Understanding Basal Body Temperature: Why is it High or Low?


If you're trying to understand your fertility and increase your chances of getting pregnant, tracking your basal body temperature (BBT) is an incredibly useful tool. But what exactly is basal body temperature and what does it mean when you get high or low temperatures? Let’s find out!

Understanding Basal Body Temperature: Low BBT & High BBT

What Is Basal Body Temperature?

Basal body temperature is your body's temperature at complete rest, particularly upon waking up after a peaceful night's sleep. Consider it your body's internal thermostat, revealing important clues about your menstrual cycle and fertility health, and it’s so easy to track!

Ovulation BBT tips

Why Track Your Basal Body Temperature?

Tracking your BBT is your secret weapon in better understanding your menstrual cycle. You can identify your cycle’s pattern and confirm ovulation, by monitoring your daily temperature. Right before you ovulate, your BBT tends to be low. After ovulation, it rises and stays elevated until your next period due to progesterone being released. By charting these temperature shifts, you can determine your fertile window - the prime time for baby-making! The free Premom app, along with the Easy@Home smart basal thermometer, offers a convenient solution for tracking your BBT. The thermometer automatically syncs and charts your temperatures in the app, helping you identify your fertile window with ease.

BBT is also a natural and non-invasive method to track ovulation. It’s a great solution for anyone looking to dig deeper into their reproductive health. When combined with other fertility awareness methods like monitoring cervical mucus and using ovulation predictor kits it can help you decode your fertility puzzle.

What Is a Normal Basal Body Temperature?

While what is normal for one person may slightly differ for another, a normal basal body temperature typically ranges between 97.0°F (36.1°C) and 97.7°F (36.5°C) before ovulation. After ovulation, it increases by about 0.5°F (0.3°C) to 1°F (0.6°C) and remains elevated until the start of your next menstrual cycle; if you’re pregnant, it will remain elevated past your missed period.

Why Is Your Basal Body Temperature High?

A high BBT is often an indicator that ovulation has occurred. After you ovulate, the hormone progesterone is released, which causes a rise in body temperature. This increase in temperature can last throughout the second half of your cycle, also known as your luteal phase. If your BBT remains high for at least 18 days after ovulation, it may be a sign of pregnancy!

Causes of high BBT:

  • Successful ovulation
  • Pregnancy
  • Illness
  • Certain medications (fertility medications, hormonal supplements)
  • Poor sleep
  • Stress
  • Warm environment

Does High Basal Body Temperature Mean Pregnancy?

While a high BBT can be a promising sign that you may be pregnant, it is not a definitive indicator of pregnancy on its own. Many factors can cause your BBT to rise, so it's important to consider other early pregnancy symptoms and take a pregnancy test for confirmation.

Related: BBT Chart: Pregnant vs Not Pregnant

Can BBT Drop and Still Be Pregnant?

Yes, it's possible for your basal body temperature to drop and still be pregnant. In some cases, a temporary dip in temperature, known as an implantation dip, may occur around 6 to 10 days after ovulation. This can be followed by a rise in temperature again. Not all women experience an implantation dip and still get a big fat positive pregnancy test! So, if you don’t see it, don’t count yourself out just yet.

Why Is Your Basal Body Temperature Low?

A low BBT can be indicative that you’re still in your pre-ovulation phase, also known as your follicular phase.  During this time, your body is revving up to release an egg and the hormone estrogen is dominant.  In contrast to progesterone causing a temperature increase, estrogen promotes a lower temperature.

Low BBT can also be due to various factors, such as poor sleep, illness, stress, or certain medications. Additionally, hormonal imbalances, such as hypothyroidism or anovulation, can cause consistently low BBT readings. If you notice consistently low temperatures over several cycles, it's worth discussing with your healthcare provider to explore potential underlying causes.

Causes of low BBT:

  • Poor sleep
  • Illness
  • Stress
  • Certain medications (hormonal supplements)
  • Extreme weight loss
  • Hormonal imbalances
  • Cold environment

Can Low BBT Impact the Chances of Getting Pregnant?

When it comes to your journey towards conception, low BBT can have an impact on your chances of pregnancy. Consistently low basal body temperatures may indicate hormonal imbalances or other potential issues with ovulation, which can affect fertility. It could indicate insufficient thyroid hormone levels or low progesterone levels. Regardless, it's essential to address any underlying causes affecting your BBT and menstrual cycle to maximize your fertility and chances of conception.

Can Sunburn Affect BBT Readings?

Yes, sunburn can potentially affect your BBT readings. Excessive exposure to the sun can temporarily raise your body temperature, which may lead to inaccurate BBT measurements. To ensure accurate readings, it's best to avoid sunburn (sunscreen is your friend) and protect your beautiful skin from excessive sun exposure.

Does Alcohol Affect BBT Results?

Alcohol consumption can indeed impact your BBT readings. Alcohol is known to disrupt sleep patterns and affect body temperature regulation. It can lead to poor sleep quality, resulting in inaccurate BBT measurements. Therefore, it's advisable to limit excessive alcohol intake to ensure more reliable data.

Does Hypothyroidism Cause Low BBT?

Yes, hypothyroidism — a condition characterized by an underactive thyroid gland — can contribute to consistently low BBT readings. The thyroid gland plays a crucial role in regulating metabolism and body temperature. When it's not functioning optimally, it can lead to lower body temperatures. If you suspect you have hypothyroidism, reach out to your doctor to have testing done. We want to get those levels within normal range to give you the best chance of pregnancy!

Five common symptoms of hypothyroidism:

  1. Fatigue: Persistent fatigue and low energy levels can interfere with reproductive health and affect fertility.
  2. Irregular menstrual cycles: Hypothyroidism can cause menstrual irregularities, such as longer or heavier periods, or even absence of periods, which can make it challenging to conceive.
  3. Weight gain: Unexplained weight gain or difficulty losing weight can disrupt hormonal balance and hinder fertility.
  4. Cold intolerance: Sensitivity to cold temperatures may indicate an underactive thyroid, which can impact reproductive function.
  5. Dry skin and hair: Dry skin, brittle hair, and hair loss are common symptoms of hypothyroidism that can be associated with fertility issues.

Basal Body Temperature: Wrapping It Up

Understanding your basal body temperature and its fluctuations can provide valuable insights into your fertility and menstrual cycle. Remember, consistency is key!

If you’ve been following all the golden rules of BBT tracking, and your patterns just aren’t making sense, feel free to reach out to one of our fertility experts in Ask An Expert or meet virtually with a member of our medical team. We are here to support you every step of the way!



Steward K, Raja A. Physiology, Ovulation And Basal Body Temperature. [Updated 2022 Jul 18]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK546686/

Baker, F. C., Siboza, F., & Fuller, A. (2020). Temperature regulation in women: Effects of the menstrual cycle. Temperature, 7(3), 1–37. https://doi.org/10.1080/23328940.2020.1735927

Sunburn | nidirect. (2017, October 19). Www.nidirect.gov.uk. https://www.nidirect.gov.uk/conditions/sunburn#:~:text=skin%20getting%20hot.-

Su HW, Yi YC, Wei TY, Chang TC, Cheng CM. Detection of ovulation, a review of currently available methods. Bioeng Transl Med. 2017 May 16;2(3):238-246. doi: 10.1002/btm2.10058. PMID: 29313033; PMCID: PMC5689497.

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