On average, the 33.4 percent of New Jersey homeowners who file for the mortgage interest deduction on their taxes claim $13,215, according to the nonpartisan Tax Foundation after reviewing 2008 tax returns. That ranks New Jersey 10th among states in terms of the amount of mortgage deduction claimed. California, with $18, 876; Hawaii, with $16,730; and Nevada, with $15,502 are numbers one, two and three. The average for the country as a whole was $12,221. New Jersey ranked sixth for percentage of returns claiming the deduction. Maryland won the top spot in that category, with 37.9 percent of residents filing a tax deduction claim, for an average of $14,162.