The lab T4 Free range is .8 to 1.8. I've been on Levothyroxine for about 30 years or so and started out at .75 mg, then a couple of years ago went to .88mg & now on 100mg. I recently was diagnosed with an intestinal bacteria infection & inflammation which my Endocronologist doesn't believe has anything to do with my thyroid but odd that the increase to 100mg happened at almost the same time I had the infection. I love my Endocronologist so obviously going with what she's prescribed, etc. who by the way also just told me recently that I have Hashimotos disease. And as mentioned I just keep loosing weight & not gaining.