Intro to Basal Body Temperature Charting

Women's hormones change so significantly during the course of their cycles that just by looking at graphs of daily temperatures you can see when ovulation occurs, if implantation has taken place, or when the period is about to start. It can even spot subtle signs of hormone imbalance, for example, if enough there's not enough progesterone being produced to sustain pregnancy.

Not just any temperature though, specifically our basal body temperature (BBT) is what must be measured to better understand what our hormones are doing. Basal refers to the bottom, in this case it's the lowest our temperature gets each day. For most people, that happens to be when you first wake up in the morning, after your body and metabolism have been resting several hours.

I wrote earlier about the Fertility Awareness Method (FAM,) which uses temperature charting as a major component of tracking the menstrual cycle and determining a woman's fertile window. Click the link above to learn more about FAM and if it's right for you.


How to start charting BBT

So, you've got to start taking your temperature every morning, but it's not quite as simple as that. There are some specific parameters to follow to make sure your BBT chart is as accurate as possible:

  • You need a thermometer that's specific for BBT charting. Most regular thermometers that are sold in the first aid section of the drug store only have 1 number after the decimal point. Since BBT charting involves such slight variations in temperature you need a thermometer that measures 2 numbers after the decimal point, these are usually found in the family planning/contraceptives section of the drug store.
  • Take your temperature within 15 minutes of the same time every day. If you don't get up at the same time every day then set an alarm to get up, then go back to bed. It's okay if you can't make that happen 1 or 2 days of the week, but more than that and you won't have enough information to tell you much about your cycle.
  • Ideally you should have been asleep for 4 hours before waking and taking your temperature. Again, if you can't always make that work, it's okay, just do your best.
  • Don't get out of bed or drink water before taking your temperature. Remember, this is the lowest your body temperature is all day, if you move or drink/eat anything you're going to change the temperature of your body.
  • You need a place to chart all these temps. Some women prefer old fashion pen and paper, I usually recommend downloading a BBT charting app such as Kindara or Fertility Friend to keep track of your temps and fertile symptoms.


Is BBT charting right for you?

BBT charting is super helpful for tons of women, especially women who are actively trying to conceive or those who want to better understand their cycles. It can be used to effectively time intercourse for natural conception, and it can also be used to understand when you're most fertile in order to avoid pregnancy. Charting can be used alone or incorporated with other Fertility Awareness Methods.

If you looked at the rules above and thought to yourself they are absolutely prohibitive and would never work for you, that's completely understandable! Some women who suffer from insomnia or who have a toddler in the house can't imagine being asleep for 4 hours before waking. Other women can't stand the idea of waking up at the same time every day or waking up early on mornings they'd rather sleep in.

Plain and simple, BBT charting works for some women and not for others. Sometimes it's helpful to do for a few cycles and if a woman finds she's ovulating on the same day every cycle, then she may just use her calendar to estimate ovulation and stop charting her BBT.

I've also found that BBT charting can spike anxiety in some women, especially women who are trying to conceive. If you find yourself obsessing or worrying about charting, I recommend you take a break or use other methods to track ovulation, such as hormonal tests.


Need help interpreting your chart?

That's a bit advanced for an intro course. I'll cover that in a future post about what your BBT chart is telling you.