Modeling the 1031: Boot, Basis Carryover, and Deferred Gain

Why the Math Matters

Every 1031 exchange produces a specific numerical result: how much gain was deferred, how much was recognized (taxed), what the new property's depreciable basis is, and how that basis gets depreciated going forward. These aren't academic questions. They determine the after-tax IRR of the replacement property, the depreciation deductions available to offset operating income, and the embedded tax liability that will eventually come due — whether at the next disposition, a partnership dissolution, or death.

Most practitioners understand the concept of boot (the taxable portion) and basis carryover (the reduced depreciable basis). Far fewer can model it correctly in a pro forma. The errors compound: an incorrect basis flows into an incorrect depreciation schedule, which produces an incorrect after-tax cash flow, which generates an incorrect IRR. An institutional fund reporting a 12.5% net IRR to its LPs may actually be delivering 11.2% once the embedded deferred gain is properly accounted for.

This article covers the formulas, the bifurcation mechanics, and how to wire them into a disposition waterfall. Every number is real and scalable.

Boot Calculation

Boot is the non-like-kind consideration received in an exchange — anything the exchanger gets that isn't qualifying real property, as defined in IRC Section 1031(b). Boot is taxable to the extent of the realized gain. There are two components:

Cash boot

Cash boot is exchange proceeds not reinvested in the replacement property. If you sell for $40M, net $38.5M after closing costs, and reinvest $35M in the replacement property, the $3.5M difference is cash boot.

Formula: Cash Boot = Net Exchange Proceeds – Cash Invested in Replacement Property

Mortgage boot

Mortgage boot arises when the debt on the relinquished property exceeds the debt on the replacement property. Debt relief is treated as boot received. If you pay off a $20M mortgage on the relinquished property and take on only a $15M mortgage on the replacement, the $5M difference is mortgage boot.

Formula: Mortgage Boot = max(0, Debt Relieved – Debt Assumed)

Critically, mortgage boot can be offset by adding cash. If you owe $20M on the relinquished property and assume only $15M on the replacement, you can add $5M of additional cash to eliminate the mortgage boot. The IRS nets cash contributed against debt relief — but only in one direction, as established in Treasury Regulation 1.1031(j)-1. Cash boot and mortgage boot do not offset each other. You cannot use excess debt assumption to offset cash boot.

Total taxable boot

Formula: Total Boot = Cash Boot + Mortgage Boot (each calculated independently, each floored at zero)

Boot is taxable to the extent of the realized gain. If your total realized gain is $18M and your total boot is $5M, you recognize $5M of gain. If your boot exceeds your gain (unusual but possible in low-gain scenarios), you recognize gain only up to the gain amount — boot cannot create a loss.

Basis Carryover and Excess Basis

The replacement property's tax basis is not its purchase price. Under IRC Section 1031(d) and Treasury Regulation 1.1031(d)-1, the basis carries over from the relinquished property, adjusted for boot and gain recognized. This produces a basis that is lower than the amount paid — sometimes substantially lower after serial exchanges.

The formula

Replacement Property Basis = Purchase Price – Deferred Gain + Boot Paid (if any) – Boot Received

Equivalently — and this is the formulation most useful for modeling — the replacement basis can be decomposed into two components:

• Carryover basis: Equal to the adjusted basis of the relinquished property at the time of exchange. This represents the "old" investment that carries forward.
• Excess basis: Equal to any new investment above the relinquished property's equity. If you put in more cash, assumed more debt, or otherwise invested more than your equity in the old property, the additional amount creates new basis.

Total Replacement Basis = Carryover Basis + Excess Basis

Worked example

Relinquished property: purchased for $25M, accumulated depreciation $8M, adjusted basis $17M, sold for $40M less $1.5M closing costs = $38.5M net. Realized gain = $38.5M – $17M = $21.5M.

Replacement property: purchased for $35M. Boot received: $3.5M (from the prior example). Gain recognized: $3.5M (boot is taxable to the extent of gain, and gain exceeds boot).

Deferred gain: $21.5M – $3.5M = $18M.

Replacement basis: $35M – $18M = $17M. Note that this equals the carryover basis — the adjusted basis of the relinquished property. That's not a coincidence. In a partial exchange where boot is the only difference, the carryover basis exactly equals the old adjusted basis.

If the exchanger had invested $5M more cash to acquire a $40M replacement property (no boot), the replacement basis would be: $40M – $21.5M = $18.5M. The $1.5M above the carryover basis is excess basis — new investment that gets its own depreciation schedule.

