Background
The mortgage interest deduction was created to encourage homeownership. The Tax Cuts and Jobs Act (TCJA), effective for most loans after December 15, 2017, lowered the cap on deductible acquisition debt and changed the treatment of home‑equity loans. These adjustments reduced the number of taxpayers who benefit from the deduction because the standard deduction increased under TCJA (many taxpayers now take the standard deduction instead of itemizing). For IRS guidance, see Publication 936 (Home Mortgage Interest Deduction) and the Form 1098 instructions (IRS.gov).
How the rules work today
- Qualified interest: Interest on a mortgage you use to buy, build, or substantially improve your main home or a second home generally qualifies as “qualified residence interest” and is deductible if you itemize on Schedule A (Form 1040) (IRS Publication 936).
- Dollar limits: For acquisition debt taken out after December 15, 2017, interest is deductible on up to $750,000 of combined mortgage debt ($375,000 if married filing separately). For mortgages originated before that date, the previous limit of $1,000,000 ($500,000 MFS) generally still applies.
- Home‑equity loans and lines of credit: Interest on these loans is deductible only if the proceeds are used to buy, build, or substantially improve the home that secures the loan. Interest on home‑equity debt used for other purposes (for example, paying off credit cards or buying a car) is not deductible under the TCJA rules.
- Reporting: Lenders report mortgage interest of $600 or more on Form 1098; you use that information to complete Schedule A when itemizing.
Practical examples
- Example A — Typical buyer (post‑2017 mortgage): A homeowner who closed on a $600,000 acquisition loan in 2019 can deduct interest on the full loan balance (subject to itemizing), because the loan is under the $750,000 cap.
- Example B — High‑balance purchase: A couple who bought a $1.2 million home in 2020 faces the $750,000 cap; only interest allocable to the first $750,000 is deductible. Any interest on the excess principal is nondeductible.
- Example C — Home‑equity use: Homeowner takes a $50,000 HELOC in 2021 and uses the funds to add a new kitchen. Interest on that HELOC may be deductible because it was used to substantially improve the home.
Common pitfalls to avoid
- Not itemizing: If you claim the standard deduction, you cannot also claim mortgage interest on Schedule A.
- Ignoring acquisition date: The Dec. 15, 2017 cutoff controls which dollar limit applies. Refinances generally keep the original acquisition date limit if the refinance does not increase principal beyond the original loan balance (check Pub. 936 and talk to your tax advisor).
- Misusing home‑equity funds: Document how you spent HELOC or home‑equity loan proceeds; the business/personal use affects deductibility.
Tax‑planning tips (practical)
- Keep Form 1098 and lender statements each year; reconcile interest reported with your records.
- Before refinancing or taking a HELOC, run the numbers: higher mortgage balances can exceed the deduction cap and may not produce a tax benefit large enough to justify closing costs.
- Compare itemizing vs the standard deduction annually; shifts in life events (marriage, children, medical expenses) can change the best choice.
- If you plan a large home improvement, time the loan so interest qualifies as acquisition/improvement debt.
Quick reference table
| Loan type | Acquisition date | Deductible interest rule |
|---|---|---|
| Acquisition mortgages | After Dec 15, 2017 | Deductible on up to $750,000 combined debt (or $375k MFS) |
| Acquisition mortgages | Before Dec 15, 2017 | Deductible on up to $1,000,000 combined debt (or $500k MFS) |
| Home‑equity loans/HELOCs | Any (post‑TCJA use test applies) | Deductible only if funds used to buy, build, or substantially improve the home that secures the loan |
Where to read more
- IRS Publication 936 — Home Mortgage Interest Deduction: https://www.irs.gov/publications/p936
- Form 1098 and reporting rules — see the IRS Form 1098 page: https://www.irs.gov/forms-pubs/about-form-1098
- Consumer Financial Protection Bureau — mortgage basics: https://www.consumerfinance.gov/owning-a-home/
Internal resources
- For how mortgage amortization affects the portion of each payment that’s interest (and therefore deductible), see: “How Amortization Affects Mortgage Interest Deductions” (FinHelp): https://finhelp.io/glossary/how-amortization-affects-mortgage-interest-deductions/
- For related tax breaks on your home, including property tax and energy credits, see: “Home‑Related Tax Breaks: Mortgage Interest, Property Taxes, and Energy Credits” (FinHelp): https://finhelp.io/glossary/home-related-tax-breaks-mortgage-interest-property-taxes-and-energy-credits/
Professional perspective and disclaimer
In my practice advising homeowners and middle‑income filers, I’ve seen two common outcomes: borrowers with modest balances still gain meaningful tax savings when they itemize, while many higher‑income buyers find the deduction’s value limited by the cap and by taking the standard deduction. This guide is educational only and does not replace personalized tax or legal advice. For decisions about refinancing, HELOCs, or complex ownership structures, consult a CPA or tax attorney familiar with current law.
Authoritative sources: IRS Publication 936 and CFPB guidance (links above).
