Interest in a major reform of the individual income tax that would broaden the base and use the additional tax revenues to lower rates and/or reduce the deficit has increased. The President's Fiscal Commission, for example, proposed an individual income tax reform with three objectives: to broaden the base and lower the rates, to contribute to deficit reduction, and to maintain or increase the progressivity of the tax system. The Fiscal Commission, a bipartisan group, proposed a major revision that would eliminate or modify most tax expenditures. A congressional proposal from the 112 th Congress for income tax reform and base broadening was S. 727 , introduced by Senators Wyden, Begich, and Coats. One way to broaden the tax base is to eliminate or reduce tax expenditures, which have been in the tax code since the passage of the progressive income tax in 1913. An understanding of four complex issues surrounding tax expenditures is necessary for an informed debate over broadening the tax base. First, tax expenditures affect the economic behavior of taxpayers (efficiency effects). Second, changing tax expenditures will change the distribution of tax benefits and the distribution of after-tax income (equity effects). Third, changes to tax expenditures could change the administrative burdens on taxpayers and the Internal Revenue Service (IRS). Lastly, many tax expenditures are popular among taxpayers and voters. Each one of these issues presents challenges to broadening the tax base, which could be difficult to overcome. For FY2014, the year used in analyzing these provisions, individual income tax expenditures, which account for most of the potential base broadening provisions, are projected to total over $1.1 trillion. This amount is equivalent to 74% of the total FY2014 revenue from individual income taxes, and about 7% of GDP. If used for rate reduction alone, eliminating these tax expenditures could allow tax rates to be reduced by around 43%. For example, the top 39.6% tax rate could be reduced to about 23%. This additional tax revenue, however, is equivalent to about 6% to 9% of projected FY2014 individual income tax, and, consequently, would not allow for significant reductions in tax rates (about a one or two percentage point reduction, thus reducing the top 39.6% tax rate to 37%). Table 1 , therefore, divides tax expenditures into seven major categories: saving, business investment, consumption, owner-occupied housing (which is a combination of an investment choice and a consumption choice), labor supply, government programs (which in many cases would have no behavioral effects but are simply income transfers), and a category termed structural (which provides benefits based on family circumstances rather than affecting behavior). There are over 200 separate tax expenditures, but the cost is highly concentrated in a relatively small number. Concluding Remarks

The analysis in this report suggests there are impediments to base broadening by eliminating or reducing tax expenditures, because they are viewed as serving an important purpose, are important for distributional reasons, are technically difficult to change, or are broadly used by the public and quite popular. These specific tax expenditures account for 11% of the total revenue loss of all tax expenditures ($132.7 billion). These tax expenditures account for over 60% of the revenue loss of all tax expenditures. Given the barriers to eliminating or reducing most tax expenditures, it may prove difficult to gain more than $100 billion to $150 billion in additional tax revenues through base broadening. This amount could have a significant effect on reducing the FY2014 budget deficit—reducing the projected $345 billion deficit by 30% to 43%.
Congressional interest in a major reform of the individual income tax that would broaden the base and use the additional tax revenues to lower rates and/or reduce the deficit has increased. The President's Fiscal Commission, for example, proposed an individual income tax reform with three objectives: to broaden the base and lower the tax rate, to contribute to deficit reduction, and to maintain or increase the progressivity of the tax system. The Fiscal Commission proposed to broaden the tax base by eliminating or modifying most tax expenditures. One legislative proposal in the 112th Congress, S. 727, introduced by Senators Wyden, Begich, and Coats, would broaden the tax base by eliminating many tax expenditures and reduce tax rates.
One way to broaden the tax base is to eliminate or reduce tax expenditures, which have been in the tax code since the passage of the progressive income tax in 1913. An understanding of four complex issues surrounding tax expenditures is necessary for an informed debate over broadening the tax base. First, tax expenditures affect the economic behavior of taxpayers (efficiency effects). Second, changing tax expenditures will change the distribution of tax benefits, and the distribution of after-tax income (equity effects). Third, changes to tax expenditures could change the administrative burdens on taxpayers and the Internal Revenue Service (IRS). Lastly, many tax expenditures are popular among taxpayers and voters. Each one of these issues presents challenges to broadening the tax base, which could be difficult to overcome.
There are over 200 separate tax expenditures, which are projected to total over $1.1 trillion in FY2014. The revenue loss of all tax expenditures, however, is highly concentrated in a relatively small number—the largest 20 tax expenditures account for 90% of the total revenue loss of all tax expenditures. This amount is equivalent to 74% of the total FY2014 revenue from individual income taxes. If used for rate reduction alone, eliminating these tax expenditures could allow tax rates to be reduced by around 43%: for example, the top 39.6% tax rate could be reduced to approximately 23%.
When evaluating tax expenditures as potential base broadening provisions, it is useful to consider the general kinds of behaviors they affect or the general objectives in determining the feasibility of eliminating or modifying specific tax expenditures. Consequently, tax expenditures are divided into seven major categories: saving, business investment, consumption, owner-occupied housing (which is a combination of an investment choice and a consumption choice), labor supply, government programs (which in many cases would have no behavioral effects but are simply income transfers), and a category termed structural (which provides benefits based on family circumstances rather than affecting behavior).
The analysis in this report suggests there are impediments to base broadening by eliminating or reducing tax expenditures, because they are viewed as serving an important purpose, are important for distributional reasons, are technically difficult to change, or are broadly used by the public and quite popular. Given the barriers to eliminating or reducing most tax expenditures, it may prove difficult to gain more than $100 billion to $150 billion in additional tax revenues through base broadening. This amount could have a significant effect on reducing the FY2014 budget deficit—reducing the projected $345 billion deficit by 30% to 43%. This additional tax revenue, however, is equivalent to about 6% to 9% of projected FY2014 individual income tax revenue, and, consequently, would not allow for significant reductions in tax rates (about a one or two percentage point reduction for each bracket).