Mortgage Interest Tracing

By Jason Watson, CPA
Posted Thursday, July 16, 2026

Generally, interest expense can fall into any of the following categories-

• Investment interest is interest on debt incurred to purchase property held for investment, such as stocks and mutual funds. The yearly deduction is generally limited to net investment income. If the investment generates tax-exempt income, the interest is not deductible.
• Residence interest is interest on a home mortgage and is generally deductible as an itemized deduction on Schedule A, subject to loan limitations. Qualified residence is the IRS terminology, and it generally includes your main home and one second home.
• Passive activity interest is interest on debt incurred for business or income-producing activities in which you don’t materially participate. This is usually deductible only if income from passive activities exceeds expenses from those activities. Your rental property might fall under this category depending on your participation.
• Trade or business interest is interest on debt incurred for activities in which you do materially participate and can generally be deducted in full. Your rental property might also fall under this category.
• Personal interest, such as personal credit card debt or personal automobile interest, is not deductible.

Can you borrow against the equity in your primary residence to purchase a rental property? Absolutely, and it is a common strategy. Can you sidestep the qualified residence interest limitations and deduct the mortgage interest on Schedule E? Generally, yes. This is called interest tracing, and the concept is quite simple: the use of the loan proceeds generally determines the category of interest expense, regardless of which property secures the loan.

If you borrow against your home and use the money to buy or improve a rental property, the interest is generally traced to the rental activity and deducted on Schedule E. Yes, there might be capitalized interest under IRC Section 266 for an improvement, but you get the idea.

However, tracing cuts both ways. If you borrow against a rental property and use the money personally, that interest does not become rental interest simply because the rental property secured the loan.

As you likely know, Schedule A has its own rules for qualified residence interest, including the requirement that the debt be secured by the qualified residence. That matters when the fact pattern runs in reverse. Yeah, can’t have it both ways.

Treasury Regulations 1.163-8T(c) reads in part-

The last sentence is the important one: “debt proceeds and related interest expense are allocated solely by reference to the use of such proceeds.” In other words, follow the money.

As you might be aware, the Tax Cuts and Jobs Act of 2017 limited qualified residence interest for many taxpayers. For loans after December 15, 2017, the acquisition debt limit is generally $750,000. This means if you have $50,000 in mortgage interest on a $1,000,000 qualified residence loan, only 75%, or $37,500, would be eligible for deduction on Schedule A of your Form 1040 tax return.

How does this play into the interest tracing rules? Treasury Regulations 1.163-8T(m) reads-

What does this gibberish mean? Loan interest is chopped up, or allocated if you want the fancy accounting term, depending on the ultimate use of the loan proceeds without regard to limitations. However, once the interest is allocated to various categories, then the limitations for that category come into play. Qualified residence interest has its limits. Passive activity interest has its limits. Business interest might have its limits. Personal interest is just sad and generally nondeductible.

Now what? Here are some examples.

Let’s say you own a primary residence with $500,000 in mortgage loan debt. You borrow another $600,000 for home improvements and to buy a rental property. Of the $600,000, $200,000 is used for home improvements, with the remaining $400,000 used for the rental property purchase. Freshen up that kitchen and master bath plus build some wealth. Nice! Or is it primary bath? Do you use a primary lock to lock it, or a Master Lock? We digress…

The interest on the $200,000 portion is deductible on Schedule A, assuming the home improvement debt otherwise qualifies, alongside the first loan interest since both balances combined are $750,000 or less. The interest on the $400,000 portion is deductible on Schedule E of the new rental property, subject to the usual rental, passive activity, at-risk and business interest limitations.

We’ll reverse it a bit. Let’s say you borrow $1,000,000 against your rental property to buy a primary residence and to also buy another rental property. Why not, right? $800,000 is used to buy the primary residence and $200,000 is used to acquire the second rental.

The $200,000 portion used to acquire the second rental property is deductible on Schedule E, subject to the usual rental, passive activity, at-risk and business interest limitations. Of course, you know this already! However, the $800,000 portion used to buy the primary residence is not deductible on Schedule A as qualified residence interest if the loan is secured only by the rental property. Tracing tells us the proceeds were used for a residence, but IRC Section 163(h)(3) and the qualified residence interest rules also require the debt to be secured by the qualified home. If the debt is later secured by the residence and otherwise meets the qualified residence interest rules, the analysis can change from that point forward.

Here are some pitfalls-

• There are ordering rules should you mix borrowed funds with un-borrowed funds. As such, keep monies separated to assist in the tracing part of the interest tracing provisions.
• The qualified home limitation of $750,000 referenced above encompasses your main and second home. Depending on your objectives and tax footprint, if your second home slips into being a rental property, the interest might need to be allocated between Schedule A and Schedule E under the vacation home rules. See our vacation home rules section on page 128.

Keep in mind that the cost of your equity is usually more expensive than the cost of borrowing. Not always, but usually. We could get into the tax-effected rate of return on your equity versus the property appreciation-effected cost of borrowing, internal rates of return and all the hoopla, but generally using other people’s money to fund your real estate investment empire is preferred. Entire books and endless internet rabbit holes are dedicated to real estate leverage.

Please see our capitalizing construction mortgage interest section which discusses the capitalization of mortgage interest during construction or renovations.