My norm seems to be between 100.0 to 100.4
The book by Dr. Broda Barnes basis a LOT of weight on basal (at rest) body temp.
I believe he said that anyone outside of 97.8 to 98.2 either has hypo (lower) or Hyper (higher) thyroid issues.
Basal body temp is with a mercury thermometer immediately after you initially wake up in the morning. Do NOTHING else and put the thermometer under your arm for 10 minutes. Nothing less and do NOT use those automatic electronic thermometers because they do not stabilize enough. You need several minutes preferably 10 minutes.
This makes total sense to me. Body temp is simply measuring the furnace and the engine of you body. And since Thyroid controls virtually every single aspect of the metabolism and the rate of the furnace burning. Measuring temp is as good a gauge as anything.
he further advocates treating and medicating until the symptoms go away. But uses basal body temp as a gauge to know when you are getting close to the right thyroid level.
My wifes body temp is barely ever above 97.0 to maybe 97.4.
For women you also have to be aware of where in the menstrual cycle you are. I have read two opposing thoughts on this. One stated only during the 1st couple days after you start your period. The other said after the first couple days. So maybe the best idea is to record the temps for several days or even every day for a month.
Dr's seem to pooh-pooh this. They simply shrug off low temps and say that "well 98.6 is just an average so a certain number of people will have temps under that and others will have it over it. So they simply dismiss it.
Notice however that the temp range listed above is well BELOW 98.6. By a half to a full degree.
My temperature fluctuates constantly. It is normally in the upper 96s or lower 97s. It tends to go up into the 98s after I eat, workout, after a hot shower and when I am stressed. My temperature is also affected by the weather outside.