One of the common challenges with natural conception is failing to detect when ovulation occurs, thus missing that small opportune moment for conception to occur. The Body Basal Temperature (BBT) chart is a useful tool infertility, as it is an accurate method of detecting ovulation and monitoring hormone levels. In this article, I want to help women identify when ovulation occurs using a simple and cheap object: the thermometer.

Did you know that the BBT chart was discovered by a German Catholic priest? In 1935, a German priest named Wilhelm Hillebrand conducted an observational research to identify when ovulation occurred using monthly temperature cycles. This research was inspired as a natural contraceptive approach to the rising number of unwanted pregnancies in his parish. He recruited 21 women, of which their temperatures were recorded on a daily basis. Hillebrand noticed that these cycles showed biphasic temperatures and allowed women to identify when in their cycle they had ovulated, and thus showing a pattern of when ovulation occurs. This ultimately was used as a successful method of birth control in his parish. Ironically, the BBT chart is now used by women to assist in natural conception.

Here is a sample chart below of what an ideal / stable BBT chart should look:

A brief explanation of the BBT Chart

As mentioned before, the BBT chart is biphasic, where there is a distinct temperature rise of 0.2 ℃ from day 13 to day 14. The biphasic chart reflects the dominance of either Oestrogen or Progesterone levels. The follicular phase, or the oestrogen dominant phase, occurs in the first half of the cycle (i.e. day 1 to 13) and the ideal temperature should sit at 36.5 ℃. The luteal phase, or the progesterone dominant phase, occurs from day 14 until day 28. For an optimal pregnancy, the temperature for the luteal phase should be 36.7 ℃ and this phase should last for roughly 12 days.

How do I identify ovulation?

When looking at the above chart, ovulation has occurred the day there is a temperature increase of 0.2 ℃, i.e. day 14. The process of ovulation is when the corpus luteum (otherwise known as the egg) is released from the ovary, causing a rise in progesterone, which ultimately increases the BBT. Prior to this, fertile mucus should be noticeable, which is often described as egg-white in consistency and colour. Note that the days are charted according to the menstrual cycle, and not calendar dates. Day 1 is the first day of the period, and day 28 is the last day of the cycle. Your cycle may differ, so please adjust the days accordingly.

What if your chart is unstable?

When charting your BBT, you may notice some variation in temperature, which can be due to external factors. This includes consumption of alcohol the night before, short or disturbed sleep, measuring the temperature at different times, going to bed late, and illness. If you observe temperature variations in your chart, and there is an explained reason for this, make sure you record it in your chart as well. If you notice your chart is highly unstable such as the one shown below, then this may be an indication that your lifestyle is impacting your hormones, and quite possibly, your fertility. Please seek medical advice if you and your partner have been trying naturally for roughly 6 months, as there may be other underlying health issues impacting fertility.

As mentioned in my previous article about the menstrual cycle, I touched on the four main contributing factors to varied menstrual cycles. These factors can also have a major impact on the BBT, and ultimately, fertility. For example:

  • Diet — eating at irregular intervals, overindulging in sweet foods, not having a balanced diet
  • Exercise — either too much or too little can stress the body
  • High stress levels — this is not necessarily referring to just work stress, but can also be emotional issues building up, having problems letting go, the pressure of having to always give your best at every activity; constant worrying
  • Sleep — this can include having trouble falling asleep, and/or waking up frequently throughout the night
  • Thyroid issues — hyperactive/hypoactive thyroids can significantly alter the BBT chart

How and when to track your cycle

Using a thermometer to track your hormones is easy. The only thing you have to worry about is remembering to measure your temperature every day: the only time of the day to measure your temperature is first thing in the morning before getting out of bed. All temperatures for the BBT is measured orally. If you are using a mercury thermometer, make sure you leave the thermometer under your tongue for 3 minutes. If using a digital thermometer, measure your temperature according to the manufacturer’s instruction. Remember, it is called the Body Basal Temperature, because you are measuring your temperature when your body is at baseline, i.e. at complete rest. The next step is to record your temperature, which can be recorded on a piece of paper or an app. I recommend Kindara for iPhone users, and OvuView for Android users. Alternatively, I have provided a BBT chart template, which you can download here.

Tip: Reset the mercury thermometer straight after measuring your temperature in the morning.

Digital or mercury?

Choosing the right thermometer to track your temperatures can be intimidating. There are currently so many different brands of thermometers to choose from (personally, I find that nothing beats a mercury thermometer, which is quite rare to find in pharmacies these days due to the potential risk in exposure to heavy metal poisoning if the thermometer breaks. However, if all appropriate safety measures are used, then the risk of breaking a mercury thermometer is quite low). When tracking BBT, accuracy is highly important. There is no point charting your temperatures if your thermometer is broken or unreliable. There have been countless times when I have had my patients track their temperatures using a newly bought digital thermometer from well recognised brands, only to find out a couple of months later that their thermometer was for some reason, inaccurate. To check the reliability of your digital thermometer, you can measure your temperature 3 times within 5 minutes at rest. If your thermometer is displaying a temperature variation of 0.2 ℃ or above during the 5 minutes, then this is an indication that your thermometer is unreliable. As a result, my recommendation for all of my fertility female patients is to use a mercury thermometer, which can be purchased online.

Happy charting!

In summary, to identify when ovulation occurs, look out for these factors: a rise in temperatures of 0.2 ℃, alongside the presence of fertile mucus. For some women, this rise may not be obvious, and if you find that you are struggling to interpret your BBT chart, I am more than happy to provide some feedback. You can email me your chart and any concerns via email:

Jeannie Kim is a registered acupuncturist based in Sydney and has a strong interest in fertility acupuncture. If you have any questions regarding this article, you can contact me via email: