How to Chart your BBT and Know When you’re Ovulating

This is a common question that comes up in clinic, so let’s talk BBT and how to know when you are ovulating. 

BBT Basics

BBT, basal body temperature, is a fertility awareness method that is most frequently used to predict ovulation in order to either achieve or prevent pregnancy. However, it can also be an adjunct tool for evaluating thyroid health in conjunction with lab tests. Our basal body temperature fluctuates at certain points in the menstrual cycle, signaling ovulation, the start of the menstrual cycle, or even a possible pregnancy.

First off, it’s important to know that basal body temperature is counted to the 1/100th degree, so you will need a thermometer that will give you two decimals- for example, 98.63. Taking your temperature with a regular thermometer only reads to the 1/10th degree (98.6) and usually won’t be specific enough to predict temperature rises and falls throughout your menstrual cycle. 

The thermometers that sync to your phone and are automatically charted for you are also great and super convenient. However, sometimes you will just need to download an app and chart your numbers every morning on your own. 

 How-To

Aside from having the right thermometer, and remembering to chart it every morning, it’s also important to remember to chart before getting out of bed and around the same time each morning upon waking. The consistency of taking your temperature every morning before you get out of bed at the same time will allow us to detect small changes in basal body temperature that signal your hormones are either rising or falling. Make sure you keep your thermometer within an arm’s reach from bed so you can easily chart it without getting up and moving around. Then, just place the thermometer under your tongue and wait until it has beeped for the results. Taking your BBT orally and placing the thermometer under the tongue is the standard. Start taking your BBT on the first day of your period and track it every day through your menstrual cycle. Then, once you start to find your pattern and notice which day you ovulate, you can skip day 1-4 while you’re menstruating and then start taking it on day 5 or 6. However, this only applies to people with regular menstrual cycles. 

Temperature Fluctuations during your menstrual cycle 

In general, your BBT is lower in your follicular phase, and higher in your luteal phase. In a healthy cycle, your temperature drops right before ovulation and then is the highest on the day of ovulation and continues to stay higher in the luteal phase. In order to count a temperature spike as your ovulation time, it needs to have risen at least .5 in temperature or stay higher than your average follicular phase temperatures for 3 days in a row. 

There are only about 5-7 fertile days in the menstrual cycle, and if you are looking to conceive, it is best to try 2-3 days before ovulation, or the day of ovulation. 

Your BBT then drops again when your hormones drop and you are about to get your period, (usually the day before or the morning of). And then the cycle starts all over again. If your temperature never drops when you should be getting your period, and your period never comes, this could potentially indicate an early pregnancy. Of course, this has to be verified by a pregnancy test!

Things that can skew BBT results

In cases of hypothyroidism, the basal body temperature is usually lower than normal (lower than 97.0) or perhaps show temperatures that are all over the place. The health of the thyroid is very important in pregnancy, so it’s a great idea to have this under control before trying to conceive. Taking temperatures at different times, after getting out of bed, lack of sleep or poor sleeping habits are known to skew temperatures as well. 

BBT and ovulation

One of the main advantages of taking your BBT is seeing when you ovulate, or if you are ovulating at all. If you have no sustained rise in temperature, it could be a sign that you aren’t currently ovulating. However, there are other ways to check for ovulation- like examining cervical mucous and using LH strips. We will talk further about this in another blog post. 

Some signs that you may not be ovulating might include: no sustained rise in BBT, irregular cycles, cycles that are abnormally short or long, very short luteal phase, no cervical mucous, very light menstrual bleeding.

If you aren’t ovulating, you cannot get pregnant. Therefore, this is one of the first things we like to check for any fertility challenges. 

Comment below if you have any questions! 

                      Follicular Phase                           Luteal Phase