Deferred Gain Tracking

Institutional portfolios often contain properties that have been through two, three, or more sequential 1031 exchanges. Each exchange compounds the deferred gain and reduces the basis further. Tracking this is essential for three reasons:

1. The deferred gain is an embedded liability. It comes due when the property is eventually sold in a taxable transaction — Section 1031 defers recognition, it does not eliminate it, as IRS Publication 544 (Sales and Other Dispositions of Assets) makes explicit. A property with $30M of cumulative deferred gain carries an embedded tax liability of roughly $7.5M-$9M (depending on rates and recapture), which must be factored into any disposition analysis.
2. LP reporting requires it. Fund managers must disclose the deferred gain to limited partners, who need it for their own tax planning and basis tracking. A K-1 that doesn't properly reflect cumulative deferred gains exposes the GP to audit risk.
3. Exit strategy depends on it. A property with $40M of deferred gain may never be sold in a taxable transaction — the fund will exchange it again, contribute it to an UPREIT via Section 721, or hold it until the partners can take advantage of the stepped-up basis at death under IRC Section 1014. The size of the deferred gain drives the exit strategy.

Serial exchange example

Exchange 1: Buy Property A for $10M. Sell for $20M (adjusted basis $7M, gain $13M). Exchange into Property B for $20M. Property B basis: $20M – $13M = $7M.

Exchange 2: Sell Property B for $35M (adjusted basis after depreciation: $5M, gain $30M). Exchange into Property C for $35M. Property C basis: $35M – $30M = $5M.

Property C was purchased for $35M but has a tax basis of $5M and an embedded deferred gain of $30M. The depreciable basis (excluding land) is roughly $4M — on a property that a market buyer would depreciate at $28M. The depreciation differential alone is worth approximately $670K per year in after-tax cash flow (assuming a 39-year life, 37% combined federal/state rate).

Post-Exchange Depreciation

The replacement property's depreciable basis is not a single number on a single schedule. After a 1031 exchange, depreciation is bifurcated into two components that follow different rules:

Carryover basis depreciation

The carryover basis — the portion equal to the relinquished property's adjusted basis — continues depreciating on the relinquished property's remaining useful life, using the same method and convention. If the relinquished property was a 39-year commercial building placed in service 12 years ago, the carryover basis has 27 years of remaining life. The depreciation schedule doesn't reset.

This means acquiring a replacement property through a 1031 exchange produces less annual depreciation than acquiring the same property in a taxable purchase. A market buyer would start a fresh 39-year schedule on the full purchase price (less land). The exchange buyer continues the old schedule on the lower carryover basis.

Excess basis depreciation

If the exchanger invested more than the relinquished property's equity — additional cash, higher debt — the excess creates new basis that starts a fresh depreciation schedule. The excess basis is depreciated as if the replacement property were newly placed in service: 39 years for commercial real property, 27.5 years for residential rental property, using the applicable method and convention.

Example

Relinquished property: commercial office, 39-year life, placed in service 15 years ago. Original cost basis (improvements only): $20M. Accumulated depreciation: $7.7M. Adjusted basis (improvements): $12.3M. Remaining life: 24 years.

Replacement property: purchased for $35M. Land allocation: 20% ($7M). Improvements: $28M. Exchange with no boot — full deferral.

Carryover basis (improvements): $12.3M, depreciated over remaining 24 years = $512,500/year.

Excess basis (improvements): $28M – $12.3M = $15.7M, depreciated over 39 years = $402,564/year.

Total annual depreciation: $915,064.

Compare to a market buyer: $28M ÷ 39 years = $717,949/year. Wait — the exchange buyer actually gets more depreciation in this case because the carryover basis is being depreciated over a shorter remaining life (24 years vs. 39). This isn't always the case, but it illustrates why the calculation matters: the result depends on the specific numbers, not a rule of thumb.

Boot as a Decision Variable

Most 1031 guidance treats boot as something to avoid. That framing is incomplete. Boot is a decision variable — sometimes taking boot is the right economic answer.

Consider a fund that sells a $40M property with $18M of deferred gain. The acquisitions team identifies a $35M replacement that meets all investment criteria and a $42M replacement that is marginally acceptable but would fully match value and avoid boot. The $42M property trades at a 5.2% cap rate versus the target's 5.8%.

Taking $5M of boot on the $35M acquisition triggers roughly $1.25M in federal capital gains tax (at 25% blended rate including recapture). But overpaying $7M for the $42M property to avoid that $1.25M tax destroys $5.75M of value. The tax-efficient answer is to take the boot.

The framework: compare the tax cost of boot against the economic cost of avoiding it. If avoiding boot requires overpaying for a replacement property, accepting a lower-quality asset, or rushing into a deal before the 45-day deadline, the boot may be cheaper than the alternative.

