BBT Charting for Beginners

If you’ve spent any time at all on any of the fertility forums and/or doing research into ways to help improve your chances of becoming pregnant, you will have inevitably heard the words:

Do you chart your BBT?”

If you are one of the ‘shy’ human types or like me, terrified to announce to the other women in the forum that I had NO idea what I was doing, you might not feel comfortable asking a stranger the ten million dollar question:

‘What the hell is a BBT, and why the hell should I chart it?”

The term ‘BBT’ is another one of the acronyms that us veteran TTC-ers throw around like candy, assuming that everyone else on the forum or reading the website already knows. If you’re not sure which acronyms I’m talking about, STOP and click here for a quick rundown of the most common acronyms you will undoubtedly encounter.

But I Digress

Your BBT is in fact your Basal Body Temperature, which is your body’s lowest temperature of the day. It is obtained immediately after waking first thing in the morning, before doing anything whatsoever. That means that to get an accurate BBT, you will need to take your temperature before even getting out of bed. Fun, right?

So how and why is this done, and what does it have to do with becoming pregnant? I’m glad you asked!!

The HOW portion to that question is the easiest part to explain, although it is also the hardest part to do. At least for me it was. Before you begin to chart your BBT (which is just another way to say that you are tracking your BBT), there are a few things you’ll need to obtain; luckily, none are very expensive unlike almost EVERYTHING else that’s related to TTC!!

The first thing you’ll need is a basal thermometer. And before you ask, yes there is a difference between a basal thermometer and a regular thermometer. The difference lies in how accurately your temp is measured. A normal, every day thermometer measures your body temperature to the tenth degree. (In case you slept through your junior high math class like I did – that means that there’s one number on the right side of the decimal point.) A basal thermometer however, measures your body temp to the hundredth degree. What’s the importance of the extra number behind the decimal point?

Sometimes your temperature can fluctuate just that small amount from one day to the next. And that’s important.

Here’s a good ol’ fashioned basal body thermometer that costs around $8 at Walmart.

Now if your pockets are deeper than mine (a lot deeper because I’m what you’d call a “cheap ass”) and you’re all about the convenience of technology, you can get a fancy pants thermometer that actually plugs right into your phone and automatically stores your temperature for you.

Exhibit A: The Kinsa Smart Thermometer which runs anywhere from $15-$20 online.

There are others out there that are considerably more expensive than even this Kinsa, but I’m not going to even mention them in any detail here. Why? Mainly because I personally believe that they are a complete and total waste of money, given that these two options are just as accurate and reliable. And well, see aforementioned comment about me being the world’s biggest “cheap ass.”

Unless specified otherwise, all basal thermometers can be used one of two ways; you can obtain your temp by inserting the thermometer under your tongue (by far the most popular method), or by inserting it vaginally and obtaining a reading that way. Believe it or not, vaginally is the most accurate way to measure your BBT, for one simple reason. Anyone ever been told that you sleep with your mouth open? When the mouth is open during sleep, the colder air around you can lower the temperature inside your mouth and cause you to receive an inaccurate temp. Inserting the thermometer vaginally will give you an accurate reading every time; I know plenty of people who sleep with their mouths open, but I’ve never met someone who sleeps with their “you know what” open!


The second thing you’ll need to get hold of is a BBT chart. Now, most of the TTC-ers that I know (lumping myself into this category), prefer to use one of the MANY apps on their smart phone that will chart your temps for you. My personal favorite was always the Fertility Friend app, which (in my humble opinion) is the easiest and most user friendly fertility app on the planet. Another good one out there is the Kindara app, although it is available (at least for now) only in the iTunes store for Apple users. And then of course there are also a number of actual websites where you can enter your daily temps in and have them charted for you, my favorite of that variety being Countdown To Pregnancy.

For those who prefer the good ol’ fashioned, no reliance on modern technology methods, there’s still a way you can chart your BBT without needing to input the information into your computer, tablet, or smartphone.

Here is a blank chart in Celsius.
And here’s one in Fahrenheit.

