Cost Segregation After a 1031 Exchange: Carryover Basis, Excess Basis, and the Election That Changes Everything

Cost-seg on a §1031 replacement property is constrained by carryover-basis rules — by default only excess basis is bonus-eligible. The simplified-method election, the worked $1.8M example, and the §1245 recapture interaction.

Cost Segregation After a 1031 Exchange: Carryover Basis, Excess Basis, and the Election That Changes Everything

A property owner who closes a §1031 like-kind exchange and then orders a cost segregation analysis on the replacement property often discovers something uncomfortable at tax time: most of the basis is not bonus-eligible. The shortfall is not a mistake. It is the default rule under Treas. Reg. §1.168(i)-6, which governs how depreciation carries from a relinquished property into its replacement. The interaction between §1031 and cost segregation is one of the most misunderstood corners of real estate tax planning, and it is the difference between a six-figure first-year deduction and a five-figure one.

This article walks through how the carryover-basis rules limit bonus depreciation on a §1031 replacement, what the simplified-method election does, when it helps, when it hurts, and how the worked numbers actually shake out on a $1.2M-into-$1.8M exchange.

The §1031 Like-Kind Exchange in 90 Seconds

Under IRC §1031(a)(1), a property owner who exchanges real property held for productive use in a trade or business or for investment for other real property of like kind defers recognition of gain. The deferral is mechanical, not permanent — the deferred gain rides along inside the replacement property's basis and surfaces on a future taxable disposition.

Treas. Reg. §1.1031(a)-3 defines real property broadly enough to cover most fee-simple interests, leaseholds of 30 years or more, and certain inherently permanent structures. The qualifying property owner identifies a replacement within 45 days, closes within 180 days, and uses a qualified intermediary to avoid actual or constructive receipt of the relinquished proceeds.

The mechanic that drives everything in this article is basis. The replacement property does not get a fresh fair-market-value basis. It gets a carryover basis from the relinquished property, plus an excess basis if the property owner paid up. Cost segregation interacts with each piece differently.

Carryover Basis vs. Excess Basis (Treas. Reg. §1.168(i)-6)

Treas. Reg. §1.168(i)-6 is the rulebook for depreciating property received in a like-kind exchange. Its central distinction is between two layers of basis in the replacement property:

Carryover basis (sometimes called "exchanged basis"): the adjusted depreciable basis the property owner had in the relinquished property at the moment of exchange. This piece is treated as a continuation of the old depreciation schedule. The replacement property keeps the same recovery period, the same depreciation method, and the same convention as the relinquished property — as if nothing happened.

Excess basis: any additional cash, debt, or boot the property owner contributes to acquire the replacement above the FMV of the relinquished property. This piece is treated as a new asset placed in service on the date of the exchange. It gets its own recovery period, its own method, and — critically — its own first-year bonus depreciation eligibility.

In plain terms, the IRS lets the replacement property's basis ride for the carryover slice and start fresh for the excess slice. Cost segregation lives inside that distinction, because §1245 personal-property components and §1250 land-improvement components can only be peeled out of basis the property owner is allowed to redepreciate as new.

Default Treatment — Only Excess Basis Is Bonus-Eligible

Under the default rule of Treas. Reg. §1.168(i)-6, the carryover basis continues on its existing schedule. It cannot be reaccelerated. A property owner who has been depreciating a relinquished commercial building over 39-year straight-line cannot suddenly reclassify a slice of that carryover basis as 5-year personal property and run bonus on it. The carryover slice is locked in.

The excess basis, in contrast, behaves like a brand-new acquisition. A cost segregation analysis can identify the §1245 personal-property components (carpet, cabinetry, decorative lighting, certain electrical and plumbing serving specific equipment) and the §1250 land improvements (paving, fencing, landscaping, site lighting) inside the excess basis, and bonus depreciation under IRC §168(k) post-OBBBA §70301 applies to those components.

This default treatment is why a property owner who exchanges into a replacement at the same FMV as the relinquished property gets effectively zero bonus benefit from a feasibility estimate — there is no excess basis to work with. The whole replacement basis carries over, and carryover basis cannot be reclassified.

The default treatment is automatic. The property owner does nothing to elect it. It applies unless the property owner affirmatively makes the simplified-method election described in the next section.

The Simplified-Method Election — Combining Bases

Treas. Reg. §1.168(i)-6(i) gives the property owner a one-time choice on the return for the year of exchange: elect out of the default split-basis treatment and instead treat the entire replacement basis as a single new asset placed in service on the exchange date. This is commonly called the simplified-method election or the "elect-out" election.

