Mortgage Interest Deduction: How It Can Lower the True Cost of Buying a Home
- Loan Genie Insights
- Mar 4
- 4 min read
Updated: Mar 18
The Bottom Line
The Mortgage Interest Deduction can significantly reduce the real cost of homeownership, especially for buyers purchasing mid-to-higher priced homes.
Recent tax changes under the One Big Beautiful Bill Act (OBBBA), signed by President Donald Trump, increased the cap on state and local tax (SALT) deductions to $40,000 for households earning under $500,000. Because SALT deductions combine with mortgage interest when itemizing deductions, this change makes it easier for homeowners to benefit from the mortgage interest deduction again.
For buyers in the 22% federal tax bracket, the tax savings can look roughly like this:
Home Price | Mortgage (20% down) | First-Year Interest | Estimated Annual Tax Savings |
$400,000 | $320,000 | ~$20,800 | Minimal |
$600,000 | $480,000 | ~$31,000 | ~$3,000–$6,800 |
$750,000 | $600,000 | ~$38,700 | ~$6,000–$8,500 |
For many buyers, this translates to roughly $300–$700 per month in reduced effective housing cost once tax savings are factored in. However, this benefit is often overlooked by both mortgage calculators and home buyers, leading many people to underestimate the financial advantage of owning a home.
How the Mortgage Interest Deduction Works
When you buy a home with a mortgage, a large portion of the early payments goes toward interest, not principal. The IRS allows homeowners to deduct this interest from their taxable income if they itemize deductions.
For example:
Mortgage interest paid in a year:
$35,000
Tax bracket:
22%
Tax savings:
$35,000 × 22% = $7,700
This effectively reduces the cost of the mortgage because part of the interest expense is offset by lower taxes.
What This Means for the Effective Mortgage Rate
Another way to understand the benefit is to think of it as a discount on the mortgage interest rate.
Because the tax deduction reduces the cost of interest, the after-tax interest rate is lower than the quoted mortgage rate.
A simple approximation is:
Effective after-tax rate = Mortgage rate × (1 − tax rate)
For a buyer in the 22% tax bracket with a 6.5% mortgage rate:
6.5% × (1 − 0.22) ≈ 5.07% effective rate
In other words, the tax deduction makes a 6.5% mortgage behave more like a ~5.1% mortgage in terms of after-tax cost.
This is one reason why the mortgage interest deduction can materially change the economics of buying a home.
Two Important Limits to Understand
Two caps affect how much homeowners can deduct.
Mortgage Interest Deduction Limit
Homeowners can deduct interest only on the first $750,000 of mortgage debt.
For most home buyers purchasing homes under roughly $900,000 with a typical down payment, the entire mortgage still falls within this limit.
State and Local Tax Deduction Cap
The One Big Beautiful Bill Act signed by President Trump increased the deduction limit for state and local taxes to $40,000 for households earning under $500,000. Before the tax change, the SALT deduction was capped at $10,000, which made it much harder for homeowners to exceed the standard deduction and benefit from mortgage interest deductions.
SALT deductions include:
state income tax
property taxes
These deductions combine with mortgage interest when calculating total itemized deductions.
When the Mortgage Interest Deduction Starts to Matter
The key factor is whether a homeowner's itemized deductions exceed the standard deduction. For many households, the mortgage interest deduction starts having a noticeable financial impact once home prices reach approximately $600,000.
Example scenario:
Home price: $600,000 Mortgage: $480,000 Interest rate: 6.5%
First-year mortgage interest:
≈ $31,200
Typical SALT deductions:
Category | Amount |
State income tax | $18,000 |
Property tax | $8,000 |
Total SALT | $26,000 |
Total:
$57,200
Assuming a standard deduction of roughly $29,000 for a married couple, the additional deductible amount is:
$57,200 − $29,000 = $28,200
Tax savings in the 22% bracket:
$28,200 × 22% = $6,204
Monthly impact:
≈ $517 per month
Why Many Mortgage Calculators Ignore This
Most mortgage calculators focus on estimating the monthly mortgage payment,
but they rarely account for tax deductions because calculating the true tax benefit requires information about:
income level
filing status
state taxes
charitable deductions
current tax law
Because of these variables, calculators usually show only the gross payment, not the after-tax cost of borrowing.
Why Home Buyers Often Overlook the Deduction
Many home buyers also ignore the mortgage interest deduction when evaluating affordability.
There are several reasons:
Tax complexity: Many buyers are unsure whether they will itemize deductions.
Confusion about tax law changes: The previous SALT cap significantly reduced the deduction's usefulness, so many buyers assume it still has little value.
Mortgage calculators rarely include it:Since most calculators do not show after-tax savings, buyers focus only on the headline monthly payment.
As a result, buyers may underestimate the financial benefits of owning a home, particularly when purchasing mid-priced or higher-priced homes.
Final Takeaway
The mortgage interest deduction remains one of the largest tax benefits of homeownership.
Because the One Big Beautiful Bill Act signed by President Trump raised the SALT deduction cap to $40,000, more homeowners are now able to itemize deductions and benefit from mortgage interest deductions.
For many buyers:
the deduction begins to matter around $600,000 home purchases
tax savings can reach $300–$700 per month
the benefit grows with larger mortgages until reaching the $750,000 mortgage limit
When viewed through the lens of interest costs, the deduction effectively reduces a 6.5% mortgage rate to roughly a 5.1% after-tax rate for buyers in the 22% tax bracket.
Understanding this tax benefit helps buyers evaluate the true after-tax cost of owning a home, rather than relying only on the headline mortgage payment.
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