Understanding BBT: A simple guide to our body's natural signals
If you use a menstrual tracking app to track your cycles or if you are thinking about planning a family, chances are, you may have encountered the phrase BBT. But what does this mean and did you know this nifty method of tracking your body temperature, has many surprising benefits, from improving your chances of conceiving to identifying problems in your menstrual cycle. Intrigued…? Let me tell you more…
Tuning into your body’s natural indicators
Ever wondered how your body naturally signals where you are in your cycle? One of the simplest, science-backed ways to tune in is by tracking your basal body temperature (BBT).
BBT is your body’s lowest resting temperature, taken first thing in the morning. Whether you're trying to keep tabs on your fertility or just curious about your cycle, understanding your body’s natural rhythm can help you to;
Identify ovulation and pinpoint your most fertile days if you are trying to conceive
Spot early pregnancy signs based on temperature shifts
Gain better awareness of your cycle and hormonal patterns
How Does BBT Tracking Work?
Your BBT fluctuates throughout your menstrual cycle. Typically during your period and the days before ovulation, your temperatures are low. After ovulation, your BBT rises slightly due to increased progesterone levels and should remain higher for roughly 12-14 days, after which it may drop again signally the start of your next menstrual cycle. By monitoring this temperature shift with the BBT method, you can determine when ovulation has likely to have occurred. This is different to Ovulation Predictor kits ( OPK’s), which predict ovulation based on hormonal surges tested through urine, but does not confirm that ovulation definitely took place.
How to Measure BBT Accurately
To ensure an accurate reading of your basal body temperature (BBT), follow these easy steps:
Use a BBT thermometer that measures to two decimal places. It doesn’t need to be fancy, you can get one for under £8 on Amazon, but there are lots of options available that include features such as LED lit screens, quiet sound modes or syncs up to a BBT tracking app.
Take your temperature immediately upon waking, before talking or moving around.
Try to get at least three hours of uninterrupted sleep before measuring.
Measure at the same time each day for consistency.
Record your readings daily using printable BBT charts, which you can download here or use a fertility tracking app. There are many apps like Flo, or Natural Cycles, but I like Read my Body, due to its ease and privacy guidelines, for those concerned about the use of their health data.
Using BBT to Understand Ovulation and Fertility
Monitoring your basal body temperature (BBT) can help you identify your most fertile days by revealing the subtle shifts in your cycle. During the first half of your menstrual cycle, your temperature remains lower (around 35.9-36.4), then rises slightly after ovulation due to increased progesterone.(around 36.5 - 37.0), and stays in the higher ranges until the end of your cycle and menstruation starts, where it drops again. If your BBT stays elevated for over 18 days, it could be an early sign of pregnancy.
This method, often called natural family planning or fertility awareness method, can help you time intercourse when trying to conceive or, alternatively, avoid pregnancy by using protection on fertile days. While BBT tracking is a very useful tool, it’s important to remember that various factors can impact readings, so using it alongside other methods detailed in a later section can be helpful.
Are You Ready to Decode Your BBT and Take Charge of Your Fertility?
As a fertility acupuncturist, I help women interpret their BBT patterns, balance their cycles, and optimise their chances of conception.
What Affects Your BBT?
BBT is super sensitive, and several things can influence your readings:
😴🧛♀️ Sleep patterns - Not enough sleep or irregular sleep can impact your temperature. Ideally you want to have slept for at least 3-4 hrs uninterrupted, before taking your temperature.
🍸 Alcohol consumption - A few drinks the night before a reading may cause temperature fluctuations.
🦠🤒 Illness - Fevers or infections can throw off your BBT, often spiking high.
🧬🧠⚖️ Hormonal conditions - Conditions like hypothyroidism can cause fluctuations and below average low readings.
💊Medications - Certain drugs might affect your body's temperature regulation.
Can BBT Tracking Indicate Pregnancy VS NOT PREGNANT?
BBT tracking is a great tool, but many people combine it with other fertility signs to understand their cycle more clearly:
Cervical mucus monitoring – Your mucus becomes clear and stretchy before ovulation, signalling peak fertility. If you visibly can’t notice it, be aware of whether using toilet paper to wipes feels dry or glides easily. If you notice a lubricating, gliding feeling, this is highly likely to be fertile mucous.
Ovulation test kits – These detect hormonal surges in your urine to confirm when ovulation is approaching.
Cycle tracking apps – Many apps analyse past cycles to help predict fertile days with no additional data, but is most reliable when using it alongside tracking BBT and your cervical mucus.
A consistently high basal body temperature for more than 17 days could be an early pregnancy sign so maybe worth taking a pregnancy test.
Final Thoughts
BBT tracking is a simple yet powerful way to feel more in tune with your body’s natural rhythms. It helps you recognise ovulation patterns, gain deeper insight into your cycle, and even spot potential early pregnancy signs. By observing these subtle shifts, you’re not just tracking data, you’re honouring your body’s wisdom and learning to trust its natural signals.
That said, BBT tracking isn’t perfect. It only confirms ovulation after it happens, and factors like stress, sleep, and travel can sometimes affect readings. But with patience and consistency, it becomes easier to see meaningful patterns over time. Whether you’re trying to conceive or exploring a natural way to track your menstrual cycles, BBT offers an intuitive approach to reproductive health, whilst helping you deepen your connection with your body.
References:
Mayo Clinic: "Understanding Ovulation and Fertility Tracking"
American College of Obstetricians and Gynecologists (ACOG): "Methods of Natural Family Planning"
National Institutes of Health (NIH): "Hormonal Changes and Basal Body Temperature"