What Is Normal Basal Body Temperature?

Basal body temperature fluctuates according to time of day and hormone level. Normal basal body temperature averages 98.2 degrees Fahrenheit. Changes in basal body temperature can be used to determine when ovulation occurs in the menstrual cycle.

Normal Temperature Range

• Historically, the standard for normal temperature is 98.6 degrees Fahrenheit, with an upper limit of 100.4 degrees Fahrenheit. In recent years, several studies have challenged this value, claiming that average body temperature is 98.2 degrees Fahrenheit, plus or minus 0.7 degrees Fahrenheit, and the upper limit is 99.9 degrees Fahrenheit.

Basal Body Temperature

• Body temperature fluctuates with the daily circadian cycle. Female hormones also cause body temperature to change throughout the menstrual cycle. Basal body temperature is the rise and fall of body temperature in response to hormone levels and time of day.

Highs and Lows

• Basal body temperature is at its lowest point around 6:00 a.m. and peaks between 4:00 p.m. and 6:00 p.m. During the menstrual cycle, the lowest temperature occurs on the day of ovulation and the highest temperature occurs during the second half of the cycle.

Ovulation

• Normal basal body temperature is typically below 98 degrees Fahrenheit before ovulation and rises above 98 degrees Fahrenheit after ovulation. A temperature drop of greater than 0.4 degrees Fahrenheit occurs during the 48 hours preceding ovulation. Basal body temperature rises following ovulation.

Environmental Factors

• In addition to hormones, other factors affect basal body temperature. Infection, air temperature, medication and fluid consumption can raise or lower basal body temperature.