Although everyone seems to be taught that the normal human body temperature is 98.6 degrees Fahrenheit, in reality, “normal” has a range. In fact, a person’s actual measured temperature is rarely exactly 98.6 degrees Fahrenheit. One reason for this has to do with how the old standard was calculated: using an oral mercury thermometer and basing the results on a small human sampling.

Gone are the days of putting a thermometer under one’s tongue for five to ten minutes. Today’s thermometers are more sophisticated, accurate, and faster. Thus researchers believe that, based on better data—and more people tested—normal body temperatures measured orally range from 97.5 to 98.8, with about 1 in 20 people having a bit higher or lower normal temperatures. These numbers change throughout the day, too, varying from 1 to 2 degrees (on the average, reaching a low at about 2 a.m. to 4 a.m., and a high twelve hours later). An even more accurate representation of a body’s temperature is to measure the core temperature, or the actual temperature inside the body, usually by using a rectal or inner-ear (tympanic) thermometer.