Does the Mortgage Interest Deduction Still Matter? For Most Buyers, No

Year-one interest on the default home is about $21,700, under the $32,200 joint standard deduction, so its tax value is zero. Plus the 2026 SALT cap, priced.

Written by Jonathan Nyst Updated September 2026 5 min read Taxes Every figure re-runnable

For most buyers since the 2018 tax law: no — its value is exactly zero. A deduction only helps to the extent that itemizing beats the standard deduction, and the 2026 standard deduction is $16,100 for single filers and $32,200 for married filing jointly. On our default scenario — a $420,000 home, 20% down at 6.5% — year-one mortgage interest is about $21,700. For a joint filer, that does not clear the bar on its own, so the celebrated deduction changes their tax bill by nothing. Roughly nine in ten filers take the standard deduction (88.6% of returns in tax year 2022, per IRS Statistics of Income), and the house does not change that for most of them.

Why doesn’t the deduction help most buyers?

Because the standard deduction is the hurdle, not the reward. Every taxpayer gets it with no receipts; itemizing replaces it rather than adding to it. So the real value of mortgage interest is not the interest times your tax rate — it is only the amount by which your itemized total exceeds the standard deduction, times your rate. A couple with $21,700 of interest and little else to itemize gets a tax benefit of zero dollars, because they would have deducted $32,200 anyway.

This is the single most common error in rent-vs-buy math, and it usually appears as a lender’s calculator quietly applying your marginal rate to every dollar of interest. That flatters buying by thousands of dollars a year that never arrive.

Who still genuinely benefits from itemizing?

Three groups, mostly. Single filers with large loans — the $16,100 bar is half the joint one, so the same $21,700 of interest clears it with room to spare. Buyers in high-tax states whose property and state income taxes push toward the SALT cap, stacking on top of interest. And buyers of expensive homes generally — more borrowed money, more interest, until the $750,000 loan-principal cap cuts the growth off.

But clearing the bar is not winning the argument. Our model prices the itemized-versus-standard difference exactly — including the 2026 $40,400 SALT cap and the $750,000 mortgage-interest limit — and even a $1.1M home for a couple who genuinely itemizes still lost to renting by about $561,000 over 15 years in our test scenario. The deduction softened the loss; it did not reverse it.

Doesn’t the SALT cap change this?

It caps how far the stacking can go, and for 2026 it is a much higher cap than it was. SALT is the itemized deduction for state and local taxes — property tax plus state income (or sales) tax. The One Big Beautiful Bill Act lifted it from $10,000 to $40,000 for 2025, rising 1% a year: $40,400 in 2026 ($20,200 married filing separately), reaching $41,624 by 2029, then reverting to $10,000 in 2030 unless Congress acts again. The catch is the phase-down: above $505,000 of modified adjusted gross income the cap shrinks by 30 cents per dollar of income until it hits a $10,000 floor at roughly $606,000. High earners in high-tax states — the people the raise sounds designed for — are precisely the ones phased back to the old cap.

For most buyers the raise changes the rent-vs-buy math by exactly nothing, because the cap is not the binding constraint; the standard deduction is. Property tax on the default $420,000 home is about $4,620 a year, nowhere near either cap. Add it to the $21,700 of year-one interest and a married couple reaches $26,320 — still short of their $32,200 standard deduction, so their SALT deduction is worth zero under any cap. A single filer does clear the $16,100 bar: itemizing narrows renting’s ten-year win from about $67,000 to about $36,000 on the default scenario, roughly $22,400 of tax savings. Note what did the work, though: it is the mortgage interest, and the $4,620 of property tax fit comfortably under the old $10,000 cap too. Rerun that scenario with the old cap and the result is identical to the dollar.

Where does the higher SALT cap actually matter?

Expensive homes, where property tax alone breaks $10,000. Our expensive-city scenario — a $1.1M home, $12,100 a year of property tax, a married couple itemizing over a 15-year stay — is the textbook case: under the old cap, $2,100 of that property tax was non-deductible every year. Rerun the scenario both ways and the raised cap improves the buying side by about $21,000:

That $21,000 is real — and it is a rounding error against the $561,000 verdict. The expensive-city math is decided by price-to-rent ratios and opportunity cost, not by tax policy; the 2026 raise softened buying’s loss there without coming close to reversing it. The cap is also the reason “buy a big house for the tax breaks” aged so badly: two of the three ingredients (interest and SALT) are capped, and the third (the standard deduction) roughly doubled in 2018.

Does the deduction ever flip the rent-vs-buy answer?

Rarely on the margin, never on its own in our testing. It arrives only for itemizers, only above the bar, and its size shrinks every year as the loan amortizes and interest falls. What actually decides the answer — the mortgage rate, the price-to-rent ratio, and how long you stay — moves the result by tens or hundreds of thousands. The deduction’s realistic contribution for an itemizing buyer is a modest fraction of that, front-loaded in the early years.

If you are counting on the deduction to make buying work, the honest translation is: the numbers do not work, and you are hoping the tax code rescues them. It mostly stopped doing that in 2018.

How does the calculator handle it?

Exactly, not with a checkbox. The calculator computes your itemized total each year — interest under the $750,000 cap, SALT under the $40,400 cap — compares it against your filing status’s standard deduction, and credits buying only with the genuine difference. It also taxes the renter’s portfolio gains, so neither side gets free money. The full tax treatment is documented on the methodology page, and the glossary defines every term this guide leans on. For the bigger decision this feeds into, start from is it better to rent or buy or the year’s rate picture in rent vs buy in 2026.

Two simplifications, both of which flatter buying: the model counts property tax toward the SALT cap but not your state income tax, which shares the same cap and may already fill it — in which case your property tax adds nothing — and it does not model the high-income phase-down, so above $505,000 of income its itemizing scenarios are optimistic. Both errors run in the conservative direction for a site whose default verdict favors renting.

Run your own numbers: if the deduction matters for you, the model will find it — and if it does not, you will see the answer without it, which is the answer you actually get.

Jonathan Nyst

Jonathan Nyst built RentVsBuyMath as an independent project — for himself first. He spent fifteen years marketing financial products, in banking, fintech and payments at CMO level, which is exactly how he knows what a lead-generation calculator looks like from the inside. This is the calculator without the funnel: he is not a lender, broker or agent, the site takes no referral fees, and nobody is paid more if you decide to buy. The whole model is public — every formula documented on the methodology page, the engine MIT-licensed, covered by automated tests including scenarios computed by hand to check it.

Drafted with AI from the engine's output; reviewed and published by Jonathan Nyst. How this site is made · Corrections