Basal Body Temperature Charting: 3 Simple Steps to Get Started
Last week, I shared a blog post on how to track ovulation, and briefly introduced Basal Body Temperature (BBT) charting. If you’re trying to conceive, understanding when you ovulate can help you time intercourse correctly—and that’s where BBT charting comes in.
What Is Basal Body Temperature?
Your Basal Body Temperature is your body’s resting temperature. It changes slightly throughout the menstrual cycle due to hormonal fluctuations:
During the follicular phase, oestrogen is dominant, and BBT usually sits around 36°C
Around ovulation, there may be a slight dip in temperature
During the luteal phase, progesterone increases, raising your BBT slightly
If pregnancy occurs, BBT stays elevated; if not, it drops again before your period
What Does a BBT Chart Look Like?
A healthy BBT chart is typically biphasic, showing two distinct temperature ranges:
Before ovulation: lower temperatures (e.g. 36.2°C–36.3°C)
After ovulation: higher temperatures (e.g. 36.5°C and above)
You might also notice a slight dip around ovulation, followed by a sustained rise.
📉 If your chart doesn’t show a clear rise or takes several days to rise, you may not be ovulating—or ovulation may be delayed.
Even if your chart isn’t perfect, it can still provide valuable insight to your practitioner and help guide further investigations.
Why Is This Helpful?
When you track your BBT over several cycles, you’ll begin to identify your personal ovulation window.
Knowing your ovulation day allows you to better plan for conception. Since the egg only survives for 12–24 hours, it’s ideal for sperm to already be present in the fallopian tube.
Aim for intercourse every second day starting a few days prior to expected ovulation. On a chart, these days are often marked with a circle for guidance.
3 Simple Steps to Start BBT Charting
Step 1: Get the Right Thermometer
Buy a BBT-specific thermometer that measures to two decimal places.
Choose one that goes under the tongue for ease and accuracy.
Step 2: Take Your Temperature Every Morning
Measure your BBT immediately upon waking—before getting out of bed, talking, drinking water, or moving around.
Keep the thermometer within reach on your bedside table.
Step 3: Record and Track Your Results
Place the thermometer on the same side of your mouth each day.
Once it beeps, record your temperature to the decimal point.
You can use a paper chart or an app to track and visualise your cycle.
A Few Notes on Accuracy
BBT can be impacted by external factors, including:
Less than 3 hours of sleep
Disturbed or poor-quality sleep
Illness or fever
Alcohol, drugs, or medication
High stress
Electric blankets or external heat sources
📌 Note down anything that may affect your daily reading so you can interpret the chart more accurately later.
If you’d like help getting started with BBT tracking, or you’ve already started and want support deciphering your chart, please get in touch with us at Sydney Natural Fertility. We’re here to guide you on your fertility journey with knowledge and compassion.
Reference
Steward, K., & Raja, A. (2023). Physiology, Ovulation and Basal Body Temperature. In StatPearls. Read here.
