Q: Does the mortgage-interest deduction apply to your second home as well as to your primary residence?

S.R.M., New York City

A: Yes, at least for 2012. But nobody knows what will happen to this and many other major tax laws after this year.

It seems clear that Congress won't eliminate the entire mortgage-interest deduction, no matter what happens in the November elections. But it's too soon to know whether lawmakers will impose significant new limits on the mortgage-interest deduction, including changing the rules for second homes.

Here are the basics:

The mortgage-interest deduction is available only to homeowners who itemize their deductions on their federal income-tax return.

The general rule is that home mortgage interest is "any interest you pay on a loan secured by your home (main home or a second home)," the Internal Revenue Service says in Publication 936, available on the IRS website (www.irs.gov).

A home includes "a house, condominium, cooperative, mobile home, house trailer, boat or similar property that has sleeping, cooking and toilet facilities," the IRS publication says.

Homeowners typically can deduct mortgage interest they pay on mortgage debt of as much as $1 million, according to the National Association of Realtors. (The limit is $500,000 if you're married and filing separately.)

Interest on up to $100,000 of debt on home-equity loans or lines of credit also typically qualifies for the deduction. (The limit is half that amount if you're married and filing separately.)

As with so many tax laws, there are many additional wrinkles and complexities, such as a home that a taxpayer rents out to someone else. Those are subjects for another day. If you're interested, read the IRS publication—and you may also need to check with a reliable tax pro.

Write to Tom Herman at tom.herman@wsj.com
