How to chart your ovulation – Part 6

How to chart your Basal Body Temperature – BBT.

Main things to remember:

  • Record your basal body temperature (BBT) at the same time each morning (or as close to the same time as possible).
  • Record your BBT immediately on waking before getting up out of bed.
  • Use a digital thermometer which records to 2 decimal places (ovulation thermometer). One like the picture below is perfect.
  • Enter the recorded temperature into your fertility app or on your paper fertility chart.


What is an Ovulation Thermometer?

An ovulation thermometer is one that records to decimal places. This is important as the change in body temperature before and after ovulation is very small and may not be detected with a thermometer that reads to just 1 decimal place. A good digital ovulation thermometer will give you a quick reading and will beep when it has finished. It may also have a memory function and store your last body temperature. You can buy your ovulation thermometer for less than £5 on Amazon.


A complete guide to charting your BBT.

  • Record your BBT first thing in the morning before getting out of bed. Any movement can start to increase your BBT and affect the results.
  • Record your BBT at the same time each day ideally around 6-7am. As 8am approaches your BBT will naturally start to increase as your body is warming itself ready for the day.
  • You will need to have had at least 3-4 hours of sleep for an accurate reading.
  • Keep your ovulation thermometer next to your bed so you can locate it quickly.
  • f you are taking oral temperatures then keep your mouth closed for 3 minutes before placing the thermometer in the mouth. This will ensure that mouth breathing or a cold bedroom will not affect the results. Place the thermometer under the tongue to the back of the mouth and wait for the beep.
  • If you are taking vaginal or anal temperatures then ensure that the thermometer is thoroughly cleaned after each use to ensure no bacteria is introduced.
  • Stick to the same method of recording your temperature throughout your cycle (oral, vaginal or anal).
  • Input your recorded temperature into your phone app or on your paper chart straight away to avoid forgetting and missing a temperature.
  • Record the time you have taken your temperature if it is different than the time you usually take it. Recording a temperature at different times may affect the clarity of your chart.

Note on your chart if you are feeling unwell, had disturbed sleep or a late night or if you have drank alcohol the night before. All of these things can increase your BBT and will affect your chart. You can disregard any temperatures that are high for these reasons. More on this below.


Factors which can affect your temperatures and your chart:

  • A fever, an illness or infection, sore throat, cold, flu.
  • Waking later than usual
  • Drinking alcohol
  • Sleep disturbances – meaning you had less than 3-4 hours of solid sleep
  • Travel and jet lag or a sudden change in climate
  • Breast feeding
  • Certain drugs and medications.
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