How To BBT
Maybe you’ve heard of it, maybe you haven’t. BBT charting has been around for a while (since the 1930s) and is one of my favourite tools in the clinic to help clients with their fertility journeys and menstrual cycle health.
What is BBT?
BBT stands for basal body temperature. It is the lowest temperature your body reaches at rest. Think of it as your base-level temperature.
Throughout the day, as you move around, your body temperature fluctuates, making it unreliable for tracking ovulation.
Your BBT changes depending on where you are in your menstrual cycle.
Follicular phase (pre-ovulation phase): Oestrogen is dominant—it's a "cooler" hormone, keeping your BBT lower.
Ovulation: A beautiful little egg is released from the follicle, and that follicle starts producing progesterone.
Luteal phase (post-ovulation phase): Progesterone— a "warmer" hormone—raises your BBT. This is the "oven" turning on for the bun (baby).
Since progesterone is only produced after ovulation, tracking BBT is the only way to confirm if you have ovulated. If conception doesn’t occur, your BBT will drop, the oven will turn off, and your period will arrive.
Why track BBT?
The list of reasons is as long as my arm, but here’s why BBT charting is a fantastic tool:
Besides day 21 blood tests or ovulation-tracking scans with a fertility specialist, BBT tracking is the most accurate way to confirm ovulation.
Forget the pee sticks—yes, I know many of you are addicted to them! While they can complement BBT tracking in complex fertility cases, they aren’t reliable on their own.
BBT charting not only confirms ovulation but also provides insight into your follicular and luteal phases, helping pinpoint where you need support.
When should I track my BBT?
If it were up to me—all the damn time! It’s empowering.
Many women and menstruators don’t really understand their cycles beyond what they learned in Year 10 sex ed. But I get it, not everyone is a data nerd.
Here’s when I would ask clients to track BBT:
Trying to conceive (The most common reason)
If you’re trying to get pregnant, there’s no reason not to track. It’s the second-best way (after blood tests and scans) to confirm ovulation and gives insight into your oestrogen and progesterone levels—two key fertility hormones.
PCOS
Never-ending cycles?
Heavy bleeding?
Acne? Weight gain? Hair loss?
Tracking BBT can help spot patterns in ovulation attempts and successful ovulation.
PMDD (Premenstrual Dysphoric Disorder)
This debilitating condition occurs from ovulation to your period and is often linked to progesterone imbalances. BBT tracking can reveal temperature shifts in your luteal phase, helping guide next steps.
Perimenopause
Are you heading toward menopause?
Or are you just so burnt out that your symptoms mimic perimenopause?
BBT tracking helps distinguish between the two.
Recurrent miscarriage
I’m so sorry if this has been your experience. There are many reasons for recurrent miscarriage, and ruling out progesterone issues via BBT tracking can help you regain a sense of control in an unpredictable situation.
Missing periods
PCOS?
Polycystic ovaries? (Yes, these are different!)
Stress? Under-eating? Other hormonal imbalances?
BBT tracking can provide clues.
Natural contraception
🚨 DO NOT ATTEMPT THIS WITHOUT SUPERVISION! 🚨
There are so many variables. I do not recommend doing this alone. Your charts need to be supervised by a trained specialist.
Also—BBT charting does not protect against STIs.
How do I track BBT?
What you’ll need:
A digital thermometer (measures to one decimal place, e.g. 36.1°C). Bonus points if it saves your last reading.
An app—I recommend Fertility Friend to log your data.
How to take your BBT:
1️⃣ Keep your thermometer on your bedside table.
2️⃣ As soon as you wake up, before moving, drinking, or talking, take your temperature.
3️⃣ Try to take it at the same time every morning (yes, even on weekends).
⭐ Key guidelines for accuracy:
No movement before taking your temp—just grab the thermometer and pop it in your mouth.
No drinking or talking beforehand.
At least 3 hours of solid sleep before waking.
If your sleep is interrupted (e.g., your partner wakes you up at 5 am), take your temperature then instead of waiting for your usual wake-up time.
Life isn’t perfect—if something throws off your reading, just log it in the app. I can work around it!
How do I know I’m ovulating?
BBT charting takes some skill to interpret. Most of my clients simply log their temps, and I go over the data with them. Over time, many start recognising patterns themselves—some even run into appointments saying, "Look! I’ve ovulated!" 🤩
To identify ovulation, at least three full months of tracking is ideal, especially for those with irregular cycles (looking at you, PCOSers!).
Starting early in your fertility journey is super helpful. And yes, I have favourites—those who walk into their first appointment already charting? You. You’re my favourites.
Nah, just kidding. My favourites are my herb-taking clients. 😉
What can affect BBT charts?
Lots of things, including:
✅ Illness or fever
✅ Stress (surprise, surprise!)
✅ Shift work (sorry, nurses!)
✅ Interrupted sleep (parents, I see you!)
✅ PMDD-related oversleeping
✅ Alcohol (please cut back, or quit altogether if needed!)
✅ Travel and time zone changes
✅ Certain medications
BBT tracking feels too hard! Help!
If manually tracking feels overwhelming, consider investing in a Tempdrop. This amazing wearable device automatically records your BBT and syncs to its app (I still recommend Fertility Friend for the best charts).
And because I love you all, here’s 15% off! 🎉
What next?
If you want help with BBT charting or need me to review your charts, book in for a consult and treatment.
Let me help you master this awesome tool!
I look forward to seeing you in the clinic.
x Dr Alice
Written with the help of AI - I needed some help this blog. If there are spelling mistakes, blame Chat x
The information provided in this blog is for educational and informational purposes only and is not intended as medical advice. It should not replace consultation with a qualified healthcare professional. If you have endometriosis or any other health concerns, please seek guidance from your doctor, specialist, or a licensed Chinese Medicine practitioner.