A Section 1031 like-kind exchange defers gain on the sale of real property - but only to the extent the taxpayer receives qualifying like-kind property in return. Anything received that is not like-kind property is "boot" - and boot is taxable in the year of the exchange. Boot comes in two forms: cash boot (net cash or other non-like-kind property received) and mortgage boot (the net reduction in debt between the relinquished and replacement property). A taxpayer who understands boot can structure an exchange to be completely tax-free; a taxpayer who does not understand boot receives a tax bill they did not expect.
Cash boot: Any cash or non-like-kind property received in the exchange. If the exchange is structured correctly, the qualified intermediary holds all cash and no cash is released to the taxpayer until after closing. Cash released to the taxpayer triggers recognition. Net cash is computed across both legs of the exchange.
Mortgage boot (debt relief boot): When the replacement property has lower mortgage debt than the relinquished property, the taxpayer has been "relieved" of debt - and that relief is treated as cash received (boot). Example: relinquished property has a $500,000 mortgage; replacement property has a $300,000 mortgage. The $200,000 of debt relief is boot - fully taxable unless offset by cash added into the exchange.
Netting rule: Cash added to the exchange by the taxpayer offsets mortgage boot dollar-for-dollar. A taxpayer with $200,000 of mortgage boot who adds $200,000 of cash to buy up into the replacement property has zero net boot.
When boot is recognized, the tax character follows specific priority rules. Depreciation recapture under §1250 (unrecaptured Section 1250 gain at 25%) is recognized first, before any capital gain. If the amount of boot recognized is less than the total depreciation recapture that would have been triggered on a taxable sale, the entire boot is taxed at the 25% recapture rate. Only after all depreciation recapture has been recognized does remaining boot become long-term capital gain taxed at 0%, 15%, or 20% depending on the taxpayer's income.
Strategy 1 - Buy equal or greater debt: The most straightforward approach. Replace the relinquished property's $500,000 mortgage with a replacement property carrying at least $500,000 of debt. No mortgage boot triggered. The qualifying rule: replacement property debt (including new financing) must equal or exceed relinquished property debt.
Strategy 2 - Add cash to buy up: If the taxpayer cannot find replacement property with sufficient debt, they can add personal cash to the exchange equal to the mortgage boot amount. The cash addition offsets the debt relief. A taxpayer moving from $500,000 debt to $300,000 debt adds $200,000 of cash into the exchange to eliminate the $200,000 of mortgage boot.
Strategy 3 - Partial exchange with intentional boot: If some gain recognition is acceptable, the taxpayer can intentionally receive boot up to the amount of gain they want to recognize in the current year. This "partial exchange" defers the remaining gain. A taxpayer with $1 million of gain who wants to recognize $150,000 this year (for example, to use up net operating losses expiring) can receive $150,000 of boot intentionally and defer the remaining $850,000.
The replacement property's basis is calculated as: fair market value of relinquished property - deferred gain + gain recognized (boot taxed). Alternatively: basis of relinquished property - boot received + gain recognized. This stepped-down basis preserves the deferred gain in the replacement property - when the replacement property is eventually sold in a taxable transaction, the deferred gain is recognized along with any post-exchange appreciation.