How Does a 1031 Exchange Work With a Mortgage: Debt and Boot

Here’s how a 1031 exchange works when there’s a mortgage on the property you’re selling: the sale proceeds pay off your existing loan at closing, a Qualified Intermediary holds whatever remains, and you then buy a replacement property whose price and new mortgage each equal or exceed the price and mortgage of what you sold. If your new debt comes in lower, you can make up the difference with your own cash. Fall short on either the total value or the total debt without offsetting it, and the shortfall becomes taxable, even though no money ever hit your pocket.

Why the Mortgage Is Part of the Exchange

Section 1031 of the Internal Revenue Code lets you defer capital gains tax when you sell investment or business real property and reinvest into another like-kind property.¹ The IRS doesn’t just look at your equity when it evaluates the exchange. It counts the entire property value, mortgage included.

Sell a $1,000,000 property carrying a $600,000 mortgage, and your exchange value is the full $1,000,000. The loan gets paid off from the sale proceeds, but the IRS still treats that payoff as part of the transaction. That’s the concept everything else builds on. Your mortgage isn’t separate from the exchange; it’s inside the math.

Why does that matter? Because Section 1031(b) says gain is taxable to the extent you receive money or non-like-kind property, and debt relief counts as receiving money.¹ If your total liabilities drop through the exchange, the IRS treats that drop as cash in hand.

The Two Numbers That Have to Match

To defer your entire gain, two things need to hold:

The replacement property’s purchase price must equal or exceed the sale price of the property you gave up.
The new mortgage on the replacement must equal or exceed the mortgage on the property you sold, unless you cover the gap with additional cash out of pocket.

A working example. You sell a rental for $800,000 with a $500,000 mortgage on it. To fully defer, the replacement must cost at least $800,000, and the new financing on it must be at least $500,000. Borrow only $400,000 on the new place, and the $100,000 difference is treated as a benefit you received.

Mortgage Boot and What It Costs

That taxable benefit from reduced debt is called mortgage boot, or debt boot. Anytime your total liabilities decrease through the exchange, the reduction is treated as if you pocketed cash, even though nothing actually moved into your account.² The IRS view is straightforward: you owed $500,000 before and $400,000 after, so you’re $100,000 better off.

Boot gets taxed, but only up to your realized gain on the sale. The tax hits at several layers:

Federal capital gains tax at 0%, 15%, or 20% depending on your taxable income.³
Depreciation recapture at up to 25% on the portion of gain attributable to depreciation you previously claimed.³
The 3.8% Net Investment Income Tax if your modified adjusted gross income exceeds $200,000 filing single or $250,000 filing jointly.⁴

State income tax may sit on top of the federal bill.

Plugging the Debt Gap With Your Own Cash

You are not required to take on an equal or larger mortgage on the replacement property. You just need the total consideration going in to cover what came out. The Treasury Regulations let you net all liabilities assumed against all liabilities relieved.² Come out with net debt relief, and you can offset it by adding cash at closing.

Sell with a $500,000 mortgage, buy with only a $350,000 mortgage, and you have $150,000 in debt relief. Contribute $150,000 of your own money to the replacement purchase, and the boot disappears. No tax. The IRS is checking that you didn’t pocket an economic benefit. Whether the old debt was replaced with new debt or with cash doesn’t matter, as long as the total value going in is at least what came out.

This is useful when interest rates or lender terms make it unattractive to borrow as much on the replacement property. You trade leverage for cash and keep the deferral.

How the Two Closings Actually Work

The exchange runs through a Qualified Intermediary, an independent party who holds the sale proceeds so you never have direct access to the funds. That’s what prevents constructive receipt, which would blow up the exchange.

At the sale of the old property, the settlement agent uses the proceeds to pay off your existing mortgage, commissions, and closing costs. Whatever remains goes directly to the Qualified Intermediary. You should never touch or control this money.

At the replacement purchase, your new lender funds the mortgage directly to the title company or escrow agent handling the closing. The Qualified Intermediary wires the held exchange funds to the same closing agent to cover the rest of the price. If you’re adding personal cash to offset reduced debt, that money moves to closing separately. You sign the new mortgage instrument and the closing disclosure. The Qualified Intermediary provides a final accounting statement showing every dollar that moved. Keep it, because you’ll need it at tax time.

