The debt replacement rule in a 1031 exchange is straightforward: the mortgage on your replacement property must equal or exceed the debt that was paid off on the property you sold. If the new loan is smaller, the difference is treated as taxable “mortgage boot” unless you cover the gap with your own cash at closing, dollar for dollar. Everything else about 1031 exchange debt replacement rules follows from that single requirement.
The mistake investors make is focusing only on matching sale price. You can reinvest every dollar of equity and still owe tax if your new financing falls short of your old financing. The IRS looks at debt separately, and the numbers have to work on both sides of the equation.
Why Paying Off Your Old Mortgage Counts as Money Received
When your sale closes and the buyer’s funds pay off your mortgage, federal tax law treats that debt relief as if the cash landed in your hands. Section 1031 is explicit that liabilities assumed by another party count as money received for purposes of calculating gain.1Office of the Law Revision Counsel. 26 USC 1031 – Exchange of Real Property Held for Productive Use or Investment The IRS calls the excess of debt relieved over debt assumed “mortgage boot,” and it triggers taxable gain the same way cash proceeds would.2Internal Revenue Service. Like-Kind Exchanges Under IRC Section 1031
A simple example: you sell a rental with a $500,000 mortgage and buy a replacement financed with a $300,000 mortgage. The $200,000 difference is mortgage boot. The IRS treats you as $200,000 richer, and you owe tax on that amount up to the total gain realized on the sale.
The lender, the loan type, and the interest rate don’t matter for this calculation. A conventional mortgage on the sold property can be replaced by a commercial loan, an SBA loan, or seller financing on the new one. What the IRS measures is the total dollar amount of liabilities. In a multi-property exchange, the math works on the aggregate: two sold properties with combined debt of $1.2 million against three replacement properties with combined financing of $1.3 million meets the requirement.
Covering a Shortfall With Outside Cash
When you can’t get enough new financing, the fix is to bring personal cash to the replacement closing. Treasury regulations allow cash paid by the taxpayer to offset liability relief, dollar for dollar.3eCFR. 26 CFR 1.1031(d)-2 – Treatment of Assumption of Liabilities If you had $600,000 in debt on the sold property and secured only $450,000 in new financing, wiring $150,000 of your own funds to the closing agent eliminates the mortgage boot.
The cash has to come from outside the exchange. Funds sitting with your qualified intermediary are exchange proceeds and are already spoken for in the equation. They cannot be redirected to plug the debt gap. What you need is personal savings, a portfolio loan, or funds from another source entirely.
The economics are usually favorable. Every dollar of outside cash you contribute increases your basis in the replacement property, which reduces the taxable gain when you eventually sell without another exchange. You’re not spending money to avoid tax; you’re choosing between paying tax today or building equity in the new asset.
Document the contribution carefully. Wire confirmations and closing statements showing the source of funds are what you’ll need for Form 8824 and what an auditor will ask to see.
The Netting Rule Only Runs One Way
Cash and debt do not offset each other symmetrically, and this is where deal structures fail. Treasury regulations create a one-way street: cash you pay can offset debt relief you receive, but debt you assume cannot offset cash you receive.3eCFR. 26 CFR 1.1031(d)-2 – Treatment of Assumption of Liabilities
Concretely:
- If the other party takes on $150,000 more in liabilities than you do, you can zero out that mortgage boot by contributing $150,000 in cash.
- If you receive $40,000 in cash but take on $70,000 more debt than you were relieved of, the extra debt does not cancel the cash boot. You still owe tax on the $40,000.
The regulation says it directly: “consideration received in the form of cash or other property is not offset by consideration given in the form of an assumption of liabilities,” while “consideration given in the form of cash or other property is offset against consideration received in the form of an assumption of liabilities.” In practical terms, you can throw cash at a debt problem, but you cannot borrow your way out of a cash problem. Investors who plan to take some cash off the table and compensate with a bigger new mortgage discover this at tax time.
Working Out the Recognized Gain
When boot exists, recognized gain is the lesser of the boot received or the total realized gain on the sale.1Office of the Law Revision Counsel. 26 USC 1031 – Exchange of Real Property Held for Productive Use or Investment Four steps get you there.
First, calculate realized gain. Sale price minus selling expenses gives the amount realized. Subtract adjusted basis, which is your original purchase price plus improvements minus accumulated depreciation. The result is your total realized gain.
Second, determine net debt relief. Subtract the debt assumed on the replacement property from the debt relieved on the sold property. If positive, that is mortgage boot. Then reduce it by any personal cash you contributed at closing.
Third, add up any cash you actually received from the exchange and the fair market value of any non-like-kind property you received. That total is cash boot, and remember, excess debt assumed cannot offset it.
Fourth, add mortgage boot (after cash offset) to cash boot. Recognized gain is the lesser of that combined total or your realized gain.
