Basal body temperature (BBT) is your body's temperature at rest, like when you first wake up in the morning. Your reproductive hormones have a measurable impact on your temperature (1,2). A BBT thermometer is more sensitive than a regular household thermometer, and measures temperature more precisely.
Tracking your BBT is an easy way to get an idea of if and when you're ovulating. Using it as a part of fertility awareness requires additional symptom tracking, and not every Fertility Awareness Method (FAM) is right for every body — talk to your healthcare provider if you're interested in using a FAM for contraception.
Why track basal body temperature?
Tracking BBT with Clue can help make your predictions more accurate. BBT is used by Clue to assess when ovulation has occurred. However, BBT alone cannot predict when ovulation will occur in the future.
BBT is slightly lower in the follicular phase (the first half of the menstrual cycle), and rises after ovulation and stays raised throughout the luteal phase (the second half of the menstrual cycle) (2,3). This rise in temperature happens in response to progesterone, which is released after ovulation occurs.