What is basal body temperature and how do I track it?

Bottom lineBasal body temperature (BBT) is your resting temperature taken first thing each morning before getting up; it rises about 0.3 to 0.6°C after ovulation due to progesterone and stays up until your period, confirming ovulation happened. Use a basal thermometer at the same time daily and track the trend over cycles; BBT confirms ovulation but can't predict it in advance, so pair it with cervical mucus or LH kits.

Basal body temperature (BBT) is your body's resting temperature, taken first thing in the morning before you get up. Tracking it helps confirm ovulation and learn your cycle pattern.

How it works

• Before ovulation, BBT is lower
• After ovulation, progesterone raises it by about 0.3 to 0.6°C (0.5 to 1°F)
• The temperature stays higher until your next period

A sustained rise confirms that ovulation has already happened.

How to track it

1. Use a basal thermometer (more precise than a regular one)
2. Take your temperature at the same time each morning, before getting out of bed, talking, or drinking
3. Record it daily and look for the sustained shift
4. Track over several cycles to see your pattern

What it can and can't do

• Can: confirm ovulation occurred, reveal your luteal phase length, show your pattern over time
• Can't: predict ovulation in advance (the rise comes after), which is why it pairs well with cervical mucus or LH kits for timing the fertile window

What can throw it off

Illness, poor sleep, alcohol, and shift work can all skew a reading, so look at the trend, not one day.

See how do I know when I'm ovulating and ovulation symptoms.

Femora lets you log BBT alongside other signs so the post-ovulation shift is easy to see.