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Written by
Paige Figueroa
Women’s Health Writer -
Verified by
Dr. Aditi Neelakantan
Medical Practitioner, MBBS
Dr. Aditi Neelakantan
Dr. Aditi Neelakantan, a medical practitioner with a strong inclination for compassion-driven research, believes that “knowledge is a commodity to be shared”. She dedicates her time to simplifying complex medical information so that people can better understand their health and make informed choices.
Published on 30 December 2024
- Published on 30 December 2024
-
Written by
Paige Figueroa
Women’s Health Writer -
Verified by
Dr. Aditi Neelakantan
Medical Practitioner, MBBS
Dr. Aditi Neelakantan
Dr. Aditi Neelakantan, a medical practitioner with a strong inclination for compassion-driven research, believes that “knowledge is a commodity to be shared”. She dedicates her time to simplifying complex medical information so that people can better understand their health and make informed choices.
Published on 30 December 2024
- Published on 30 December 2024
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For decades, women have used basal body temperature (BBT) as a method for tracking their fertile window. In fact, one study of over 5,000 women found that 21% of them tracked their BBT.
Here’s the idea behind this method.
Post-ovulation, your basal body temperature rises sharply by about 0.5 to 1 degree Fahrenheit. If you end up getting pregnant, your BBT stays high. And if you don’t get pregnant, it drops back down.
While basal body temperature tracking is popular, it’s actually not a very reliable method. This goes for tracking both ovulation and pregnancy.
So whether you’ve attempted BBT tracking or not, keep reading to learn all the ins and outs of using BBT for tracking your menstrual cycle and fertility.
Takeaways
- Basal body temperature (BBT) is the measure of your at-rest body temperature.
- You can measure your BBT using a basal thermometer (which you can easily buy in many stores in person or online).
- BBT should be measured the same way and at the same time (right when you wake up) each day to get the most accurate results.
- Many women track their BBT in order to help track ovulation. This is because after ovulation, there is usually a 0.5 to 1 degree Fahrenheit increase in BBT.
- On its own, the basal body temperature method is not the best ovulation tracker. This is because the rate of accuracy is pretty low (at only about 22%). There are also lots of factors besides fertility that affect your BBT. Some include stress levels, sleep habits, illnesses, and even room temperature.
- If you become pregnant, your BBT will typically stay high. And if you’re not pregnant, it will drop back down to its natural baseline. But it should not be used on its own as a reliable indicator of pregnancy.
- There are many other fertility awareness based methods to use in addition to or instead of the basal body temperature method. Some are OPKs, follicular scans, checking your CM, or a fertility monitor like Inito.
What is basal body temperature (BBT)?
See AlsoFertility Tests for WomenFemale Fertility Tests - How Do You Know if You Can't Get Pregnant?Fertility Tests: What They Are & How They WorkFertility Tests for Women: A Comprehensive OverviewIn the simplest terms possible, basal body temperature is your baseline temperature.
In other words: your body’s lowest natural temperature as measured after at least three hours of uninterrupted sleep. In the fertility world, it’s known for its use in confirming ovulation.
Still scratching your head a little? No worries, we’ll break it down even more in the next section.
What’s the difference between your regular body temperature and basal body temperature?
Your body temperature can be measured at any point in time during the day. And all you need to measure your body temperature is a regular digital thermometer.
Basal body temperature works slightly differently though. Remember, it’s your body’s natural temperature after a period of prolonged rest (at least three hours).
In order to measure your BBT, you’ll need to use a basal body temperature thermometer. A basal thermometer gives you a more accurate reading with two decimal places.
Now let’s get to the real question on your mind…
How does knowing your BBT serve you when it comes to tracking your menstrual cycles? In the next section, we’ll show you how your BBT can change in each cycle phase.
How does BBT vary throughout your cycle? Why is it important?
Your basal body temperature fluctuates over the course of your menstrual cycle.
Here’s a quick snapshot of how BBT generally syncs up with the four cycle phases:
Phase of menstrual cycle | How your BBT changes |
Follicular phase (first half of cycle) | BBT is at its baseline Around 97-98 degrees F (or 36.11 – 36.67 C) |
Start of fertile window (4 days before ovulation) | BBT begins rising by about 0.33 degrees F from your baseline |
LH surge (24 – 36 hours before ovulation) | BBT begins dropping |
Luteal phase (after ovulation) | BBT increases by about 0.5 – 1.0 degree F |
Menstruation (on your period) | BBT drops back down to baseline |
Please know that this BBT chart should only be used as a reference point. Each person has a unique baseline BBT, and there are many other factors that can affect your BBT besides your menstrual cycle.
