The Mortgage Interest Deduction

The mortgage interest deduction lets homeowners reduce their taxable income by the interest they pay on a qualifying mortgage. It is one of the most famous tax breaks in America — and one of the most misunderstood. For most homeowners today, it is worth far less than they assume, and for many it is worth nothing at all. Here is how it actually works.

How the deduction works

If you itemize deductions on your tax return, you can deduct the interest you paid during the year on mortgage debt used to buy, build or substantially improve your primary or secondary home. The deduction applies to interest on up to $750,000 of mortgage debt for married couples filing jointly (and single filers), or $375,000 for married couples filing separately. Debt above that limit does not generate deductible interest.

The mechanics are simple on the surface: you report the interest from the Form 1098 your lender sends each January, and it reduces your taxable income. The value of the deduction is that interest amount times your marginal tax rate. If you paid $12,000 in mortgage interest and you are in the 22% tax bracket, the deduction saves you up to $2,640 in federal tax — if you itemize.

The catch that most buyers miss

Here is the part nobody tells you at the closing table: the deduction only helps if you itemize, and most homeowners do not.

Every taxpayer gets a standard deduction — a flat amount you can subtract with no paperwork. For 2024 it is $14,600 for single filers and $29,200 for married couples (rising to $15,000 and $30,000 in 2025). You may either take the standard deduction or itemize, whichever is larger. You cannot do both.

To make itemizing worthwhile, your total itemized deductions — mortgage interest, plus the state and local tax (SALT) deduction capped at $10,000, plus charitable gifts and a few others — must exceed the standard deduction. A married couple needs over $29,200 of itemized deductions before the mortgage interest starts doing anything. With a $10,000 SALT cap and typical charitable giving, that means a large mortgage with a lot of interest.

Who still benefits

The 2017 Tax Cuts and Jobs Act roughly doubled the standard deduction and capped SALT at $10,000, which dramatically shrank the number of people who itemize. The deduction now mainly benefits:

• Large mortgages in high-tax states. A $700,000 loan in a high-property-tax state generates enough interest and state tax to clear the itemizing bar.
• Early in the loan. Interest is front-loaded, so the first years of a mortgage produce the largest interest deduction — exactly when the balance is highest.
• Homeowners who already itemize for other reasons, like large medical expenses or charitable giving. For them, mortgage interest is a bonus on top.

If you have a modest mortgage in a low-tax state, the odds are you take the standard deduction and the mortgage interest deduction is worth $0 to you.

A worked example

Say you are married, bought a $400,000 home with 20% down ($320,000 loan) at 6.5%. Your first-year interest is about $20,700.

Your itemized deductions might look like: $20,700 mortgage interest + $10,000 SALT (capped) + $2,000 charitable = $32,700. That clears the $29,200 standard deduction, so you itemize. The difference is about $3,500 more than the standard deduction, worth roughly $770 in the 22% bracket. Real, but modest — not the giant subsidy home-buying lore suggests.

Contrast that with a $200,000 home: first-year interest is about $10,300, plus $10,000 SALT and $2,000 charity = $22,300 — below the standard deduction. You would take the standard deduction and get zero benefit from your mortgage interest.

Why the deduction should not drive your purchase

The worst reason to buy a house is "for the tax deduction." Here is why: the deduction only returns a fraction of the interest you pay, and only if you itemize. Paying $20,000 in interest to save $2,600 in tax is not a profit — it is spending a dollar to get back 22 cents.

Think of the deduction, at most, as a small rebate on the cost of borrowing. It can make a home slightly cheaper, but it never makes a home a good deal by itself. The real drivers should be the actual cost of the home, the rate, and whether the monthly PITI fits your budget.

What qualifies and what does not

Not all mortgage interest is deductible. Qualified interest includes interest on acquisition debt — money used to buy, build or substantially improve a primary or second home — up to the $750,000 limit.

Interest that does not qualify includes:

• Home equity debt used for non-home purposes (paying off credit cards, vacations), under the post-2017 rules
• Interest on debt above the $750,000 cap
• Interest on a rental or investment property (that is handled on a different schedule)

If you use a home equity loan to build an addition, the interest may be deductible as acquisition debt. Use it to buy a car, and it is not. The purpose of the borrowed money, not the collateral, is what matters.

Frequently asked questions

Do I have to itemize to deduct mortgage interest?

Yes. If your itemized deductions are below the standard deduction, you take the standard deduction and get no separate mortgage-interest benefit.

What is the limit on the mortgage interest deduction?

Interest on up to $750,000 of qualifying mortgage debt for single filers and married couples filing jointly; $375,000 for married filing separately.

Is the deduction the same as the SALT deduction?

No. Mortgage interest is its own deduction. SALT — state and local taxes, including property tax — is a separate deduction capped at $10,000.

Does refinancing change my deduction?

It can. Interest is deductible only on debt up to the cap, and on the portion used for the home. Cash-out refinance proceeds spent on non-home expenses are generally not deductible.

Focus on the real cost of borrowing — see your total interest for any loan with the HomeMath mortgage calculator.