The way it works is:
-- foundation/company gives a grant of 80k/year to your host institution, earmarked to be used for your training.
-- institution pays: your health , disability, malpractice insurance etc.
-- instituion pays to you approx 45k in 'stipend' or salary
-- if you stay less than two years, all you pay is federal income tax (not too bad, you pay something like 6-8k per year in that salary range)
-- you allways have to pay state income tax (where applicable). This is usually another $500-2000 per year.
-- if you stay more than two years, you have to pay 'FICA' in addition to federal and income tax. This includes 'social security' (basic retirement benefit) and 'medicare' (basic medical insurance for the elderly).