Mortgage Interest Tax Deduction Calculator

How the Mortgage Interest Deduction Works

The mortgage interest deduction lets you subtract the interest you pay from your taxable income—but only if you itemize deductions instead of taking the standard deduction. Since the Tax Cuts and Jobs Act of 2017, the standard deduction nearly doubled, making itemizing less attractive for many homeowners.

In 2023, the standard deduction is $27,700 for married couples filing jointly and $13,850 for singles. You only benefit from itemizing if your mortgage interest, property taxes (capped at $10,000), charitable donations, and medical expenses combined exceed those thresholds.

On a $400,000 loan at 6%, your first-year interest is about $24,000. Add $6,000 in property taxes and you're at $30,000—above the standard deduction by $2,300. If you're in the 24% tax bracket, that saves you about $552. The benefit shrinks each year as you pay less interest and more principal.

Who Benefits Most from the Mortgage Deduction

High earners with large mortgages in high-tax states benefit most. If you're in the 35% bracket with a $700,000 mortgage at 6%, you're paying $42,000 in interest the first year. Combined with the $10,000 SALT cap, you're at $52,000 in itemized deductions. That beats the standard deduction by $24,300, saving you about $8,505 in taxes.

Low-to-moderate earners with small mortgages rarely benefit anymore. A $200,000 loan at 6% generates $12,000 in interest. Even with $5,000 in property taxes, you're at $17,000—well below the standard deduction. You'd be better off taking the standard deduction and ignoring itemizing.

The sweet spot is roughly $350,000+ in mortgage debt combined with significant state taxes or charitable giving. Below that, the standard deduction usually wins. Run the numbers each year because the benefit declines as your balance and interest payments shrink.

Effective Rate and Real Cost Considerations

Your effective mortgage rate is what you actually pay after tax savings. If you're in the 24% bracket and can deduct all your interest, a 6% mortgage costs you about 4.6% after taxes (6% × 0.76). That makes the mortgage cheaper than it appears.

But don't let the tax tail wag the financial dog. Some people justify bigger mortgages because 'the interest is deductible.' That logic only makes sense if you were going to borrow that much anyway. Paying $1,000 in interest to save $240 in taxes still costs you $760. You're not coming out ahead—you're just losing less.

Also remember the deduction phases out over time. As you pay down principal, your interest drops, and eventually you fall below the standard deduction threshold. Plan for that. The mortgage deduction might save you $3,000 in year one, but only $500 in year fifteen. Don't base long-term decisions on a temporary tax break.