The Mortgage Interest Deduction: How Much Do You Really Save?
"You'll get it back at tax time." It's the most repeated line in home buying, and it is the most misunderstood. The mortgage interest deduction is real, but for most people in 2026 it saves far less than they expect — and for many it saves nothing at all. This post explains exactly how the deduction works, why the standard deduction quietly cancels it for most homeowners, and then lets you run your own numbers with a built-in calculator using 2026 federal brackets and your state.
What the deduction actually is
Mortgage interest is an itemized deduction. When you file, you choose the larger of two things: the flat standard deduction, or the sum of your itemized deductions (mortgage interest, state and local taxes, charitable gifts, and a few others). You don't get both. Crucially, a deduction is not a credit — it lowers the income you're taxed on, not your tax bill dollar-for-dollar. A $10,000 deduction in the 22% bracket is worth about $2,200, not $10,000.
The standard-deduction hurdle
This is the part nobody mentions at closing. For 2026 the standard deduction is roughly $16,100 for single filers and $32,200 for married couples filing jointly. Your mortgage interest only helps to the extent your total itemized deductions climb above that number. If a married couple has $20,000 of mortgage interest and little else, they're still better off taking the $32,200 standard deduction — and their mortgage interest delivers zero federal benefit. Since the standard deduction nearly doubled in 2018, the large majority of homeowners are in exactly this position.
The deduction starts mattering when mortgage interest plus your state and local taxes (capped, but much higher in 2026 than the old $10,000 limit) clear the standard deduction. Only the amount above the hurdle is actually working for you, and only at your marginal tax rate.
Two more rules that shape the number
- The $750,000 federal cap — but your state may differ. For federal taxes, loans taken after December 15, 2017 can only deduct interest on the first $750,000 of mortgage debt. Some states are more generous and decouple from this limit: California, for example, allows interest on up to $1,000,000 of acquisition debt (plus another $100,000 of home-equity debt), regardless of when the loan originated. The calculator below applies the federal cap to your federal savings and your state's own cap to the state savings.
- It shrinks every year. A mortgage is front-loaded with interest, so your deduction is largest in year one and falls steadily as you pay down principal. The benefit you feel early fades — and often drops below the standard-deduction hurdle entirely in later years.
Run your numbers (2026)
Enter your details below. The calculator amortizes your loan, applies the 2026 federal brackets and standard deduction, the $750,000 cap, and your state's actual 2026 tax brackets and standard deduction (every graduated state is entered bracket-by-bracket from the Tax Foundation's 2026 tables; flat-tax states use their exact rate), then shows the mortgage interest you pay each year and how much tax the deduction actually saves you — federal and state. It also asks for your property tax and any other itemized deductions, because those stack with mortgage interest to clear the standard-deduction hurdle — leave them out and the deduction looks far smaller than it really is.
Estimates only, not tax advice. Federal savings use the $750,000 acquisition-debt cap; state savings use that state's own cap where it differs (California and New York use $1,000,000). State income tax is computed from each state's actual 2026 brackets and standard deduction (source: Tax Foundation, 2026). States that don't allow a separate mortgage-interest deduction show $0 state savings; a couple (Utah, Wisconsin) grant it through a tax credit, so those are approximate. State itemization phase-outs, personal exemptions, property-tax interplay, and conformity quirks aren't modeled — confirm with a tax professional.
The deduction is only one piece of the cost of a loan. Model the whole picture — payment, total interest, points, and extra payments — and compare scenarios side by side.
The bottom line
The mortgage interest deduction is best treated as a possible discount, not a guarantee. If your interest plus state taxes don't clear the standard deduction, it's worth nothing — and even when it helps, it returns only your marginal rate on the amount above the hurdle, shrinking every year as you pay down the loan. Never buy more house, or a bigger loan, "for the tax write-off." Run the real numbers first, and confirm them with a tax professional before you count on a dollar of it.