The study also found that if the goal was to prevent the new tax rates from hitting the poor and middle class, there would need to be a zero tax bracket and the highest individual tax rate would be capped just under 30 percent — lower than current law.
“To me, this exercise introduces a note of realism in how low income tax rates can go,” said Mark Mazur, director of the Tax Policy Center.
The study was a highly theoretical exercise, making the assumption that it would be possible, in one sweeping blow, to get rid of essentially all the deductions, tax credits and exclusions that are woven into the complex American tax code.
That puts a sort of boundary on what to expect out of tax reform — the lowest rates could possibly go if the goal is to remain revenue neutral.
But it is also extremely unlikely to happen as modeled; politicians have talked about changing or limiting specific tax breaks, not a wholesale elimination of every policy in the code.
Tax Policy Center analysts used three scenarios but stuck to a lowest corporate tax rate of about 26 percent.
That's a big reduction over today's rate of 35 percent, and in line with what House Speaker Paul D. Ryan (R-Wis.) recently suggested was a possible target. Earlier this week, Treasury Secretary Steven Mnuchin also said that Trump's goal of 15 percent might not be feasible.
“That's about as good as you can do,” Mazur said. The result backs up an analysis by the Joint Committee on Taxation from 2011, which found that the corporate tax rate could dip as low as 28 percent by eliminating tax breaks while remaining revenue neutral.
The Tax Policy Center researchers also examined how striking tax breaks could change how much individuals pay, modeling a change from the current seven tax brackets to three.
Their first finding was that by simply getting rid of all the current tax breaks, the tax rates could go as low as 6.1, 11 and 28 percent. But those rates would be highly regressive, hitting the poor and middle class the hardest while benefiting the rich.
Households in the lowest income quintile would pay $1,330 more in 2027 than under current law, while the top 1 percent of the income distribution would save $79,170. The top 0.1 percent of the income distribution would save close to $300,000 over current law.
By selectively preserving tax breaks that help lower-income people, including the earned income tax credit, the child tax credit, and the partial exclusion of Social Security benefits from tax, the effects became more equitable.
But when researchers prioritized making sure the new taxes weren't a big hit on the poor and middle class, they found that they needed four tax brackets, including a zero percent tax bracket on the low end and one at nearly 30 percent on the high end.
Trump's tax plan has proposed three tax brackets, of 10, 25, and 35 percent. Although the top rate of nearly 30 percent is lower than Trump's proposed rate, other differences exist between the two scenarios, and the effective tax rate would not be lower, according to the Tax Policy Center.
The analysis “illuminates the choices available to policymakers and demonstrates clearly that fiscally responsible tax reform is achievable,” the nonpartisan Peter G. Peterson Foundation, which funded the study, said in a statement.