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Did you know that your temperature changes throughout your monthly menstrual cycle? Or how about that you can use this data to predict your fertility window and—more specifically—when you’re ovulating? The variation is slight (to the tenth degree), but with the right tools and a bit of learning, we can use this information to track our cycles, even if they’re irregular

But let’s back up. What even is a basal body temperature, and how does it differ from the regular ol’ temp we take when feeling a bit under the weather? 

Your basal body temperature (BBT) is your body’s temperature when it’s fully at rest—i.e., your temp first thing in the morning. For most ovulating people, it ranges between 96°F (35.5°C) and 98°F (36.6°C), and the tenth of a degree variation is dependent on where you’re at in your cycle. 

Here’s an example. The below chart, shared with permission from one of our editors, shows an average BBT of 97°F–97.4°F before ovulation (the follicular phase) and an average BBT of 97.5°F–97.9°F after ovulation has occurred (the luteal phase). 

Notice how, on day 13, her temperature dips slightly. This happens just before an egg is released from an ovary, meaning she’ll ovulate sometime in the next 12–48 hours. If she were trying to avoid pregnancy, she would want to refrain from unprotected vaginal intercourse in the five days leading up to this dip and in the 48-hour window after. Alternatively, if she were trying to get pregnant, this would be the optimal window for conception. Once her body temp rises above the coverline—the horizontal line that “separates average temperatures before ovulation from average temperatures after ovulation”—she can confirm ovulation has occurred.

Now, notice how her temperature remains elevated for the rest of her cycle, then begins to drop as she nears menstruation. This is thanks to progesterone, a hormone that prepares the body for a potential pregnancy. If a person is pregnant, progesterone levels (and daily temperature) remain above the coverline; if not, BBT falls as the uterus prepares to shed its lining, signaling the start of a period. In this way, monitoring your BBT can also be an early indicator of pregnancy.

All this to say, our bodies are pretty incredible! And if our cycles are regular, we can use a basal body thermometer (ideally alongside other tracking methods, like cervical mucus monitoring and ovulation strips) to help with fertility awareness, whether we’re trying to prevent pregnancy or hoping to conceive. Even with irregular cycles, BBT monitoring can be a valuable tool to help identify ovulation with your doctor. 

A quick note: It will take a couple of months of diligent tracking to begin noticing patterns in your temperature and cycle. If you are sexually active and trying to avoid pregnancy, we recommend talking with your doctor first and considering additional protection (like these vegan condom brands) while you collect data and become familiar with your BBT. As with anything related to our bodies, it’s important to remember that each individual is unique. What may work for one person is not necessarily a great option for another. Not everyone experiences a rise in temperature after ovulation, and hormone imbalances or lifestyle changes can alter your BBT.

That said, BBT tracking can be a great tool for many people, even just to become more in tune with your body. So, whether you’re looking for a natural birth control option, planning for a baby, or you just want to learn more about your cycle, here’s how to use a basal body thermometer—plus a few options to try!

(Psst! And if you are looking to get pregnant, start taking the prenatal vitamins now!)

1. Find A Thermometer That’s Right For You

In today’s tech-savvy world, there are numerous BBT thermometer options on the market. What’s most important is identifying the thermometer that will work best for you and your lifestyle. Here are six picks we love ranging in price and function: 

1. Ava Fertility Tracker Bracelet, $279+

The first and only FDA-cleared fertility bracelet with data security guarantee. Ava monitors additional physiological signals for more accurate readings and tracks sleep and stress. This BBT has payment plan options, international shipping available, and is female co-founder.

2. Natural Cycles, $15

This BBT thermometer offers an affordable, simple design with Celsius and Fahrenheit options. The Natural Cyles app is FDA-cleared (also certified in Europe and listed in Australia), and the thermometer comes with a two-year warranty. International shipping available and female co-founder.

3. Daysy 2.0, $319

This easy three-light thermometer shows you when you’re most fertile and comes with a free app (no subscription required). Daysy is FSA eligible, compatible with irregular cycles, and the brand offers climate-neutral international shipping. The company is family-founded.

4. OvuSense, starting at $35/mo

This skin-worn and vaginal sensor option works for people with PCOS and/or irregular cycles. It comes with a free app (no subscription required) and has class II regulatory approval in USA, Europe, Canada, and Australia. OvuSense is backed by clinical studies and offers international shipping.

5. Oura Ring Gen 3, $299+

Oura is a titanium ring that comes in five finishes, is water resistant, and has a seven-day battery life. It pairs with the Natural Cycles App for BBT monitoring and has its own app for one-stop monitoring (temperature, sleep, activity, recovery, heart rate, blood oxygen levels, and more). Verified by multiple independent studies and The Good Trade editor tested and approved.

6. Tempdrop Monitor 2.0, $199

This wearable skin sensor is an adjustable armband that continuously monitors your temp while you sleep (no need to wake up at the same time each day!). Tempdrop comes with a free syncing app with charting features, suits irregular cycles, is FDA-registered, and is HSA and FSA eligible.

2. Read The User Manual & Pick Your Charting App

First things first: Wash your thermometer according to the manufacturer’s instructions, then give the manual a read (or two) to familiarize yourself with all its functions and features. These days, most BBT thermometers come with a recommended app for easily recording your data. Many period tracking apps also have BBT charting options, and these fan favorites are even more specific to fertility and ovulation monitoring. Manual tracking in a notebook is also a great option if you prefer a paper record.

3. Take Your Temperature At The Same Time Each Morning 

Here’s where basal body thermometers get a bit trickier and where you have to practice discipline. To get the most accurate reading, you want to track your temp at the same time each morning—before even rolling over or sitting up from bed (yes, seriously!).

You need to take your temperature first thing after waking up while you are still lying down. Pop it in the back of your mouth under one side of your tongue, wait for the beep, then go back to sleep (if you want!).

Since most have a memory-saving device (some even pair with Bluetooth), you don’t even need to be fully awake to use it. You can then review and record your temperature once you’ve had your morning coffee. 

A few tips for more accurate readings:  

  • Don’t drink any beverages before testing.

  • Try to keep the thermometer still and at the same spot in your mouth.

  • For an even more accurate reading, pop it in your mouth for a few minutes before turning it on. This will be especially helpful with seasonal changes or if you’re running a heater/AC.

  • Record notes about your diet and sleep quality if relevant; for example, if you had wine the night before or got up in the middle of the night to use the bathroom, this will likely affect your temperature. 
  • If you have an inconsistent sleep schedule, a wearable tracking device may be best for you.

4. Analyze The Data & Avoid Sexual Intercourse (Or Don’t! 😉) 

After you’ve been tracking for a couple of months, you can start comparing data and watching for trends. Keep an eye out for dips and peaks and bring the data with you to your next OBGYN appointment—especially if you have questions about possible hormone imbalances, intense PMS symptoms, or spotting between cycles.

If you’re using BBT tracking specifically to avoid or try for pregnancy, you now have lots of insight about when (and when not) to have vaginal intercourse with your partner. Plan your rendezvous accordingly! 

Featured image is from Tempdrop