Common Mistakes

• Using purchase price as depreciable basis. The most common error in post-exchange pro formas. The replacement property's depreciable basis is the carryover basis plus excess basis — not the purchase price. A $35M acquisition with a $17M basis generates roughly half the depreciation that a $35M taxable purchase would. If your model shows full depreciation on the purchase price, every after-tax metric is wrong.
• Netting cash boot against mortgage boot. Cash boot and mortgage boot are calculated independently. Excess debt assumption does not offset cash boot. You can offset mortgage boot by contributing additional cash, but you cannot offset cash boot by assuming more debt. This asymmetry trips up even experienced practitioners.
• Ignoring depreciation bifurcation. After the exchange, the carryover basis and excess basis must be depreciated on separate schedules with different remaining lives. Lumping them together on a single 39-year schedule produces incorrect depreciation in every year of the hold period.
• Forgetting that closing costs reduce boot. Certain closing costs paid by the exchanger reduce the amount of boot. Brokerage commissions, transfer taxes, and QI fees paid from exchange proceeds reduce cash boot. This is favorable — it means less taxable boot — but many models don't capture it, overstating the tax liability.
• Not tracking cumulative deferred gain across serial exchanges. Each exchange adds to the deferred gain. A property that has been through three exchanges may carry $40M+ of deferred gain that will come due at the next taxable event. If the portfolio manager doesn't track this, exit strategy analysis is based on incomplete information.
• Treating the exchange as tax elimination rather than tax deferral. Section 1031 defers gain — it doesn't eliminate it. The deferred gain is embedded in the replacement property's basis and will be recognized at the next taxable disposition (unless the property is exchanged again, contributed under Section 721, or held until death for a stepped-up basis under Section 1014). Data from Mountain Dell Consulting estimates that over $100 billion in annual exchange volume relies on this deferral mechanism, underscoring the scale at which this distinction matters. Modeling an exchange as a permanent tax benefit overstates the after-tax return.
• Neglecting cost segregation on excess basis. The excess basis component of a replacement property is eligible for a cost segregation study, which can accelerate depreciation by reclassifying components to shorter recovery periods (5, 7, or 15 years). The carryover basis retains its original classification. Missing this opportunity leaves depreciation deductions on the table.

How to Model It

A 1031 exchange model needs to flow from the disposition through the exchange and into the replacement property's operating pro forma. Here's what each section requires:

Disposition tab

Sale price, closing costs (brokerage, transfer tax, legal), net proceeds to QI, adjusted basis of relinquished property (original cost less accumulated depreciation), realized gain, Section 1250 recapture amount (accumulated depreciation, taxed at 25% per IRC Section 1250(a)), and remaining capital gain (taxed at 20% plus 3.8% Net Investment Income Tax under IRC Section 1411 for applicable taxpayers). The exchange must be reported on IRS Form 8824 (Like-Kind Exchanges) attached to the taxpayer's return for the year of the relinquished property transfer.

Exchange tab

Net proceeds from QI, debt relieved on relinquished property, cash boot calculation, mortgage boot calculation (with offset logic), total boot, gain recognized (lesser of total boot and realized gain), deferred gain, replacement property basis calculation (purchase price minus deferred gain), and basis bifurcation (carryover vs. excess).

Replacement property depreciation tab

Two depreciation schedules running in parallel: carryover basis on the relinquished property's remaining life, excess basis on a fresh recovery period. Land allocation applied to total basis (not purchase price). The tab should show annual depreciation from each component and the combined total, year by year, for the projected hold period.

After-tax cash flow tab

NOI, debt service, before-tax cash flow, depreciation (from the bifurcated schedule), taxable income, tax liability, after-tax cash flow. The embedded deferred gain should be modeled as a contingent liability in the disposition year — either as a future tax at the expected exit or as a present-value adjustment to current-period returns.

The test of a good 1031 model: change the relinquished property's accumulated depreciation and watch the replacement property's after-tax IRR recalculate. If it doesn't — if the depreciation schedule and basis don't update — the formulas aren't properly linked.

Related Articles

This article is part of the 1031 exchange series. Each article covers a specific aspect of exchange structuring for institutional CRE portfolios:

• 1031 Exchange Mechanics — The 45-day and 180-day deadlines, three identification rules, and like-kind requirements post-TCJA.
• Reverse Exchanges — EAT/QEAA structures, Rev. Proc. 2000-37 safe harbor, and improvement exchanges at institutional scale.
• DST Replacement Property — When and how to use DST interests as identification backstops and passive replacement vehicles.
• 721 Exchange / UPREIT — Contributing exchanged property into a REIT operating partnership for liquidity and diversification.