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Analysts often add up tax expenditures to estimate an aggregate cost, but those tallies are inaccurate because they ignore interactions among provisions. We estimate that interactions raise the cost of nonbusiness tax expenditures by 5 to 8 percent, depending on whether an AMT patch is in effect. In 2007, these tax expenditures totaled about $750 billion5.5 percent of GDP. While tax expenditures benefit taxpayers in all income groups, high-income households gain more relative to income than low-income ones. Although the AMT eliminates some tax preferences, it increases overall tax expenditures because most AMT taxpayers face higher marginal tax rates.