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Donald Trump's plans to overhaul the U.S. tax system would benefit American expats abroad by lowering their overall tax bill, a wealth planning expert told CNBC on Friday. Kurt Rademacher, a partner at law firm Butler Snow, who specialists in ultra-high net worth families, told CNBC's "Squawk Box" that Trump's tax plans could reduce the headline tax rate and also eliminate the estate tax that currently applied to worldwide assets. The top federal rate of the estate tax currently sits at 40 percent, with estates worth less than $5.45 million exempt for the tax, according to the Internal Revenue Service (IRS).

"The tax bill for expats residing abroad would be reduced just as it would be if they remained in the United States," said Rademacher, adding that Trump had not yet said if he planned to amend existing tax rules on individual foreign earnings.

Tax-rule changes in the U.S. impact Americans living outside the country because the U.S. has an unusual "extraterritorial" tax system. U.S. citizens are taxed in the U.S. on their worldwide income no matter where they are based, although, according to the IRS website, expats could exclude a certain amount of their foreign earnings, adjusted annually for inflation, from their worldwide taxable income; for 2015, that amount was $100,800. They could also exclude or deduct certain sums related to foreign housing.

The system is at odds with those of most other countries, which allow their citizens to be taxed in their country of residence, with some restrictions.

On the campaign trail, Trump proposed major changes to individual tax rates, including reducing the seven federal tax brackets to three, with rates of 12 percent, 25 percent and 33 percent. He also proposed repealing the alternative minimum tax and the estate tax.

Tax experts estimated that a taxpayer in the U.S. who made $48,000-$83,000 a year would save about $1,000 under Trump's proposed plans, while people making $3.7 million or more annually would receive $1 million in annual tax savings. "Trump's theory, of course, is that these tax cuts that benefit mostly the wealthy individuals, and in some cases large corporations, would generate additional jobs and growth that would fund the economy and fuel changes for people who feel left out," Rademacher explained of changes that appeared to be weighted in favor of the wealthy.

Trump also pledged to cut corporate tax rates and offer a one-time break to U.S. companies that hold hundreds of billions of dollars in profits overseas to reduce their U.S. tax bill.