How to Take and Record your Basal Body Temperature - BBT

Lesson 8

Lesson Objectives:

  • Learn how to accurately take and record your BBT

  • Learn how to identify factors that may affect your BBT curve

Major Points in this Lesson:

The following guidelines should be followed when charting BBT:

  • Take your temperature at as close to the same time every morning as possible.

  • Take your temperature as soon as you wake up, after a solid block of sleep, before moving around.

  • Use an accurate thermometer (fertility/basal thermometer available at your drugstore/pharmacy).

  • Record your temperature as soon as possible after taking it.

  • You can take your temperature orally or vaginally, but you must be consistent throughout the cycle.



It is important to use an accurate thermometer. We recommend using a digital BBT thermometer. A digital BBT thermometer gives a quick reading, beeps when it is finished recording the temperature, and is easy to read. This can make a difference when you are bleary-eyed first thing in the morning. Your thermometer will likely store your reading for you, though we recommend to record it right away, either using a bedside notepad or using your Fertility Friend Mobile App on your smartphone.

Digital BBT thermometer are inexpensive and available at most drugstores and online retailers. The brand does not matter much but you may want to look at the features provided (such as memory or backlighting).

If you are using a wearable/connected temperature sensor, make sure that the temperature it provides is a true basal body temperature. Some sensors are unable to provide this or provide you with some calculated/simulated temperatures which may skew the interpretation of your data. Please contact the device manufacturer to know if the temperature it displays can really be used as BBT. If in doubt we recommend to use a regular BBT thermometer as well if only to calibrate your sensor. You can use Fertility Friend custom data and chart duo capabilities to record and display two temperature graphs on your chart if needed. See the Wearable Technology For Fertility article on the web site for details. If you are using a wearable make sure to update your temperature method in your Charting Settings.

Routine and Habit

It is best if you can establish a routine where you enter your data at the same time every day just to form the habit so you will not forget. Missing data, especially temperature data can skew the interpretation of your chart. Once a routine is established, taking and recording your temperature will probably start to feel as natural as brushing your teeth.

Important Guidelines

Your temperature data will be most reliable if you follow these guidelines. Not following these guidelines may make your chart difficult to read and may make detecting ovulation more difficult as well.

Please note that these are ideal guidelines. The realities of your life may make meeting these ideals difficult or impossible at times. Ovulation can usually be detected even under less than ideal condition. The closer you can get to the ideal, however, the more accurate and reliable your ovulation detection, analysis and interpretation will be.

  • Take your temperature before rising in the morning as any activity can affect your BBT.

  • Take your temperature at the same time every morning. We recommend using an alarm clock if possible.

  • Take your temperature after at least three consecutive hours of sleep whenever possible. No need to worry about the occasional bathroom trip though as long as you go back to bed.

  • Keep your thermometer accessible from your bed so you do not have to get up to get it.

  • If you are taking your temperature orally make sure to place the thermometer towards the back of your mouth and under the tongue for better accuracy.

  • Use the same thermometer throughout your cycle if possible. If it breaks or the battery dies and you use a new one, make a note of it on your chart.

  • Temperatures can be taken orally or vaginally but it is important to be consistent throughout the cycle since the temperature range may vary. Most women prefer to take their temperatures orally, however, when temperature patterns are unclear, switching to vaginal temperature-taking for the next cycle sometimes makes the pattern clearer.

  • Record your temperature soon after you take it (or ask your partner to) since most thermometers only store a reading until the next use. If you have to do something else or want to stay in bed, you can record it later, but we recommend recording it in your Fertility Friend App right away when possible to avoid forgetting. If you are charting on's desktop site, you can use a bedside notepad in case you are not able to enter your temperature on your chart right away.

  • If you must use a heating pad or electric blanket, keep it at the same setting throughout your cycle. Make a note of its use.

  • Always record the time you took it on your data entry page. The time you took your temperature is also important for the analysis. Fertility Friend App will do that for you if you record your temperature right after taking it.

If you have special circumstances on a temporary or an ongoing basis and you are unable to follow all of the above guidelines, keep taking your temperature anyway following the guidelines as closely as possible. Make a note of your special circumstances in the notes section of your chart. There is still a good chance that you will be able to chart and see your fertility pattern.

Data Entry

The BBT data entry form on your Fertility Friend App offers large numerical buttons to make it easy to enter first thing in the morning. You can also set an alarm within the app in the settings menu.

Temperature data entry

The data entry field for Basal Body Temperature on the web site is similar.

For more details about data entry using please [Click Here]. If you are using the mobile app, check the App Tutorial.

Once entered your temperature data will be displayed on your chart:

temperature chart

Influencing Factors

There are certain factors that can influence your basal body temperature. These should be noted on your chart. Fertility Friend's data entry page includes a series of checkboxes and a custom data from to make this easy. These factors, should they apply to you, will usually not make charting and chart analysis impossible, especially if they occur only rarely, though it may be more challenging. In most cases, even when these factors apply on an ongoing basis, they will not skew your data so much that reading the chart is impossible.

The following factors may influence your BBT and should be noted in your chart data:

  • fever

  • illness and infections (even those that do not produce a fever)

  • cold, sore throat

  • drugs and medications

  • alcohol (especially in large quantities, though all alcohol consumption should be recorded)

  • smoking (if you smoke, you should consider quitting before you are even pregnant)

  • emotional stress

  • physical stress

  • excitement

  • sleep disturbances (insomnia, night-waking, upsetting dreams, poor sleep)

  • change in waking time

  • jet lag

  • travel

  • change of climate

  • use of electric blanket

  • change of room temperature

  • breastfeeding

Further Reading:

Next Lesson: Cervix Position, Optional Fertility Sign.

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