Mortgage Interest Deduction Calculator: How Much of Your Interest Is Deductible
Enter your average mortgage balance and the interest you paid, and see your qualified loan limit, the deductible share line by line, and whether itemizing beats the standard deduction.
Home mortgage interest is deductible on up to $750,000 of debt used to buy, build or substantially improve your home if the loan dates from after December 15, 2017, or $1,000,000 for debt incurred from October 14, 1987, through December 15, 2017 (half each if married filing separately). Over the limit, only a share counts: on $900,000 borrowed after 2017 with $54,000 of interest, the share is 0.833, so $44,982 is deductible and $9,018 is not.
This page works the Publication 936 (2025) worksheet for general education. It is not tax advice and not a tax return. It assumes every balance you enter is grandfathered debt or home acquisition debt on a qualified home and leaves out mixed-use mortgages, points, home equity money spent on other things and state taxes. The tax-saving figure uses 2026 federal brackets for single and joint filers only, with no credits or other adjustments. Check the current publication or a qualified tax professional before you file.
Deductible mortgage interest
$44,982.00
Your qualified loan limit is $750,000.00 against $900,000.00 of debt, so 0.833 of the interest is deductible and $9,018.00 is not.
| Line 1: Grandfathered debt (before Oct 14, 1987) | $0.00 |
| Line 2: Debt from Oct 14, 1987, to Dec 15, 2017 | $0.00 |
| Line 3: Limit for that debt | $1,000,000.00 |
| Line 4: Larger of line 1 and line 3 | $1,000,000.00 |
| Line 5: Line 1 + line 2 | $0.00 |
| Line 6: Smaller of line 4 and line 5 | $0.00 |
| Line 7: Debt after Dec 15, 2017 | $900,000.00 |
| Line 8: Limit for that debt | $750,000.00 |
| Line 9: Larger of line 6 and line 8 | $750,000.00 |
| Line 10: Line 6 + line 7 | $900,000.00 |
| Line 11: Qualified loan limit | $750,000.00 |
| Line 12: Total average balance | $900,000.00 |
| Line 13: Interest paid | $54,000.00 |
| Line 14: Line 11 / line 12 | 0.833 |
| Line 15: Deductible mortgage interest | $44,982.00 |
| Line 16: Interest that is not deductible | $9,018.00 |
Estimated 2026 federal tax saving: $12,381.68
Itemized deductions of $56,982.00 beat the $16,100.00 standard deduction.
Embed this calculator on your site →
About the Mortgage Interest Deduction Calculator
The deduction is capped by the size of the debt, not the size of the interest. Publication 936 sets the cap through a 16-line worksheet: debt from before October 14, 1987, is grandfathered; debt taken out from then until December 15, 2017, falls under a $1,000,000 limit; and debt taken out after December 15, 2017, falls under $750,000, with each limit halved for married filing separately. The worksheet blends the three into one qualified loan limit on line 11. If your total average balance on line 12 is no higher, every dollar of interest is deductible. If it is higher, line 14 divides the limit by the balance, rounded to three places, and only that share of the interest counts. Use average balances. The first and last balance method, the start-of-year balance plus the end-of-year balance divided by two, applies only if you borrowed nothing new on the loan that year, prepaid no more than one month's principal and made level payments at fixed intervals at least twice a year. It only helps if you itemize, so the optional estimate compares your itemized total with the 2026 standard deduction of $16,100 single or $32,200 joint and shows the federal tax difference.
Frequently asked questions
How does a refinance count?+
A loan that refinances home acquisition debt is still home acquisition debt, but only up to the principal balance of the old mortgage just before the refinance. Cash taken out on top that is not used to buy, build or substantially improve the home is not acquisition debt, so leave that part out of the balances here.
Is home equity loan interest deductible?+
Only when the loan money was used to buy, build or substantially improve the home that secures it. Interest on a home equity loan spent on a car, tuition or credit card debt is not home mortgage interest, whenever the loan was taken out, and this page does not include it.
Why does the interest save me nothing in tax?+
Because the deduction counts only if your itemized deductions add up to more than the standard deduction. With $15,000 of interest and $10,000 of other deductions, a married couple has $25,000 itemized against a $32,200 standard deduction, so taking the standard deduction is better and the interest makes no difference to the tax.
Where do I find my balance and interest?+
Form 1098, the mortgage interest statement your lender sends each year, shows the interest you paid. Your lender's monthly statements or loan portal show the balances, and the helper on this page averages the start and end of year balances, which is valid only under the conditions in the explanation below.
Embed this calculator
Free to use on your own site. Paste this snippet where you want the mortgage interest deduction calculator to appear — it resizes itself automatically.
<iframe
src="https://manytools.co/embed/mortgage-interest-deduction-calculator"
title="Mortgage Interest Deduction Calculator by ManyTools"
data-manytools="mortgage-interest-deduction-calculator"
width="100%"
height="640"
loading="lazy"
style="border:0;width:100%;max-width:720px"></iframe>
<script>
(function () {
window.addEventListener("message", function (e) {
if (e.origin !== "https://manytools.co") return;
var d = e.data || {};
if (d.type !== "manytools:embed:height" || d.slug !== "mortgage-interest-deduction-calculator") return;
var f = document.querySelector('iframe[data-manytools="mortgage-interest-deduction-calculator"]');
if (f && d.height) f.style.height = d.height + "px";
});
})();
</script><a href="https://manytools.co/finance/mortgage-interest-deduction-calculator">Mortgage Interest Deduction Calculator by ManyTools</a>