How To Use A Basal Body Temperature Chart To Detect Your Ovulation?

How To Use A Basal Body Temperature Chart To Detect Your Ovulation?

12 Sep 2022 | 8 min Read

Sudeshna Chakravarti

Author | 791 Articles

There are many tools that can help detect when you are ovulating to maximise your chances of pregnancy. One such option includes maintaining a basal body temperature (BBT) chart, to track your basal body temperature and pinpoint your ovulation.

This method is relatively easy and foolproof and recommended by many gyanecologists to help detect your ovulation period and better understand your menstrual cycle patterns. 

But how exactly does a BBT chart work, and is it 100% accurate? We discuss everything in this post and also give you a detailed guide on charting your BBT and identifying your ovulation cycle to boost the chances of a successful pregnancy. 

What Is BBT?

Basal body temperature chart
BBT is your baseline temperature that helps determine your ovulation cycle and most fertile days in the month / Image source: Shutterstock

To put it simply, BBT is your body temperature when you are at complete rest. However, the number can change depending on a couple of factors, including your hormones. The fluctuation in your BBT is what helps you mark your ovulation cycle. 

When you are ovulating, your body releases an excess of progesterone, which causes your temperature to rise. A rise in your BBT temperature indicates you are ovulating and you are at your most fertile days of the month.

You will also see a drop in your BBT just before your period, as progesterone production during this time drops (unless you are pregnant, in which case your BBT will remain high due to increased production of progesterone).

Also, there are some rules that you should follow while checking your BBT. Since BBT is the body’s baseline temperature when you are at complete rest, it’s best to determine the temperature first thing in the morning, before you get out of your bed or move around.

This is because moving around can raise your BBT and give you an inaccurate charting that might not help you determine your ovulation period.

Advantages of BBT Charting

There are several advantages of BBT charting. The most popular ones include:

  • It helps in tracking ovulation and determines if you have a consistent period cycle or not
  • It helps you plan when to have sex for conception
  • It helps detect possible fertility concerns, including abnormalities in your ovulation and luteal phase (time between ovulation and menstruation)
  • It helps your healthcare provider make an infertility diagnosis
  • A BBT chart can also help detect early signs of pregnancy

How to Choose a BBT Chart?

The first step to BBT tracking is getting a chart to record your temperature. You can use sample basal body temperature charts available in fertility books for guidance, or install fertility calendars on your phone to monitor your baseline temperature.

You can also make your own BBT graph at home. To make a graph, plot the temperature on the vertical axis, allowing one-tenth of a degree for each square. Next, plot the days of your cycle along the horizontal axis. As you continue to mark the graph each day, you will recognise a fluctuating pattern in your baseline temperature and detect your most fertile days easily.

In addition to using a BBT chart, you can also use an ovulation tracker to identify your most fertile days effectively and plan your pregnancy accordingly. 

How to Measure BBT?

Basal body temperature chart
It is advised to record your BBT right after you wake up in the morning

Measuring your baseline temperature is fairly easy. All you have to do is invest in a thermometer that is specially designed to track your basal body temperature. Ideally, all thermometers give you accurate results, but you should preferably opt for the ones that are accurate to 1/10th of a degree if you measure in Fahrenheit and 1/100th of a degree in Celcius.

Also, observe the following guidelines before measuring your BBT to get accurate results:

  • Maintain a fixed time: Make sure to record your temperature at the same time every morning. Yes, you can have a delay of about 30 minutes on a few days, but make sure it’s not more than that.
  • Restrict movement: Avoid sitting up, moving around, or going to the washroom before taking your temperature. For accuracy, make sure to record the temperature as soon as you wake up, and then move on to your day-to-day tasks.
  • Make sure you are well-rested: You should have slept for about 6-8 hours in the night to ensure accurate results in the morning. If you barely slept at night or stayed awake, then you may have major fluctuations in your temperature.

When to Start Charting?

You should start charting your basal body temperature on the first day of your period and continue tracking it every morning throughout your cycle. 

Once you are well-familiarised with your ovulation cycle, you can skip the first two days of your period, and start charting your BBT from the third day to the next cycle.

Identifying Your Ovulation Cycle

The major focus of your BBT chart should be to look for an overall pattern, rather than concentrating on temperature spikes here and there. Your temperature may rise and fall as your menstrual cycle progresses, but you should watch out for a biphasic pattern to detect your ovulation. This means that before your ovulation period, your temperature recorded will be lower, as compared to the ones recorded after.

For any set BBT chart, if you notice at least three higher-than-average temperatures in a row, then you have most likely started ovulating. Plus, if you track your cervical mucous, then you will be even more sure about when your ovulation began.

Getting Pregnant

You can use a BBT chart to plan a successful pregnancy by looking for patterns. Detect a consistent pattern in your ovulation cycle and use this information to plan intercourse for pregnancy.

For instance, if you have charted your BBT for three months and noted that you ovulate on the 11, 12, and 13th day of your next cycle, then you should probably plan to have intercourse between days 6 through 16, with a special focus on days 11-15. 

Other Data to Track

To make your BBT charting more effective, you should considering recording some other data too. 

  • Calculate the number of days you have sex
  • Keep track of your cervical mucous
  • Consider your lifestyle preferences and stick to a healthy diet and a regular exercise schedule

What if You Are Not Ovulating?

One of the advantages of charting your BBT is that it allows you to determine if you have a healthy ovulation cycle or not. In case you notice an irregularity in your ovulation cycle, you could have a possible infertility risk. 

The following signs can indicate that you are not ovulating:

  • Cycles that are abnormally short or long
  • An irregular cycle
  • No noticeable change in basal body temperature
  • An extremely short luteal phase (less than nine days)

Pregnancy and Your BBT Chart

Basal body temperature chart
Factors like an extended luteal phase and an implantation dip could indicate that you are pregnant

Can a BBT chart help determine your pregnancy? Yes or no! Here are four possible ways a BBT chart can indicate pregnancy or the possibility of pregnancy.

  • Implantation dip: This involves a one-day drop in your basal body temperature about a week after your ovulation. However, an implantation dip is nothing more than a mid-cycle dip in your temperature and is highly debatable if you consider this a sign of pregnancy. 
  • Triphasic patterns: This is a second temperature increase occurring about one week after ovulation. Noticing a triphasic pattern on the BBT chart is likely to indicate a potential pregnancy.
  • An extended luteal phase: If you’ve been having regular intercourse and don’t get your period even after the 18th day of your ovulation cycle, then chances are you are pregnant. A good way to confirm will be by taking an at-home pregnancy test and then visiting an ob-gyn for further guidance.


Maintaining a basal body temperature chart is a great way to track your period cycle and ovulation patterns. It also helps you identify a pattern and plan your pregnancy accordingly.

Having a BBT chart can also help your gynaecologist determine if you are having a regular ovulation cycle and if there are any abnormalities in your luteal phase. 


What should your BBT be for a positive pregnancy?

Your BBT should increase and range between 97.6°F and 98.6°F for a positive pregnancy. 

What should your BBT be when you are ovulating?

When you are ovulating, your BBT should range between 97°F to 97.5°F.

What is a BBT chart supposed to look like?

A normal BBT chart should have a biphasic pattern, resembling a bird flying upward.

When should BBT drop if you are not pregnant?

In the absence of pregnancy, your BBT will drop one to two days before menstruation.

Cab BBT confirm your pregnancy?

If you have had a high BBT for 18 days or more, and aren’t menstruating, then chances are you are pregnant. 

Also read:

Ovulation symptoms: Check out this post to understand the symptoms of ovulation and when to seek medical help.



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