I can't tell you much about how they figure out the dosage, but I can tell you that my son's Florinef dose has changed over the years. He started at 0.2mg once daily when he was diagnosed at the age of 2 months, increased to 0.3mg at 15mo old, back to 0.2mg at 21mo old, down to alternating 0.1mg on odd dates & 0.2mg on even dates at (?)8yrs old, up to 0.2mg every day at 14yrs old. His labs & bone age have been well controled over the years, until he started puberty, but we seem to have him back on track again (at least for the time being.)