If you’ve decided to go it “old school style” and chart your temps by hand, you would simply find your EXACT temperature on the chart and make a dot (these particular examples only use one decimal point) every morning after you get your temperature taken. Then as you might suspect, you would simply draw a line between each day’s dot, creating a ‘chart’ of your temperatures.

Now onto the WHY question.

Charting your BBT daily (at the same time every day mind you, or it won’t be accurate), will give you a good indication as to what your hormones are doing, which in turn gives you a very good idea of what your girlie organs inside are doing. I used to set an alarm for 4:00 am to make sure I took my temp at the same time every day.

I won’t go into an overly long, in depth version of which hormones control what function in your nether regions, but I will say that the predominant hormone in the first half of your cycle (or follicular phase) is estrogen, which causes your temperature to be relatively low. There may be a slight dip in your temperature on ovulation day (not every woman will experience this, and each cycle may vary even with the same woman). The reigning hormone in the second half of your cycle (or luteal phase) is progesterone, which is necessary to sustain any pregnancy that may be achieved. Progesterone causes your BBT to rise and to stay elevated throughout the remainder of your cycle. This rise is called a thermal shift.

Here you can clearly see the thermal shift taking place after ovulation.

The two red lines intersecting at a perpendicular angle are commonly referred to as “cross hairs” or CH. The vertical line is centered over the day identified to be your ovulation day, or O day. The horizontal line is called the “cover line” or CL (in this example it is centered over 36.4° C. This is generally considered to be the temperature to which your post O temps should stay above.

Now if you were charting your temps by hand, you would most likely never even bother with the CL, because (in my experience) it doesn’t really matter. So long as you can see a clear thermal shift, you “should” be able to identify your O day.

*Note: Not all thermal shifts will be this drastic in nature. It’s not uncommon to have what’s called a slow rise after ovulation. It is generally safe to assume that once your temp has risen for three days in a row (regardless of how far they climb each day) and remain high, you can identify your O day.*

Here is an example without the CH and you can see that O occurred on cycle day (CD) 14.
This one has a CL but no vertical line on O day.


If you’ll notice, each of these four charts depicts ovulation taking place on “cycle day” or CD 14. According to most websites, books, and forums associated with TTC, the “average” woman will ovulate on CD 14, based off a 28 day cycle.

Now how many women do you know of that actually HAVE a 28 day cycle every single month?

The sentence directly above this one is the entire reason why charting your BBT is a good idea. In my almost 35 years of life, I have known less than a handful of women who actually have a 28 day cycle every month. And on top of that – not every women who has a 28 day cycle will O on day 14 of her cycle. Many women (again lumping myself into this category) have had enormous troubles getting pregnant simply because they’ve been timing their efforts around the wrong day!!

And as we all know, where TTC is concerned — timing is EVERYTHING!!

Charting your BBT every cycle will help you to nail down just when you actually O every month. It can’t “predict” ovulation since the thermal shift only happens after you have O’d, but charting for a few cycles can give you an pretty good idea of when during each cycle you can expect to ovulate.

EXAMPLE: If after charting for 3-4 cycles you notice that you usually O on the 16th day of your cycle, it’s reasonable to expect to O around this time most cycles.

Identifying your body’s usual O day, you will be able to better time your efforts of conception (AKA “Baby Dancing”, BD, or sex) around the release of the egg, thus increasing your chances of conception every month.

“What if I never see a thermal shift during my cycles?”

Occasionally, even if your reproductive health is perfect, you may experience what is called an “anovulatory cycle” meaning that ovulation did in fact NOT happen that cycle. Normally this will be evident in your BBT charts as there will be a lack of a thermal shift.

This is a real chart from an anovulatory cycle. Note the lack of a clear thermal shift and no CH.

If your charts are looking similar to this one and aren’t showing O at all, don’t immediately freak out and demand to see a fertility specialist, assuming that your girlie parts are broken! The first thing you should do is stop and analyze your charting methods to ensure that you have been charting correctly. Ask yourself a few questions first.

“Have I been temping at the same exact time every day? Have I been using the same method, either orally or vaginally? Have I skipped any days? Have I been sick?”

