Underarm (axillary) and forehead temperatures are considered to be the least accurate because they’re taken outside of the body rather than inside. These temperatures can be as much as a full degree lower than oral body temperature.

How many degrees do you add when you take a temperature under the arm?

An armpit (axillary) temperature is usually 0.5°F (0.3°C) to 1°F (0.6°C) lower than an oral temperature. A forehead (temporal) scanner is usually 0.5°F (0.3°C) to 1°F (0.6°C) lower than an oral temperature.

What is a fever under the arm?

The following thermometer readings generally indicate a fever: Rectal, ear or temporal artery temperature of 100.4 (38 C) or higher. Oral temperature of 100 F (37.8 C) or higher. Armpit temperature of 99 F (37.2 C) or higher.