Your basal body temperature (BBT) is the lowest temperature attained by your body at rest. It gives an idea of your body’s metabolism and of changes through your cycle, determined by your hormones.
Generally we expect a temperature of 36.2 to 36.5 celsius during the first half of your cycle and then an rise of about 0.2 to 0.5 celsius after ovulation. This creates a ‘biphasic’ pattern and the reading of this pattern from month to month provides a lot of useful information about your cycle and hormonal system.
Although not commonly used by conventional medicine due to the use of blood and urine tests, BBT charting provides us with information about the nature and stability of your cycle that cannot be discovered without doing tests everyday. This page is about how to take BBT readings and how to complete a chart.
Can I use it to know the best time to conceive?
BBT charting will show if, and when, you have ovulated during a cycle but it isn’t a good way to know during any one cycle when you will ovulate. For help with this your are better to reading the page about Ovulation Symptoms.
How do I take it?
Your BBT needs to be taken after at least three hours uninterrupted sleep and so is generally done when you first wake up. If you work shifts then the same applies but note down the time of day that you took your temperature on the chart. It is important that you take your temperature when you first wake up and before you get out of bed, to get consistent readings. Use a basal thermometer (available at chemists or online). You don’t need an expensive one but don’t necessarily buy the cheapest. The important factors are that it that is accurate and that it shows incremental degree changes of at least 1/10th of a degree celsius. Digital ones with built-in memory function can be useful if you take a reading in the middle of the night and don’t want to have to write it down there and then.
Put these readings onto your BBT chart in Celsius to show the temperature changes throughout your cycle. These fluctuations are caused by hormonal changes within your cycle and charting them will provide useful information. Over time the charts will allow me to build a good picture of how your system is working, where any instabilities lie and when are the best times for acupuncture. It is helpful to chart your temperature for a few months so you can see whether there’s a pattern to your cycle.
There are several pitfalls that can make the method less accurate. These include: not using the right equipment, taking your temperature at different times of the day, not recording the changes in BBT accurately, alcohol, illnesses and medication.
Marking the chart
1. Day 1 is the first morning you have your period. You can start marking the chart at any stage of your cycle. Note of the date at the top of the chart and start marking on the chart on the relevant day.
2. Put a dot in the centre of the square for your temperature and connect any dots on consecutive days with straight lines between them. If you miss a day, don’t join the dots.
3. At the bottom of the chart:
Bleeding (B): Put an F for flooding, H for heavy, M for moderate, L for light and S for spotting.
Cervical Mucus (M): Once you are familiar with the different types of cervical mucus, as described on the Ovulation Symptoms page, then mark accordingly.
Ovulation Prediction (Ov): If you are using an ovulation prediction test, mark it however your test describes it (e.g +ve at time of ovulation). Explain at bottom of sheet, if necessary.
Breast changes (BC): Again can be marked with any written explanations on the bottom of the page.
Abdominal pain (AP): Mark any cramping or discomfort during your cycle.
Signs and symptoms (S&S): Write anything of note that is not included in the list above.
4. Make any further notes that you need to on the bottom of the sheet (see below).
Other things to consider
What if I forget one day?
If you forget, or don’t take your temperature immediately on waking, make a note on the chart.
What if I am ill?
If you are ill, note your temperature and make a note on the chart.
Will different medications affect my temperature?
Painkillers, such as paracetamol, can reduce your temperature. If you are taking any medication please make note on chart what it is and when you took it.
Can anything else affect my temperature?
Drinking alcohol or sleeping in may increase your temperature. If either of these are the case please make note on the chart.
What should I do if my cycle lasts longer than 40 days?
Start a new sheet, make a note that it is a continuation and staple them together.
Can I use the chart to predict ovulation?
A chart, once completed, will show if and when you ovulated during that cycle but it is not a good way of predicting ovulation during that cycle. Cervical Mucus and Uterus Position changes (& ovulation sticks, if needed) are far more reliable for this purpose. For more information see the Ovulation Symptoms page.
Will I know if I am pregnant?
If you do become pregnant, your temperature will stay elevated after ovulation right through your pregnancy but you would need to be very familiar with your charts to know for sure.