However, taxpayers should note that Code Sec. 1411 is to follow normal income tax rules (i.e. rules that a tax lawyer or accountant might refer to as tax rules under chapter one of the Internal Revenue Code), so for ease of calculation, what is exempted from the regular income tax, such as tax-exempted mutual bonds, are also excluded from the NII sum.

FORBES: New Taxes and New Terms: How to calculate Net Investment Income under the New 3.8% Medicare Surtax