Basal Body Temperature (BBT): Tracking, Charting & More

Medically Reviewed By
Dr. Prerna More Patel (Gynecologist/Obstetrician)
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Tracking and interpreting basal body temperature is one of the methods employed by women who want to use natural contraception methods. It is also an indicator of the most fertile period for women who are aiming to conceive. This article helps you understand the ‘why’ and ‘how’ of the process, and guide you in creating a basal body temperature chart for yourself.

What Is Basal Body Temperature (BBT)?

Basal body temperature (BBT) is the lowest body temperature that is attained in a 24-hour period. This would obviously be when you are at rest. A thorough pattern obtained by a few months reading of your BBT will give you a better picture of your ovulation period and timings.

You should measure your BBT before you do any physical activity that might alleviate your body temperature. Ovulation may slightly raise your BBT levels,so noting down your BBT over time may reveal the corresponding variations. That is what makes the BBT a natural method to keep track of your menstrual cycle, especially if you are trying to get pregnant. If you measure your temperature after performing some physical activity, the false and somewhat higher value of BBT can result in wrongly identifying the phase of the menstrual cycle.

BBT levels are known to hike slightly during ovulation. Therefore, recording your temperature over a period of time will show you a pattern and variations whenever they occur. This way, you will be able to keep track of your menstruation cycle which is very helpful if you are trying to get pregnant.

How to Track BBT?

So, how do you measure basal body temperature? Let’s start with the basics first, by learning about the device used to measure it, which is a BBT thermometer.

Basal thermometers or BBT thermometers are recommended over digital thermometers to measure BBT as they are sensitive enough to record the most minute changes that occur in your body as compared to a regular thermometer. Use it to take your temperature the moment you wake up, even before placing your foot on the floor. Since BBT is usually recorded for a 24 hour period, try to wake up at approximately the same time every day for an accurate recording. This could also help regularise your sleep as an added advantage!

The usual value of BBT ranges from 97.2 to 97.7 degrees Fahrenheit,and ovulation could cause an increment in your normal recording by 0.5 to 1 degree. This would last until your period starts and is what will really help you confirm your ovulation. Your BBT could show some spiking on other days apart from your days of ovulation. However, this would only be for a day or two. Once you ovulate, your BBT tends to be at a higher observed value for all readings from that day until you menstruate.

In case you get pregnant after ovulation, BBT would remain high throughout your pregnancy, thus satisfying the condition that it would remain high until your uterus sheds again.

How Does a BBT Chart Help?

Maintaining a chart can make an otherwise seemingly tedious task interesting. It gives you a graph on joining the dots to see the spikes clearly. This kind of a chart can even help your obstetrician diagnose any fertility or other issues related to your menstrual cycle. Moreover, you can boost your chances of conceiving if you keep a track of certain factors related to your cycle on a daily basis.

What Is Cervical Mucus (CM)?

Cervical mucus is the vaginal discharge which is secreted by the cervix and its production is stimulated by the hormone oestrogen. The appearance and quantity of cervical mucus keeps changing depending on your menstrual cycle and on your moods or sexual activity. Most importantly, it protects against infection and irritation.

The consistency, colour and odour of vaginal discharge vary from person to person. However, generally, the colour varies from clear to white to slightly off-white, and the odour from mild to non-existent. There are also patterns observed based on the stage of the menstrual cycle:

  • Soon after your period, there is very little to no vaginal discharge (known as the ‘dry days) because of severely reduced oestrogen activity
  • After this, you may have a thick discharge (also described as cloudy)
  • As you progress towards ovulation, the discharge becomes softer and more liquid in form, allowing for optimum sperm travel (also called the ‘egg white’ stage)
  • After ovulation, the discharge becomes thicker but lesser under the influence of progesterone
  • This will be followed by your period, and the cycle continues

Predicting Ovulation Using BBT and CM

BBT combined with CM can be an effective and natural way for you to track ovulation and plan sexual activity accordingly. It could help know the right time to try insemination or avoid it if you are looking at natural methods to prevent pregnancy.

The signal for knowing when you are at your peak (fertility wise) is a soft, liquid egg-white discharge suggesting optimum conditions for sperm travel right before your ovulation, followed by an increase in your BBT, indicating ovulation.

