Americans at all levels of income would save an average of $1,600 on their 2018 taxes if a Republican tax overhaul plan becomes law, according to an analysis published Friday by a tax watchdog group.

But 12 percent of taxpayers, many of them making between $150,000 and $300,000, could get hit with a tax increase averaging $1,800 on their 2018 return, mainly due to the repeal of most itemized deductions.

In general, the bigger your income, the more you would benefit from the tax changes, according to the analysis by the Tax Policy Center, a a Washington, D.C. not-for-profit think tank sponsored by the Brookings Institution and the Urban Institute.

The top 1 percent of earners, for instance, would see an 8.5 percent savings between 2018 and 2027. Those at the bottom 5th percentile of income, meanwhile, would see only a 0.5 percent to 1.2 percent savings over the same period, the report says.

The analysis comes just days after Republicans unveiled their blueprint for the sweeping overhaul, which they call the "Unified Framework for Fixing Our Broken Tax Code"

The GOP plan reduces the number of tax rates to three, nearly doubles the standard deduction, and makes more people eligible for child- and adult-care tax credits.

It also eliminates most other deductions, including those for state and local income taxes, but keeps deductions for mortgage interest and charitable contributions. The plan also eliminates the alternative minimum tax, or AMT, and the estate tax.

Over time, about a quarter of taxpayers would see their income taxes rise by 2027. While those making less than about $150,000 would get an average tax cut of 0.5 percent or less, those making between $150,000 and $300,000 would pay, on average, $800 more.

"The number of taxpayers with a tax increase rises over time," the report said. "This is because the plan would replace personal exemptions, which are indexed for inflation, with additional credits for children and non-child dependents that are not indexed for inflation."

Rising tax brackets, based on inflation, also could make more people vulnerable to tax increases, the report notes.

The analysis acknowledged that its estimates were very rough. Researchers were able to use figures from the plan—such as the three new tax rates of 12, 25 and 35 percent—but had to make assumptions about the brackets at which those rates would begin. 

Researchers used the same brackets outlined in a 2016 Republican plan, which folded the current 10 percent and 15 percent brackets into the new 12 percent bracket; the 25, 28, and 33 percent brackets into the new 25 percent bracket; and the 35 and 39.6 percent brackets into the new 35 percent bracket.

The plan would cost the U.S. $2.4 trillion over the first 10 years and $3.2 trillion over the second decade, absent any other tax changes. Much of that change in revenue would be due to proposed reductions in corporate taxes; $2.6 trillion would be lost in the first 10 years alone.

Cuts in individual taxes would trim another $980 billion in revenues; $240 billion of that would come from the elimination of the federal estate tax.