How can basal body temperature help identify ovulation?

Basal body temperature (BBT) is a key component of fertility awareness techniques used to predict the fertile phase of the menstrual cycle.

By taking her temperature daily, a woman can detect a slight increase in her basal body temperature that signals ovulation has occurred. This method is most effective when combined with other indicators, such as keeping a calendar record of the cycle and observing changes in the constitution of cervical mucus discharge.

Because ovulation typically occurs at mid-cycle, identifying these physical signs helps a woman determine her most fertile period—approximately six days—during which she may choose to avoid sexual intercourse to prevent pregnancy. The effectiveness of this approach relies heavily on a regular menstrual cycle, as well as significant training and motivation, as the date of ovulation can vary unexpectedly even in women who are typically regular.1