Often times there have been simple errors made in the process of charting that can easily account for the lack of thermal shift. When charting your BBT, absolute consistency is key! Temping at different times is the biggest mistake I see made by women attempting to chart their BBT; you will undoubtedly get widely varying temps if you take your temperature at 9:00 am one day and 4:00 the next morning. (Those ladies with rotating shifts at their jobs tend to have difficulty charting due to this reason.)

You will also need to stay consistent in your methodology as well. If you decide at the beginning of the cycle to temp vaginally, try hard to continue doing so throughout the rest of the cycle. Switching back and forth throughout the cycle could also throw off your temps enough to make identifying O day difficult. Try to avoid skipping any days as well, especially around the middle of your cycle. The last thing you want to do is forget to temp on what could end up being your O day!

Many apps (Fertility Friend included) also have a box to check that indicates if you were sick or ill on any given day. Many times it will take this into consideration when identifying your O day. So don’t be afraid to temp if you aren’t feeling well. If anything, it will keep you in the habit of doing it, so that you don’t get out of the swing of things!

If you’ve mentally gone over your charting methods and have found nothing amiss, yet have not seen a thermal shift to indicate ovulation in a cycle, you may very well have had an anovulatory cycle. As I mentioned above, anovulatory cycles can happen to the best of us, and are usually not a cause for concern. Continue through your next cycle and see if your body gets back on track. If you have a glorious ovulatory cycle next time, then roll with the punches and BD like crazy! If you have yet another anovulatory cycle, it may be time to give your GYN a call just to speak to him/her and see what their recommendations are. And YES, you can have a period without having ovulated; I used to do it every cycle.

“So will charting my BBT tell me if I get pregnant?”

The simple answer is NO. Nothing but a positive pregnancy test can confirm a pregnancy, but there are a few things that charting CAN do for you that may help in other ways.

Once you’ve correctly identified your ovulation day, you will have a much better idea of when you can take a home pregnancy test and get a reliable answer. Nothing is more frustrating for a woman who’s been TTC for a long time than to pee on a stick or POAS, and get a big fat negative or BFN result. Often times when the exact day of ovulation isn’t accurately determined, ladies begin testing too soon and receive an inaccurate result. While some lucky few will receive a super faint positive result on a pregnancy test at 7-8 days past ovulation or DPO; the vast majority of women won’t receive their first positive until 11-12 DPO. Refer back to my previous “timing is EVERYTHING” remark.

“What will my temps do AFTER I become pregnant?”

During the luteal phase of your cycle after ovulation, your temps rise due to the progesterone pumping through your system. If a pregnancy was not achieved, the level of progesterone will begin to drop until it reaches a level low enough to trigger your body to start your period. Since progesterone is essential to the sustainment of all pregnancies, if a pregnancy WAS achieved, the levels of progesterone will not begin dropping, and instead will slowly rise. So in theory, your temps should stay elevated after receiving a positive pregnancy test result.

Here’s a real chart from a cycle where a pregnancy was achieved.

I love this chart for a couple reasons. 1) It shows O taking place on CD 17 (instead of the “normal” CD 14), and it also beautifully illustrates the elevated temperatures you can expect to see after becoming pregnant; Fertility Friend changes the color of your line from blue to green once you have tested positive.

It’s important to remember that, while charting your BBT can give you some great information about how your own body works, charting may not be a great fit for everyone. Correct charting of your BBT takes work, and a great deal of diligence! Many ladies have found that it only adds another layer of stress to their TTC journey, which as most of us who’ve been at it a while know, TTC can be stressful enough!! The first cycle has always been the hardest in my own journey, as it’s during that cycle where you have to get into the habit of it all. Temping may or not work with your schedule or daily activities.

Whether or not charting your BBT will work as a part of your TTC routine, or whether or not you decide to even try – remember that you have to make the best decision you can about YOUR fertility journey. If there’s one thing that a decade and a half of TTC has taught me, it’s that each woman’s TTC journey is different, and no one can decide for her what is best. Hell, I’ve had two pregnancies and TTC for each one was a different journey. Do your research. If you’re unsure of something – ask. Don’t be shy; we all started out from exactly the same place.

Baby Dust
Wishing all my TTC ladies lots of luck Baby Dust!