 [ Symptoms ] do you add a degree whentaking tempture under arm [ Disease ] the average normal temperature under the arm 98 7 axillary is about one degree less than the mouth 98 6 and about two degrees less than the rectal temperature 99 6 keep in mind that these are just average temperatures based on a poorly controlled study using inaccurate thermometers done over a hundred years ago we still adhere to it even though we now know the average is slightly different temperatures also vary by the time of day lower in the morning higher in the evening if you are transmitting information to a medical provider you do not have to add or substract a degree all you need to do is say the temperature was 99 8 under the arm  let the medical provider make the adjustments