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What Is Basal Body Temperature and Should I Use It to Track My Fertile Window?

04.27.2023 / Clara Siegmund
What Is Basal Body Temperature and Should I Use It to Track My Fertile Window?

Tracking your basal body temperature may help you know if you’ve ovulated, but using this measurement in combination with other fertility tracking methods provides a better picture of your fertile window.

Basal body temperature (BBT) is your body temperature when you’re fully at rest. Many people record their BBT as a way to track their fertility. Essentially, you take your basal body temperature every day to monitor increases that may indicate ovulation. Knowing when you’ve ovulating can help you determine when you’re most fertile, and most likely to get pregnant. 

>>MORE: How Can I Tell If I'm Ovulating? How to Find and Test Your Fertile Window

But does BBT tracking really work to help you get pregnant? The short answer is: yes and no. 

What is basal body temperature?

You may have already heard of fertility awareness-based methods of family planning. These methods, also called natural family planning methods, can be both a form of contraception or a way to achieve pregnancy. Basal body temperature is one of these methods that aims to help you determine when you’re most fertile. A person using fertility awareness-based methods tracks different signs of fertility throughout their menstrual cycle. Factors to monitor include:

  • Your cervical mucus
  • Your basal body temperature 
  • The length of your menstrual cycle

For factors like your cervical mucus and your basal body temperature, hormonal changes throughout your cycle cause detectable physical changes that occur before and after ovulation.  

Take your cervical mucus, for example. Before a developing follicle is released during ovulation, it produces a type of estrogen called estradiol. This hormone facilitates the production of a clear, stretchy cervical mucus that helps sperm travel through the cervix. This cervical mucus is often called “egg white mucus” and generally appears about 3 to 4 days prior to ovulation.

Your BBT is your body temperature when you’re fully at rest. Like with cervical mucus, your basal body temperature is also influenced by hormones. Following ovulation, progesterone is released to prepare the body for a potential pregnancy. This hormone then tells your hypothalamus to increase your body temperature. 

What should my basal body temperature be?

 For most people, body temperature prior to ovulation varies between 96°F and 98°F. If you record a BBT higher than the previous six days for three days in a row, it can be an indication that you’ve ovulated. The rise in temperature is small: for many people, BBT increases around 0.5°F after ovulation. In some people, however, a distinct temperature change may not occur.


How do you track your basal body temperature?

Some people track their BBT to help them determine their fertile window. Your fertile window is the time in your cycle when you’re most likely to get pregnant.

Using the BBT tracking method is relatively simple on paper. Here’s what you need to do:

  1. Get a digital thermometer and make sure it measures temperature to at least one-tenth of a degree (two decimal places). You can’t go wrong if the packaging indicates that the thermometer is intended for measuring basal body temperature.
  2. Take your BBT every morning as soon as you wake up. Taking your basal body temperature at the same time, from the same place in your body, before you do anything else will give you the most accurate results. 
  3. Record your temperature readings every day. You can do this on paper or using fertility tracking apps.
  4. Establish a baseline over time and track patterns so that you can understand when in your cycle you’re most fertile. 

You first need to know what your body temperature usually is in order to recognize when it increases, and determining this baseline takes time. Generally, you will need to track your BBT over the course of multiple menstrual cycles to get a sense of your body’s patterns and find your fertile window.

The BBT tracking method requires vigilance and organization, and it’s easy to get some of the details wrong. If you’re tracking your basal body temperature to avoid pregnancy, it’s recommended that you talk with a fertility awareness specialist to make sure you fully understand how to use the method correctly. Fertility awareness-based methods of contraception, including basal body temperature tracking, have a typical failure rate of 24% overall.

Should you use basal body temperature tracking to find your fertile window?

So, can tracking your BBT truly help you understand when you’re most fertile? The answer isn’t that straightforward, and there are both upsides and downsides to using BBT tracking as a fertility tracking method.

