Basal body temperature (BBT) is the lowest body temperature recorded during rest, typically measured in the morning before any physical activity. It can fluctuate slightly throughout the menstrual cycle, often rising after ovulation due to increased levels of the hormone progesterone. Tracking BBT can help individuals understand their fertility patterns. A consistent rise in BBT may indicate that ovulation has occurred, making it a useful tool for those trying to conceive or avoid pregnancy. Accurate measurement requires using a digital thermometer and recording temperatures daily for reliable results.