Basal body temperature fluctuates according to time of day and hormone level. Normal basal body temperature averages 36.8 degrees Celsius. 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 37 degrees Celsius, with an upper limit of 38 degrees Celsius. In recent years, several studies have challenged this value, claiming that average body temperature is 36.8 degrees Celsius, plus or minus 0.7 degrees, and the upper limit is 37.7 degrees Celsius.
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.
Normal basal body temperature is typically below 98 degrees Fahrenheit before ovulation and rises above 36.7 degrees Celsius 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.
In addition to hormones, other factors affect basal body temperature. Infection, air temperature, medication and fluid consumption can raise or lower basal body temperature.