The pros


There’s a lot to like about basal body temperature tracking. First off, it’s inexpensive. You don’t need special equipment other than your BBT thermometer, a relatively easy to find tool that generally costs under $20. And you don’t need to make or go to a doctor’s appointment: you can track your basal body temperature from the comfort of your own bed.


Additionally, it’s a non-invasive method of fertility tracking. There are no surgical procedures required, no medication, no blood tests—it’s as simple as sticking a thermometer in your mouth (or rectum, or vaginal canal) and recording your temperature.

>>MORE: Looking for an easy-peesy fertility kit? Oova’s test kit helps you find your fertile window by just peeing on a test strip — no blood work needed.


Low risk

If you’re using the basal body temperature method to achieve pregnancy, there are no physical or medical side effects and no risks. If you’re using BBT tracking as a form of contraception, there is a higher risk that you may become pregnant compared to other methods of birth control.

The cons

Basal body temperature tracking also has quite a few drawbacks as a method for understanding your fertility. 

Difficult to get consistent readings

For example, your BBT can be a bit finicky. For accurate BBT readings, you have to take your temperature first thing in the morning. Little things like getting out of bed, using the bathroom, eating, drinking, or even talking can affect your BBT. If you take your temperature at 8 a.m. one day and 10 a.m. the next, this difference in time can also alter your results. The way to get the most exact readings is to take your temperature right when you wake up, at the same time every day, and this is sometimes easier said than done.

Hard-to-read results

Even if you follow BBT measurement instructions exactly, the results may not tell you much. In some people, a rise in temperature may not occur until 3 days after ovulation. Other people may not experience a change in temperature at all. This makes it harder to determine your fertile window based on your basal body temperature.

Easily affected by outside factors

Factors other than ovulation can also cause your BBT to fluctuate, which can make the method unreliable. If you’re monitoring your fertility with BBT tracking alone, it can be difficult to know if the changes in temperature that you record are caused by ovulation, or by something else. 

Other factors than can affect your BBT include:

  • Health changes such as illness or fever
  • Gynecological disorders
  • Emotional or physical stress
  • Alcohol consumption
  • Sleeping too little or too much
  • Seasonal changes or changes in climate
  • Changes in room temperature
  • Shift work
  • Travel
  • Changes in time zones
  • Certain medications

>>RELATED: Learn how alcohol can affect your fertility.

Basal body temperature can also be tough to track for people with irregular menstrual cycles. It’s hard to find patterns in your body temperature when your month-to-month changes frequently, and this can make your BBT an inconsistent measurement.

It’s also important to note that measuring your basal body temperature is not actually a way to predict fertility—it just tells you that you could have gotten pregnant in the days prior. Because the rise in BBT occurs after ovulation, it’s likely that you’re no longer fertile by the time you note a change in your temperature. In fact, it’s more accurate to say that an increase in your BBT is the sign that your fertile window has ended.

Even under the most reliable circumstances, tracking your BBT to understand your fertility involves a bit of guesswork. In most cases, BBT tracking alone is an insufficient method for determining when you’re most likely to get pregnant.

Combining basal body temperature  tracking with fertility tracking methods

Many doctors still recommend using your basal body temperature to track your fertility, particularly for its low-cost and non-invasive nature. To truly understand when you’re most fertile, however, it may be useful to combine this method with other forms of fertility tracking.

At-home fertility testing kits are a great option for getting a more in-depth look at your fertility. Oova offers at-home urine test kits that analyze your body’s levels of luteinizing hormone (LH) and progesterone, two hormones that are essential to ovulation and pregnancy. With Oova test strips and the Oova app, you can get detailed information about your fertility window and whether or not you’ve ovulated.

Instead of thinking of basal body temperature tracking as the way to track your fertility, think of it as one tool in your toolbox. You’re most prepared when you use a combination of the tools available to you. Combining BBT tracking with other fertility tracking methods, like at-home fertility testing kits, can give you a fuller picture of your fertility and help set you up to get pregnant.


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