As you can see in the chart though, after ovulation there’s a rise in BBT by about 0.5 to 1 degree Fahrenheit. This rise is caused by the ruptured ovarian follicle (the corpus luteum) releasing progesterone.
The hormone progesterone signals to your hypothalamus to achieve a higher BBT. Since your progesterone stays elevated until your menstrual period comes, your BBT stays higher too. This is the reason why so many women use BBT tracking for fertility. It can help with pinpointing when ovulation happens.
How to check basal body temperature?
As mentioned earlier, for BBT tracking you’ll want to use a special thermometer called a basal thermometer.
This type of thermometer gives you temperature readings up to two decimal places. This is important since BBT variations are less than 1 degree F.
Once you have the right thermometer, here’s how to track BBT:
- Right when you wake up each morning (before doing anything else), take your BBT.
- Keep track of your BBT reading somewhere. If you’re a pen and paper gal, use a notebook. If you’re tech-savvy, use your favorite ovulation-tracking app like Inito.
- Be on the lookout for seeing your BBT rise by about 0.5 – 1 degree F (this is the sign that ovulation likely happened)That’s really all there is to it.
But a few extra measures to make sure you adhere to –
- Be sure to take your daily temperature readings at the same time each day.
- Make sure you use the same temperature measuring method each time.
For example, always do an oral reading or always do a rectal reading. This will help keep your BBT readings consistent.
Hopefully, all of this has demystified the BBT tracking process for you! But let’s go over a few more important things to keep in mind with this cycle tracking method.
How is BBT used for tracking ovulation? Is it accurate?
The most important thing to realize about BBT is that it doesn’t help you predict ovulation. Instead, it is used to help determine if ovulation happened or not.
This is a huge distinction because BBT only tells you about ovulation after the fact. It doesn’t help you predict your fertile window when TTC.
But if you do decide to use this method, you’ll need to track your BBT consistently each day so that you can catch that 0.5 – 1 degree F rise. That’s the sign to look for that tells you ovulation likely happened.
We say “likely” because BBT tracking isn’t an exact science for confirming ovulation. In fact, one study found that BBT readings only coincided with ovulation day in 22.1% of cycles.
This low accuracy could have to do with unique patterns of basal body temperature fluctuations. It could also be because other factors—like stress, room temperature, illness, or exercise—all affect your BBT.
Now that you have the key basal body temperature facts, let’s see an overall look at the benefits and drawbacks.
What are the pros and cons of tracking BBT?
Take a look at the upsides and downsides of tracking your basal body temperature in the table below
As you can see, there’s no harm in tracking your BBT. But at the same time, it’s not the most useful data point (on its own) for ovulation confirmation and fertility tracking.
Curious about how other ovulation tracking methods compare? Let’s go over your other cycle tracking options next.
Other methods of tracking ovulation besides BBT
1. Keeping tabs on your cervical mucus (CM)
Keeping a close eye on your cervical mucus throughout your cycle may cue you into when to expect ovulation in natural cycles.
A few days before you ovulate, you may notice increased amounts of CM. It’s likely to look either watery or like an egg-white texture (egg-white cervical mucus (EWCM)), and it can indicate high fertility. Think of it as your body’s way of telling you that it’s ready for intimacy so you can get pregnant
Know more: What Does Your Cervical Mucus Tell You About Your Body?
2. Going for a follicular scan:
Follicular scans are a great method because they are incredibly reliable. During a follicular scan (which happens via a transvaginal ultrasound), a fertility specialist is able to track your follicular growth. By tracking this growth, the doctor is able to accurately predict when the ovary is about to release a mature egg.
You’ll have a series of scans starting early on in your cycle, but the exact number of scans needed can vary based on how your cycle progresses.
The main drawbacks to this method are that it can be more expensive and may require some extra coordination.
So here are some helpful pieces of advice if you’re considering this route:
- If you have insurance, be sure to check with your provider to see if follicular scans are covered.
- Consider how far away the fertility clinic is so you can plan your schedule to accommodate each scan.