Refinancing Before or After the Exchange

Investors sometimes want to refinance either the old property or the new one to pull cash out around an exchange. The IRS watches this closely. Under the step transaction doctrine, the agency can treat a refinance and an exchange as a single transaction when the two are closely linked in time and purpose. If it determines the refinance was a way to extract cash from the exchange tax-free, those refinance proceeds become taxable boot.

The risk is highest when you refinance the property you’re about to sell shortly before the exchange. Taking a larger loan, pocketing the extra cash, and then selling through a 1031 invites the argument that the whole sequence was designed to get cash out without tax. The defense is a legitimate business purpose independent of the exchange, such as a rate reduction you’d been working on for months.

Refinancing the replacement property after the exchange closes is generally treated as less risky, because you’ve already completed the exchange and taken title. A later refinance looks like a separate investment decision. Even so, waiting several months strengthens the argument that the two transactions were unrelated. Refinancing the week after closing invites scrutiny.

Seller Financing on the Sale

If the buyer of your old property wants you to carry a note instead of paying full price in cash, the seller-financed portion complicates the exchange. A promissory note from the buyer isn’t like-kind real property, so it counts as boot. The installment obligation is taxable to the extent of your gain, spread over the payment schedule under the installment sale rules.⁵

When a like-kind exchange is involved, the IRS adjusts the installment sale math: the contract price is reduced by the fair market value of the like-kind property you received, and the gross profit is reduced by the gain you deferred through the exchange.⁵ The result is that only the portion of gain attributable to the note gets reported as installment income over time. The note itself still generates taxable income that wouldn’t exist in a clean all-cash exchange.

The Deadlines That Kill Exchanges

Two deadlines govern every 1031 exchange, and both start the day you close on the sale. Miss either and there’s no grace period.

You have 45 days from the sale to identify potential replacement properties in writing. The identification must be signed by you and delivered to someone involved in the exchange, such as the Qualified Intermediary or the seller of the replacement. Sending it to your accountant, attorney, or real estate agent doesn’t count.⁶ The description needs enough specificity to identify the property clearly, such as a street address or legal description.

You then have 180 days from the sale to close on the replacement property. One catch trips people up: if your tax return is due before the 180 days are up, the return due date, including extensions, becomes your deadline instead.¹ Sell in October with a return due April 15, and you’ll need to file an extension to get the full 180 days. These deadlines cannot be extended except in a federally declared disaster.⁶

Financing is the most common way an exchange collapses. If your replacement loan doesn’t close in time, or if identified properties fall out of contract and you can’t line up an alternative, the whole thing fails.

What Happens If the Exchange Fails

If you miss the 45-day identification window or the 180-day closing window, the Qualified Intermediary returns the held funds to you after the exchange period expires, and the entire sale is treated as a standard taxable transaction. The tax lands in the year you originally sold.

You’d owe capital gains tax on the full appreciation, depreciation recapture at up to 25% on all previously claimed depreciation, and potentially the 3.8% Net Investment Income Tax.³⁴ State income tax may apply on top. If you hadn’t set aside funds for taxes because you expected the deferral, the cash crunch can be substantial. Building extra time into the financing timeline and identifying at least two viable replacement properties gives the best shot at closing on time.

Reporting the Exchange

Every 1031 exchange is reported on Form 8824, filed with your federal return for the year you transferred the old property.⁷ The form calculates the gain deferred and, if you received any boot, the gain you must recognize.⁸

You’ll report descriptions of both properties, dates of transfer and receipt, the relationship between the parties, exchange values, and the mortgage amounts on each side. The final accounting statement from your Qualified Intermediary supplies most of the numbers. If mortgage boot was recognized, the taxable gain flows to Schedule D and, where the thresholds are met, to Form 8960 for the Net Investment Income Tax. An exchange that spans two calendar years still gets reported on the return for the year you sold; you don’t wait for the replacement to close.

1
Office of the Law Revision Counsel. 26 USC 1031 – Exchange of Real Property Held for Productive Use or Investment
2
eCFR. 26 CFR 1.1031(j)-1 – Exchanges of Multiple Properties
3
Internal Revenue Service. Topic No. 409, Capital Gains and Losses
4
Internal Revenue Service. Net Investment Income Tax
5
Internal Revenue Service. Publication 537, Installment Sales
6
Internal Revenue Service. Like-Kind Exchanges Under IRC Section 1031
7
Internal Revenue Service. Instructions for Form 8824
8
Internal Revenue Service. About Form 8824, Like-Kind Exchanges