http://www.cnbc.com/2016/12/01/heads-up-homeowners-mortgage-interest-deduction-on-trumps-chopping-block.html

The mortgage interest deduction is already capped at loans up to $1 million if you're married and filing jointly, and at $500,000 if you file separately. That said, the median price of a home in the United States is just more than $200,000, so not a lot of people make it to that cap. The vast majority of those who do benefit earn more than $100,000 a year and are not the most cost-burdened homeowners.

The deduction is very popular, but it benefits far fewer taxpayers than one might think. The current homeownership rate is around 62 percent, but of those homeowners, one-third do not have a mortgage. They own their homes outright, so the deduction would not apply to them.

Some homeowners, mainly middle- and lower-income families either don't pay federal income taxes or don't itemize, so the deduction wouldn't apply to them either. Only about 40 million (or 22.5 percent) of the 173 million households in the U.S. benefit from the mortgage interest deduction, according to the Tax Policy Center.

For those who do itemize, here's how the math works: Let's say you have a $500,000 30-year-fixed mortgage at 4.5 percent, and you're in the 33 percent tax bracket. In the first year of your loan, the deduction saves you just more than $10,000 in taxes.

If the Trump administration caps deductions at even $100,000, as Mnuchin suggested, that would not hit most borrowers because on that $500,000 (which is more than most loans in general) the total annual interest payment was about $23,000. Granted, homeowners may have other deductions, medical expenses, charitable, religious or otherwise, but most would not make it to $100,000 even with the mortgage.

Despite the small number of borrowers a cap would affect, real estate industry leaders oppose any changes, especially in an environment where they are trying to convince young millennials that a home is a good investment.