"You get the mortgage interest deduction" is one of the most persistent arguments for buying a home, and for most American households it has been worth nothing since 2018. Understanding why takes five minutes and can change the buy-versus-rent arithmetic materially.
#How the deduction actually works
Mortgage interest is an itemised deduction. You only benefit from itemised deductions if their total exceeds the standard deduction you would otherwise take automatically.
The 2017 tax law roughly doubled the standard deduction while capping the state and local tax deduction at $10,000. The combined effect was that the proportion of filers who itemise fell from roughly 30% to around 10%.
If you take the standard deduction, your mortgage interest produces zero tax benefit. Not a reduced benefit — zero.
#The arithmetic
Add your potential itemised deductions:
- Mortgage interest paid during the year
- State and local taxes, capped at $10,000 combined for income and property tax
- Charitable contributions
- Medical expenses above 7.5% of adjusted gross income
Compare the total against the standard deduction for your filing status.
Take a married couple with a $360,000 mortgage at 6.4%. First-year interest is roughly $22,900. Add $10,000 of capped SALT and $2,000 of charitable giving for $34,900 of itemised deductions.
Against a standard deduction near $30,000, they itemise — but the benefit is only the excess: $4,900. At a 22% marginal rate, that is worth about $1,078 a year, not the $5,038 that 22% of $22,900 would suggest.
That distinction is where nearly everyone goes wrong. The benefit is the marginal rate applied to the amount by which itemising exceeds the standard deduction, never the full interest figure.
#Why the benefit shrinks every year
Mortgage interest falls as the loan amortises. By year ten of a 30-year loan, annual interest on that same $360,000 mortgage has dropped by roughly a quarter. Once total itemised deductions fall below the standard deduction, the benefit disappears entirely and does not come back.
For most borrowers the deduction is worth something in the early years and nothing thereafter — the opposite of the impression the argument creates.
#Who does still benefit meaningfully
High-value mortgages in high-tax states. A $900,000 mortgage generates enough interest to clear the standard deduction comfortably for many years.
High earners with large charitable giving. Charitable contributions push the itemised total above the threshold, so mortgage interest adds on top rather than competing.
High marginal rates. The value is the excess multiplied by your marginal rate, so a filer in the 35% bracket gets meaningfully more than one at 12%.
Note that these describe a comparatively small and affluent slice of homeowners — which is the standing critique of the deduction as housing policy.
#What to do about it
Check your last tax return. Look at whether you itemised. If you took the standard deduction, set the tax benefit input in the rent vs buy calculator to zero and re-run. Buying will look meaningfully less attractive, and that is the accurate picture.
If you do itemise, calculate the excess, not the total. Subtract the standard deduction from your itemised total, multiply by your marginal rate, and divide by twelve for a monthly figure.
Consider bunching. If you are near the threshold, concentrating two years of charitable giving into one — via a donor-advised fund, for instance — lets you itemise in one year and take the standard deduction in the next, capturing more total benefit.
#The wider point
The mortgage interest deduction is the most cited and least understood argument for buying. Even where it applies it is a partial rebate on a cost, not a benefit — you are still paying the interest, and getting some fraction of it back.
Buy a house because you want to live in it, because the price-to-rent ratio is sensible, and because you will stay long enough to clear transaction costs. Treat any tax benefit as a rounding adjustment rather than a reason.
Frequently asked questions
Is mortgage interest still deductible?
Yes, on up to $750,000 of acquisition debt for loans taken after December 2017, and $1,000,000 for older loans. But it only helps if your total itemised deductions exceed the standard deduction, which is now uncommon.
Are property taxes deductible too?
They fall under the state and local tax deduction, which is capped at $10,000 combined with state income tax. In high-tax states that cap is frequently reached by income tax alone, leaving property tax with no deductible value.
Does the deduction apply to a second home?
Interest on a second home can qualify, but the $750,000 acquisition debt limit applies across both properties combined, not per property.