Noting your CM with your BBT would be a good idea to take charge of things. Note that it will take time for you to develop the habit and notice the patterns.

How to Chart BBT and Cervical Mucus?

If you have a relatively regular cycle, you should be able to plan sexual activity from when you notice the CM becoming egg white and stretchy. You must start trying before the increase in BBT if you want to conceive.

It is better to note the quality of your discharge in the morning. Sometimes you might have to insert a finger up your vagina to clearly examine the nature of your discharge.

Chart your CM and BBT recordings from the first day of your period as soon as you wake up.

Recording Your BBT Chart

There are several templates available on the internet to chart your BBT and CM. We have included a few towards the end of this article. Use the following steps to record your BBT and CM:

  • Begin recording from the first day of your period
  • Plan to wake up at the same time every day
  • As soon as you wake up, even before sitting up, take your BBT reading and mark a point against the day’s temperature reading. (Place your thermometer at an arm’s distance.)
  • Make a note of the date and time
  • Move to the washroom to examine your mucus quality. You could do this before you use the washroom in the morning. If you are checking after, be sure not to wash it all off. You could even observe the CM on the toilet paper after you wipe
  • Make a note of the CM based on the key provided in your chart. For example, the chart from White Lotus Clinic (see below) has CM types as P= period; D= dry; S= sticky rice; E= egg whites
  • As you make recordings, notice that the rise in BBT is usually preceded by the CM turning egg white. The CM turning egg white is when you are most fertile, and a higher BBT will help confirm ovulation.

Phases in BBT Chart

In case you were wondering how to measure basal body temperature, the whole process is explained in a clear manner below. Read through the different phases and know how to mark the chart accordingly.

Women with fairly regular menstrual cycles have two distinct phases in their BBT charts:

  • Follicular Phase – You are in this phase from the first day of your period until ovulation. Higher oestrogen activity leads to low temperatures in the range of 97.2 to 97.7 degrees Fahrenheit. As you approach mid-cycle, there might be a sudden noticeable drop which signifies ovulation.
  • Luteal Phase – After the sudden drop in temperature, BBT shows a sudden spike and remains high for the rest of the cycle due to progesterone activity. This is why the spike in BBT confirms ovulation. BBT ranges from 97.7 to 98.3 degrees Fahrenheit during the luteal phase.

For a lot of women, on impregnation, the graph would show a third phase, a second rise in body temperature of about 0.7 degrees Fahrenheit more than in the luteal phase; 7-10 days after ovulation. Check this completed BBT pregnancy chart to see the third phase.

Sample BBT Chart for Reference

Here are a few ovulation chart examples of completed BBT-CM, so you get an idea of what they look like after filling:

Source: White Lotus Clinic


How to Read a Basal Body Temperature (BBT) Chart

The answer to the question of how to read a BBT chart is fairly simple and can be explained in a few simple steps. This chart is also called BMT chart (This is for a regular 28 days menstrual cycle).

  • The temperature remains at low values from day 1 to day 13
  • On day 14, when ovulation occurs for most women there is a sudden dip (marking the end of the follicular phase)
  • There is a marked spike on day 15 (beginning of luteal phase)
  • The days from 16 to the next day 1 show fairly higher temperatures than usual. So, you get a BBT graph at the end of each cycle.

The sample BBT chart showing pregnancy shows a second rise in temperature from Day 25:


Blank BBT Chart for Printing

Here is a sample template that you can take print out of to make your own BBT-CM chart:

Source: Freeprintablemedicalforms

There are fixed spaces to note every little detail, from the dates covered to the cycle number and specifics for each day of the period. You can note the date, day of the week and the time at which you note the BBT. Mark a dot against the temperature observed. Examine CM type according to the key provided and enter the corresponding letter. Tick or cross the days that you had sex on.

Women tend to lose track of their period and often fumble even when asked about the typical lengths of their periods by the gynaecologist.

A lot of symptoms including susceptibility to cold and digestive sensitivities can often be explained based on your menstrual cycle. Also, natural methods are better than any external intervention to plan your pregnancy.

Understanding your BBT chart will help you take things into your own hands and understand the signals your reproductive system gives you. Tracking your BBT and CM helps you plan better at your own end. Whether or not you are planning to start a family, these indicators will surely be of huge importance to make that call.

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