Know more: A Closer Look At Follicular Scanning For Ovulation Tracking: Is It Worth All The Inconvenience?
3. Using ovulation predictor kits (OPKs)
Ovulation predictor kits are urine tests you can take at home to predict ovulation. An OPK works by detecting the amount of LH present in your urine.
OPKs are less costly than follicular scans and can be done in the comfort of your own home.
But ovulation predictor kits also have drawbacks you should be aware of:
- Some brands of LH strips can give inaccurate results. This is because the test strips measure only alpha LH which may cross-react with other hormones or they may have low LH sensitivity.
- The majority of OPKs only give you LH results based on threshold values (usually around 20 – 25 mIU/mL). This means if your LH surpasses that threshold, you’ll get a positive result, even if you’re not about to ovulate. On the flip side, you could have an LH surge that doesn’t reach 25 mIU/mL and still ovulate, but your OPK would show a negative result.
- OPKs aren’t able to confirm ovulation. This is because LH is useful in predicting your fertile window, but progesterone is the hormone that rises and confirms ovulation.
4. An advanced fertility monitor like Inito
The Inito fertility monitor is a great tool for both predicting your fertile window and confirming ovulation.
Here’s how Inito overcomes some of the challenges of other tracking methods:
- It measures beta LH (OPKs can give inaccurate results because they only measure alpha LH)
- You get personalized, numerical values of your hormones. The results are not based on thresholds, and you can see the actual fluctuation patterns.
- It provides a complete picture of your cycle. Inito measures your LH, estrogen, and FSH to tell you your most fertile days. And it also tracks your PdG (urine metabolite of progesterone) which confirms when ovulation occurs. (Best of all, it does this all on one test strip!)
Let’s say you have been tracking your cycle and you end up conceiving. How does your BBT factor into signaling that you’re pregnant? We’ll cover this next.
Basal body temperature chart: pregnant vs. not pregnant
Pregnancy does affect your basal body temperature.
If you become pregnant, your progesterone will stay high which causes your BBT to also stay high. On the flip side, if you don’t conceive, your progesterone levels decrease. And this causes your basal body temperature to decrease before your period comes.
There are many factors that can affect your baseline body temperature. So you shouldn’t use this tracking method on its own to detect pregnancy. Only a pregnancy test can tell you for certain if you’re pregnant or not.
Another BBT trend to be aware of is the “implantation dip”. If you conceive, on the day that the embryo implants (usually between 8 – 10 DPO), there may be a temporary dip in your BBT. This dip doesn’t last long though and usually bounces right back up the following day.
As of now, this is only anecdotal evidence based on women reporting their BBT trends. There haven’t been any official studies that have examined the true nature of this dip around implantation.
FAQs
What can affect basal body temperature?
Your hormones (especially progesterone) greatly influence your basal temperature. But there are many other factors too such as your exercise and sleep cycles, the temperature of the room you’re in, and even your stress levels. That’s why the basal body temperature method shouldn’t be used as your sole method of fertility tracking or natural family planning.
How long after ovulation does BBT rise?
BBT usually rises right after ovulation and then stays high throughout your luteal phase.See AlsoThe Complete Guide to Fertility Tests - Fertility Cloud
How to measure basal body temperature?
Your basal temperature should be measured using a basal thermometer. This special thermometer gives you body temperature readings up to two decimal places. Most digital thermometers only give you one decimal place.
When does BBT drop if not pregnant?
After you ovulate, your BBT stays relatively higher in your luteal phase. If you’re not pregnant though, it will drop back down a few days before your period comes.
What’s your basal body temperature if pregnant?
The exact basal body temperature varies slightly from woman to woman. What’s more important is how your BBT changes after you ovulate. Just after ovulation, your BBT rises about half a degree to a whole degree Fahrenheit. If you end up getting pregnant, it will likely continue to rise even more. So if your BBT doesn’t fall back down to your baseline by the time of your expected period, there’s a chance you could be pregnant.
Was this article helpful?
- Physiology, Ovulation And Basal Body Temperature – StatPearls – NCBI Bookshelf
- Detection of ovulation, a review of currently available methods – PMC
- Urinary Luteinizing Hormone Tests: Which Concentration Threshold Best Predicts Ovulation? – PMC
- Timed intercourse for couples trying to conceive – Gibbons, T – 2023 | Cochrane Library
- Fecundity in relation to use of fertility awareness indicators – FertStart
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