@marcschare - nope.....
let x = unearned income (which by definition does not include social security) - see lines 1-8 of form 8960 for the specific items.
let y = total income, which is Line 11 of Form 1040 (by definition this does include the taxable portion of social security) - see line 13 of Form 8960 for the unusual situations where AGI has to be adjusted. But for most AGI on Line 11 of Form 1040 is what is used to define 'total income'
let z = the income that is subject to NIIT
the IRS website is simply stating that even though social security is unearned income, it is excldued from x; it is not stating it is excluded from y.
z = min((y-200000),x)
so z*3.8% is the tax
