This exercise is a structured analysis to understand the implications that repealing tax expenditures would have for the overall federal tax system. The baseline tax law for the calculations in this exercise is the law in effect before enactment of the Tax Cuts and Jobs Act (essentially the Tax Code in effect for much of 2017).
In part 1 of this exercise, TPC estimates the revenue and distributional effects of proposals that would eliminate almost all income tax expenditures to lower individual and corporate tax rates and maintain long-run revenue neutrality for the federal tax system. The results of Part 1 show that individual and corporate income tax rates could be substantially reduced while meeting the dual constraints of long-run revenue neutrality and maintaining the distributional consequences of the current tax system.
Part 2 of this exercise restores five groups of tax expenditures and calculates the income tax rates necessary to maintain long-run revenue neutrality. This portion of the exercise also illustrates a drawback of considering tax expenditures in isolation: that approach ignores interaction effects between tax expenditures.
Part 3 of this exercise restores seven groups of the remaining tax expenditures and calculates the income tax rates necessary to maintain long-run revenue neutrality. The rationale for adding tax expenditures (or tax expenditure groups) back one by one is to illustrate the "tax rate price" associated with the tax expenditures.