Why it's done

Basal body temperature can be used as a way to predict fertility or as a part of a method of contraception, by helping you gauge the best days to have or avoid unprotected sex.

Tracking your basal body temperature for either fertility or contraception is inexpensive and doesn't have any side effects. Some women may choose to use the basal body temperature method for religious reasons.

The basal body temperature method can also be used to detect pregnancy. Following ovulation, a rise in basal body temperature that lasts for 18 or more days may be an early indicator of pregnancy.

The basal body temperature method is often combined with the cervical mucus method of natural family planning, where you keep track of cervical secretions throughout the course of a menstrual cycle. You might also use an electronic fertility monitor to measure hormone levels in your urine, which can tell you which days you're fertile. This combination of approaches is sometimes referred to as the symptothermal or symptohormonal method.