A worked example: you sell for $1,000,000, adjusted basis is $600,000, so realized gain is $400,000. The sold property had a $700,000 mortgage. You buy a replacement with a $600,000 mortgage and add no personal cash. Mortgage boot is $100,000. Because $100,000 is less than the $400,000 realized gain, recognized gain is $100,000 and you pay tax on that amount. Contribute $100,000 of outside cash at the replacement closing and mortgage boot goes to zero; the full $400,000 is deferred.
Reporting the Gain and Paying the Tax
Any boot you can’t eliminate is taxed in the year of the exchange. For investment real estate, expect two layers: unrecaptured depreciation taxed at a maximum federal rate of 25%, and long-term capital gains taxed at 0%, 15%, or 20% depending on income. The 3.8% net investment income tax may apply on top.
The exchange is reported on Form 8824. Line 15 captures cash received, the fair market value of non-like-kind property, and net liabilities assumed by the other party, reduced by exchange expenses.4Internal Revenue Service. Instructions for Form 8824 Recognized gain flows to Schedule D with your other capital gains and losses.5Internal Revenue Service. Instructions for Schedule D (Form 1040)
Reconcile Form 8824 against the closing statements before filing. The liability figures on the settlement sheets are what the IRS will compare to your return, and discrepancies are a common audit trigger for 1031 exchanges.
Refinancing to Adjust the Debt Picture
Refinancing looks like a way to manage the debt side of the exchange, and sometimes it is, but timing carries real risk. The IRS can apply the step transaction doctrine to collapse a refinance and an exchange into a single transaction if the two appear to be part of one coordinated plan to extract cash tax-free.
Refinancing Before the Sale
Pull cash out through a refinance shortly before selling in a 1031 exchange, and the IRS may recharacterize the refinance proceeds as disguised boot rather than genuine loan proceeds. Courts have looked past the formal structure to ask whether the transactions were prearranged and interconnected. The safest approach is to refinance well in advance of any exchange plans and put the proceeds to a real business purpose unrelated to the exchange. A refinance six months before a sale, with funds used to renovate a different property, reads very differently from one done two weeks before with proceeds sitting untouched in a bank account.
Refinancing After the Purchase
Refinancing the replacement property after closing is on firmer ground, but there is no bright-line safe harbor from the IRS. Most tax advisors recommend waiting at least six months to a year before pulling cash out to create clear separation between the exchange and the refinance. Closing on a replacement property with a large mortgage and immediately refinancing invites the same step transaction analysis. The longer the interval, and the more you can show you’ve been managing the property as an investment during that period, the harder the argument becomes.
How the Exchange Deadlines Affect Financing
The 1031 timeline puts real pressure on debt replacement. Two deadlines cannot be extended:
- You have 45 calendar days from the sale of the relinquished property to formally identify replacement properties in writing to your qualified intermediary.
- You must receive the replacement property within 180 days of transferring the relinquished property, or by the due date of your tax return (including extensions) for the year of the sale, whichever comes first.1Office of the Law Revision Counsel. 26 USC 1031 – Exchange of Real Property Held for Productive Use or Investment
Loan approvals, appraisals, and underwriting can consume the 180-day window fast. Start the loan process before your sale closes if you’re counting on new financing to match the old debt. A pre-approval in hand when you identify replacement property gives you a realistic chance of closing on time. If financing falls through on your identified property and you can’t close by day 180, the entire exchange fails and you owe tax on the full realized gain.
Which Debts Count Toward Replacement
Not every liability plays the same role. Debt secured by the sold property, like a traditional mortgage or deed of trust, is squarely within the exchange. When the closing pays it off, that is debt relief you must replace.
A line of credit secured by the sold property gets similar treatment. Even if the credit line funded something unrelated to the property itself, paying it off through the sale creates mortgage boot rather than cash boot, provided the debt was secured by the property and the sale agreement or QI agreement required its satisfaction at closing.
Unsecured debt is a different animal. You generally cannot use exchange proceeds to retire unsecured business debts, personal loans, or other obligations that aren’t tied to the sold property. Doing so risks being treated as constructive receipt of cash and can jeopardize the exchange’s tax-deferred status. Settle those obligations with separate funds outside the exchange.
Seller carryback notes create their own complication. A promissory note from the buyer is non-like-kind property, and if it’s made payable to you, it counts as taxable boot in the year of the exchange. The common workaround is to have the note made payable to the qualified intermediary and then contribute your own cash to the QI to buy the note back at face value, so the exchange funds can go toward the replacement while you personally hold and collect on the note. The assignment must happen at or before the relinquished closing; retroactive fixes don’t work.
The qualified intermediary sits at the center of these mechanics. The QI can use exchange funds to acquire replacement property and to pay off debt secured by the sold property, but cannot pay off unsecured debts and cannot release funds to you before the exchange is complete without triggering boot.6eCFR. 26 CFR 1.1031(b)-2 – Safe Harbor for Qualified Intermediaries That’s the reason cash used to fill a debt shortfall has to come from your own funds, not from the QI’s escrow.