How and Why to Track Your Basal Body Temperature

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Hey Lady,

A few weeks ago, I shared our 5-Step Pre-Pregnancy Checklist, with guidance about how to get started making your body a welcoming home for new life.

Second on that list is tracking your fertility signs, often called the Fertility Awareness Method. Megan shared all about Getting Comfy with Cervical Fluid, so now its time to dive into the hows and whys of temperature charting. (The Fertility Awareness Method also includes tracking cervical position, but honestly and personally, I never got the hang of it. If you’re ready to go deep, Taking Charge of Your Fertility is a must read).

What is Basal Body Temperature charting?

Your basal body temp (BBT) is taken very first thing in the a.m., before your feet hit the floor. Its a measure of your metabolic function at rest. What’s really cool is that immediately after you ovulate, your BBT spikes, and stays high until the onset of your next cycle (i.e. the first day of your period).

By charting your BBT every day, for a few months, you begin to identify patterns in the length of your follicular phase (pre-ovulatory; ranging from 7 to 21 days) and luteal phase (post-ovulatory; ranging from 10-16 days), and what day in your cycle you typically ovulate.

If coming off of hormonal birth control, it can take several months for your body to get into the swing of things and for patterns to emerge.

Why Should I Track my Basal Body Temperature?

First and foremost, this about taking charge of your health.

For so many of us, we were put on hormonal birth control at the first sign of acne, cramps or flirting with boys. While effective for staving off unwanted pregnancies, hormonal birth control masks natural cycles. BBT charting is a tool to learn about your body’s rhythms, when you’re fertile, when you’re not, and if all processes are in working order.

It’s all too common that women don’t discover conditions like PCOS or endometriosis until they stop taking birth control and realize how irregular, heavy or painful their periods become. When trying to conceive, it’s beyond frustrating to discover a diagnosis that should have been identified (and managed!) in your teens, rather than shoved under the birth control rug.

It’s also about taking charge of your fertility.

How do you know when you’re fertile?

One trap we see many women fall into is following the guidance of an app to determine their fertile window.

Most of these apps must have been created by men, because they assume we all have a 28 day cycle and ovulate on day 14. This is pretty far from reality.

If you look back at the ranges given above for the follicular and luteal phases, you’ll see that a normal cycle length is anywhere from 21-35 days. Ovulation can occur anywhere from day 7 to day 21. For a woman on either end of this range, an app predicting your ovulation at day 14 would miss your fertile window.

Back to temperature charting…

Because BBT tracking is how you figure out how long your follicular cycle lasts to accurately predict when you ovulate and when it’s time to get it on.

If you have trouble conceiving, your BBT chart can be extremely helpful to figure out why.

Here’s one example: Progesterone, among many other functions, is the hormone that promotes the growth of your endometrial lining. (Your endometrial lining is the tissue on the inside of the uterus that you shed each month with your period). It takes at least 10 days for the lining to grow thick enough for a fertilized egg to implant. If your BBT chart shows that you have a luteal phase shorter than 10 days, this is a clue that you might not be producing enough progesterone.

Here’s another example: If you find that your cycle is longer than 35 days, this likely indicates you’re not ovulating and should get screened for PCOS.

should I be tracking my basal body temp if trying to conceive?

How do I get started?

It’s super simple. Keep a digital thermometer next to your bed and the very first thing you do each morning (no, you cannot pee first) is take your temp.

Then, write it down.

You can return to grade school using a pencil and paper (here’s a blank chart you can print for tracking both your BBT and cervical fluid), or use an app (I use Ovia Fertility - if you know of a better one, please share in comments below).

Here is an example of what a BBT chart could look like, if you ovulate on day 14:

Example BBT chart for fertility

The spike in temperature on day 15 tells you that ovulation occurred on the previous day. You’ll see that slight variations from day to day is totally normal. The lower temp fluctuations mark the follicular phase; the higher temp fluctuations the luteal.

Here is a great resource, by the author of Taking Charge of Your Fertility for more charting options and examples.

note that bBT charting is not foolproof.

Your temperature can be thrown off by many things, such as stress, travel or illness. This is why we recommend stopping hormonal birth control and getting started with charting months in advance of trying to conceive, so you can start recognizing patterns, even if some months are a bit wonky.

Hopefully, you’re able to conceive easily by accurately predicting your fertile window. However, if things do not go so swimmingly, this chart cannot be used to diagnose anything, but it can provide extremely helpful clues to figure out what is going on as quickly as possible.

Finally, an (oversimplified) review of your cycle, because we could all use a refresher:

Female reproductive cycle

You were made for this!



PS Have questions about charting or tips that could help others? Please share in the comments box below or shoot as an email at