The mortgage interest deduction is one of the largest tax breaks available to homeowners, but it only pays off if you actually itemize — and in recent years, fewer and fewer households have. After the standard deduction was roughly doubled, a couple filing jointly who claims it automatically subtracts $29,200 from taxable income without ever keeping a receipt. Unless your itemized deductions — mortgage interest, state and local taxes (SALT), charitable gifts, and certain medical costs — add up to more than that, the mortgage interest deduction may save you nothing at all.
This calculator does the real comparison. It estimates the interest you will pay in your first year on an amortizing home loan, adds your other itemized deductions, stacks that total against your filing-status standard deduction, and then multiplies the difference by your marginal tax bracket to show your actual federal tax savings. Plug in your numbers and the answer is immediate: itemize, or take the standard deduction.
How to Use
- Enter the Mortgage Loan Amount — the principal you are borrowing (or the remaining balance if you already own the home).
- Set your Mortgage Interest Rate — your current note rate. If you have not locked a rate yet, test a range around the national average.
- Choose your Loan Term. Because interest front-loads, a 30-year loan produces a much bigger early-year interest deduction than a 15-year loan at the same balance.
- Pick your Filing Status. It drives the standard deduction: Married Filing Jointly is $29,200, Single is $14,600, and Head of Household is $21,900.
- Add your State and Local Taxes (SALT). The TCJA caps the SALT deduction at $10,000 per year; the calculator applies that cap automatically, so enter what you actually paid and it will not let the number exceed $10,000.
- Add Charitable Gifts and Other Itemized — cash donations to qualified 501(c)(3)s and other qualifying itemized expenses. Large unreimbursed medical expenses (above 7.5% of your AGI) are not modeled here; see the FAQ.
- Enter your Marginal Tax Bracket — your top federal rate, such as 22% or 24%. The higher your bracket, each dollar of extra deduction is worth more.
The result card shows your estimated Year-1 mortgage interest, the standard deduction for your status, your combined itemized total, whether you should itemize or take the standard deduction, the extra deduction itemizing actually unlocks, and your estimated federal tax savings.
How the Deduction Actually Works
The IRS lets you deduct the mortgage interest you actually pay during the year, up to a cap on eligible principal. For mortgages taken out after December 15, 2017, you can deduct interest on up to $750,000 of principal ($375,000 if married filing separately); for older loans grandfathered in, the cap is $1 million. Interest on home-equity debt is deductible only when the proceeds are used to buy, build, or substantially improve the home securing the loan.
Because a standard amortizing loan charges interest on the remaining balance, your deduction is largest in year one and shrinks every year as you pay down principal. On a $400,000 loan at 7.0% for 30 years, the monthly payment is about $2,661, and the interest portion over the first twelve months is roughly $27,900 — before the balance slowly declines.
The decisive question is not "how much interest did I pay?" but "is that interest enough, together with my other deductions, to beat the standard deduction?" If your itemized total lands below the standard amount, the mortgage interest deduction contributes $0 to your tax bill.
Examples
Example 1 — Itemizing barely wins. A married couple has a $400,000 loan at 7.0% for 30 years. Year-1 interest is about $27,871. They also pay the maximum $10,000 SALT. Their itemized total is $37,871, which beats the $29,200 standard deduction by $8,671. In a 22% bracket, that extra deduction saves them about $1,908 on their federal tax bill.
Example 2 — The standard deduction wins. The same couple, but without any SALT or charitable gifts, itemize only $27,871 of mortgage interest. That is below the $29,200 standard deduction, so they take the standard amount — and the mortgage interest deduction itself delivers $0 of tax savings. This is the most common outcome after the 2017 tax law.
Example 3 — A high-balance loan subject to the $750k cap. On a $1,000,000 mortgage at 7.0% for 30 years, the full-loan Year-1 interest would be about $69,678, but because the loan was taken out after December 15, 2017, only the interest attributable to the first $750,000 of principal is deductible — roughly $52,257. Adding the capped $10,000 SALT brings itemized deductions to about $62,257, which beats the $29,200 standard deduction by about $33,057. At a 22% marginal rate, itemizing saves roughly $7,273 — a meaningful number, but far less than the $11,105 you would see if the entire million-dollar balance were deductible. Loans grandfathered in before the TCJA keep the old $1 million cap.
FAQ
How much mortgage interest can I deduct?
You can deduct the mortgage interest you actually pay in the year on eligible home-acquisition debt, up to the principal cap ($750,000 for post-2017 loans, $1 million for grandfathered loans). The deduction is the interest portion of your payments, not your total mortgage payment — principal repayment is not deductible.
Should I itemize or take the standard deduction?
Compare your total itemized deductions (mortgage interest plus SALT, capped at $10,000, plus charitable and qualifying medical costs) against your filing-status standard deduction. If itemized deductions are higher, itemize; otherwise take the standard deduction. For most households after 2018, the standard deduction is the better choice.
At what income level does the mortgage interest deduction help?
The deduction helps most in higher marginal tax brackets and early in the loan, when interest is highest. A homeowner in the 22% or 24% bracket with a large mortgage and $10,000+ SALT benefits the most; a household in the 12% bracket with modest itemized costs usually gains little or nothing over the standard deduction.
Is the mortgage interest deduction worth it?
It depends on whether your itemized deductions exceed the standard deduction. If they do, each extra dollar of interest reduces your tax by your marginal rate. If they do not, paying extra mortgage interest to generate a deduction is poor value — you are spending $1 to save less than $1.
Can I deduct interest on a second home or HELOC?
Interest on a second home you do not rent out is generally deductible under the same cap. A home-equity loan or HELOC is deductible only if the funds are used to buy, build, or substantially improve the home securing the debt; using the cash for other expenses makes that interest nondeductible.
Does refinancing affect my mortgage interest deduction?
Generally, yes, you can still deduct the interest on a refinanced loan, but the eligible principal cap carries over from the original loan unless you cash out to improve the home. The deduction is also front-loaded: the earlier you are in the new loan, the larger the interest portion.
Disclaimer
This mortgage interest deduction calculator is provided for informational purposes only and does not constitute tax, legal, or financial advice. Estimates use a standard amortization model and 2024 standard deduction amounts; actual 2025 figures, phase-outs, eligibility rules, and state taxes differ by your situation. Interest caps, SALT limits, and grandfathered-loan rules are simplified. Consult a qualified tax professional before filing or making decisions based on these results.