By: David J. Herzig
The Trump and Republican tax plans have circled around the idea of repealing the mortgage interest deduction. Although I’m not convinced it will happen (see e.g., Treasury Secretary Mnuchin’s remarks). The mere threat of the repeal has garnered a fair amount of attention.
For example, the other day this chart was making its rounds on twitter.
I have not verified the methodology of the chart or the data. I interpret that the chart examines (in absolute numbers) how many mortgages exist at $1,000,000. The implicit conclusion of the chart is that homeowners in states like D.C., Hawai’i, California and New York have the most at stake in retaining the deduction.
Because there seems to be evidence that the mortgage interest deduction contributes to housing inflation. Back in 2011 the Senate held hearings on incentives for homeownership.  It has been suggested that the elimination of the deduction will drop home prices between 2 and 13% with significant regional differences.  So, if the mortgage interest deduction is eliminated, then the aforementioned states might have numerous problems, including a smaller property tax base.
What exactly is the Mortgage Interest Deduction?