A 6% mortgage sounds like a 6% mortgage. But if you itemize your deductions, your real, after-tax cost of that debt can be meaningfully lower — which matters a lot if you're trying to decide whether extra money should go toward your mortgage or into the market. Here's the part most articles skip: the deduction is smaller than the naive math suggests, and for 2026 specifically, a recent tax law change makes it worth revisiting even if you ruled out itemizing a few years ago.
The Naive Math (and Why It's Wrong)
The common shortcut looks like this: take your mortgage rate, multiply by (1 − your tax bracket), and call that your "real" rate. A 6% rate at a 24% federal bracket becomes 4.56%. Looks simple. It's also usually too generous.
The deduction only helps if two things are both true:
- You itemize instead of taking the standard deduction — otherwise the mortgage interest deduction does nothing for you at all.
- Your itemized total exceeds what the standard deduction already gives you for free — so the real benefit is only on the amount above that baseline, not on every dollar of interest you paid.
Example: $500,000 mortgage at 6% ($30,000/yr interest), 24% federal bracket, married filing jointly, $10,000 in other itemizable deductions (property tax, etc.).
The 2026 Standard Deduction — Your Baseline
For the 2026 tax year, the standard deduction is $16,100 for single filers, $32,200 for married couples filing jointly, and $24,150 for head of household. If your total itemized deductions — mortgage interest, state and local taxes, charitable gifts, and a few others — don't clear that bar, itemizing gives you nothing extra, and the mortgage interest deduction is effectively worth $0 to you.
The Real 2026 Change: The SALT Cap Went Up — A Lot
This is the part worth paying attention to if you're in a higher-tax state. The cap on deducting state and local taxes (property tax plus state income tax, known as "SALT") was capped at just $10,000 for years — a limit that pushed a huge number of homeowners toward the standard deduction, since their property taxes alone often used up that entire cap with nothing left over for mortgage interest to add to.
For 2026, that cap rose to $40,400. That's a real, structural change — not a minor inflation adjustment. For homeowners paying meaningful property tax, it means itemizing (and therefore actually benefiting from the mortgage interest deduction) is back on the table in a way it hasn't been in years.
A Worked Example
Sarah and Mike own a home in Bergen County, NJ. Married filing jointly, combined income puts them in the 24% federal bracket.
| Item | Amount |
|---|---|
| Mortgage interest paid this year | $18,000 |
| Property tax + state income tax (SALT) | $19,500 |
| Total itemized deductions | $37,500 |
| 2026 standard deduction (MFJ) | $32,200 |
| Amount itemizing beats the standard deduction by | $5,300 |
Because their SALT deduction alone ($19,500) is now comfortably under the new $40,400 cap, all of it counts. Itemizing beats their standard deduction by $5,300 — meaning $5,300 of their $18,000 in mortgage interest is doing real tax work, taxed away at their 24% bracket. That's a benefit of about $1,272, not the $4,320 a naive "24% of all $18,000 in interest" calculation would suggest.
What This Means for the Payoff-vs-Invest Decision
Once you know your real, itemizing-adjusted tax savings, you can back into your true effective rate and use that — not your nominal rate — when comparing debt payoff against investing.
Their nominal rate is 6%. Their true effective rate, after correctly accounting for the standard deduction baseline, comes out closer to 5.6% — a real but modest reduction, nowhere near the naive 4.56% estimate. That's still meaningful: it's the number to actually plug into a pay-off-vs-invest comparison, not the sticker rate on the loan.
Run Your Real Numbers → CalcFactorThe Takeaway
- The mortgage interest deduction is worth less than the "rate × tax bracket" shortcut suggests for most homeowners.
- It's only worth anything at all if your itemized total clears the standard deduction — $16,100 single / $32,200 married filing jointly / $24,150 head of household for 2026.
- The 2026 SALT cap increase to $40,400 is a real, structural change that may bring itemizing back into play for homeowners in higher-tax counties who ruled it out in recent years.
- Once you know your true effective rate, use that number — not your nominal rate — when deciding between paying down your mortgage and investing extra cash.