fahrenheit or Celsius, and I suggest you choose the one you're most familiar with. No matter your family planning intentions, learning a method of fertility awareness will allow you to interpret your BBT and how it relates to ovulation.

Tempdrop has an amazing app that allows you to manually chart, or you can get a little help interpreting your chart through it.

But Wait, There’s More to Basal Body Thermometers!

BBT is one piece of the charting puzzle. In symptothermal fertility awareness methods, we track BBT and cervical mucus. Tracking BBT will give you a very clear picture of when ovulation has happened after the fact. Pairing it with cervical mucus will give you insights into when ovulation is approaching, which can’t be determined with BBT.

For all family planning intentions, cervical mucus is an important thing to track. Be wary of apps or devices that claim to do the charting for you, especially with basal body temperature alone. It's not an effective way to manage your fertility, as you are missing information prior to ovulation occurring.

If you have any questions about basal body temperature, see if we answered them in our series of Basal Body Temperature: All Your Questions Answered Part I, Part II, and Part III. Still have more questions? Ask on our Instagram!

Buy Tempdrop Now

If you want to dive in deeper to understanding your body and fertility, check out Tempdrop's free Starter Guide to Fertility Awareness! 


Nathalie Daudet

Nathalie Daudet is a social worker and FEMM instructor based in Winnipeg, Canada. She discovered fertility awareness after searching high and low for a non-hormonal method of birth control. After learning the magic of fertility awareness and the gift of body literacy, she decided to pursue formal fertility awareness training and share the knowledge of fertility awareness with women looking for a natural birth control option. Fertility Awareness Project is the hub for Nathalie’s FEMM classes in both group and individual formats, online and in person in Winnipeg. If you love this post and would like to thank Nathalie, shop Tempdrop with Nathalie's unique referral link.

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