< How it Works

Taking the Temprature

Use a digital or an analog thermometer. It should be labeled for the use of taking the Basal Body Temperature (BBT). Do not use an ear thermometer!

For readings in Celsius, the digital thermometer needs two decimal places. Chart your Celsius temperatures in 0.05 ºC steps and round accordingly.
Here are some examples for how to round your temperatures correctly when using Celsius as the temperature unit:

  • 36.62 ºC becomes 36.60 ºC
  • 36.63 ºC becomes 36.65 ºC
  • 36.67 ºC becomes 36.65 ºC
  • 36.68 ºC becomes 36.70 ºC

For Fahrenheit, one decimal will suffice. Chart Fahrenheit in 0.1 ºF steps, like 97.6 ºF, or 98.1 ºF.

If you wish to track two decimal places for Fahrenheit, you can do so, but we strongly advise against it. Both sets of rules state that you should round your Fahrenheit temperatures to the first decimal, essentially rendering the second decimal superfluous. If you still want to track two decimal places and not round your temperatures bear in mind that your temperatures might, in some cases, not meet certain thresholds, thus leading to incorrect evaluations, which in turn makes Lily's display of fertile and infertile phases and cycle predictions less accurate.

You can take your temperatures orally (wait 5 minutes with an analog thermometer), vaginally (wait 5 minutes with an analog thermometer), or rectally (wait 3 minutes when using an analog thermometer). Oral measurements can produce erratic temperature patterns, even when using advanced thermometers made specifically for taking temperatures orally, due to breathing through the mouth at night.

Taking the BBT outside your body (under your arms, for example) or in your ear is not recommended and will lead to false results.

Do not change the way of taking your temperatures during a cycle, wait for the next one to start.

Try to take your temperatures at roughly the same time every morning.

Exclude temperatures that might have been influenced due to interferences as fever, alcohol, staying up late, etc., to ensure an accurate evaluation.

Do not rely on temperatures alone. To ensure maximum safety, the sympto-thermal rules that Lily applies need to evaluate your cervical fluid quality as well.


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