The election produces a meaningfully different depreciation profile:

• The full replacement basis (carryover + excess) is treated as a new placed-in-service asset.
• A cost segregation analysis can carve §1245 and §1250 short-life components out of the entire basis, not just the excess slice.
• IRC §168(k) bonus depreciation applies to all eligible short-life components in the combined basis, subject to the post-OBBBA §70301 phase-out schedule that applies to the placed-in-service year.

The election is irrevocable for that exchange. The property owner makes it on the timely filed return (including extensions) for the tax year in which the replacement is placed in service. Once made, the relinquished property's prior depreciation schedule effectively ends, and a new clock starts.

The trade-off is real. Combining bases boosts upfront deductions but increases recapture exposure on a future disposition, because more of the replacement's basis is now classified as §1245 personal property — and §1245 recapture is taxed as ordinary income, not capital gain. The election is a cash-flow-now versus tax-character-later decision, and the right answer depends on the property owner's hold horizon, expected exit, and marginal rate.

Worked Example: $1.2M Relinquished, $1.8M Replacement

A worked example makes the difference concrete. Consider a property owner who exchanges:

• Relinquished property: $1.2M FMV, $200k adjusted depreciable basis, $300k mortgage debt at exchange.
• Exchange equity: $1.2M FMV minus $300k debt = $900k equity rolled into the replacement (net of selling costs, simplified for clarity). Of that, the qualified intermediary applies $700k as direct equity into the replacement closing in this scenario, with the remaining $200k absorbed by transaction costs and reserves.
• Replacement property: $1.8M FMV. Property owner takes on $400k of new debt at closing.

The basis arithmetic under Treas. Reg. §1.168(i)-6:

• Carryover basis: $200k. This is the relinquished property's adjusted depreciable basis. It rides into the replacement on the relinquished property's existing 39-year (or 27.5-year, depending on use) straight-line schedule.
• Excess basis: $1.8M replacement FMV minus $1.2M relinquished FMV = $600k. This is the new-asset slice.

Default Treatment Result

Under the default rule, only the $600k excess basis is bonus-eligible. Assume a feasibility estimate suggests roughly 25% of a typical commercial building's basis qualifies as §1245 personal property and §1250 land improvements with short recovery periods (5, 7, and 15 years).

• 25% of $600k = $150k of estimated short-life components.
• At a 60% bonus rate (illustrative for the placed-in-service year under the post-OBBBA §70301 schedule — verify the actual rate for the year), first-year bonus depreciation is $150k × 60% = $90k estimated.
• The remaining $450k of excess basis depreciates over 39-year straight-line (or 27.5-year if residential).
• The $200k carryover basis continues on the relinquished property's existing schedule, with no acceleration.

Estimated first-year deduction from the cost segregation analysis on the excess basis alone: roughly $90k, plus a partial year of straight-line on the long-life remainder.

Simplified-Method Election Result

Under the simplified-method election, the entire $1.8M replacement basis is treated as a new asset placed in service on the exchange date.

• 25% of $1.8M = $450k of estimated short-life components.
• At a 60% illustrative bonus rate, first-year bonus depreciation is $450k × 60% = $270k estimated.
• The remaining $1.35M depreciates over 39-year (or 27.5-year) straight-line, starting fresh.

Estimated first-year deduction from the cost segregation analysis under the election: roughly $270k, a $180k swing relative to the default. These are estimated round numbers — actual component percentages depend on the specific property, and the exact bonus rate depends on placed-in-service year.

The property owner pays for this acceleration on the back end. Of that $450k now classified as §1245 personal property in the replacement, every dollar of accumulated depreciation will be subject to §1245 recapture as ordinary income on a future taxable disposition. That is the trade.

Recapture Deferral Mechanics (§1245(b)(4))

IRC §1245(b)(4) is the bridge between §1031 and §1245. It says that a §1031 like-kind exchange does not trigger §1245 recapture at the moment of exchange, even though §1245 personal property has been transferred. Recapture is deferred, not eliminated.

The deferred recapture rides along inside the carryover basis of the replacement property. When the replacement is later sold in a taxable transaction, the §1245 recapture that would have hit the relinquished property surfaces — taxed as ordinary income to the extent of accumulated depreciation, capped at gain.

This is the structural reason the simplified-method election trades upfront benefit for back-end character risk. By electing in, the property owner converts a portion of carryover basis into newly classified §1245 components and runs accelerated depreciation on them. Every dollar accelerated becomes a dollar exposed to ordinary-rate recapture on disposition. Without the election, the carryover basis stays on its long-life schedule and accumulates less §1245 depreciation.

For a deeper dive on how §1245 recapture works mechanically, including the gain-cap and ordinary-rate interaction, see the §1245 recapture trap article.

When the Election Helps and When It Hurts

The simplified-method election is not a universal win. It is a hold-period and rate-arbitrage decision.

When the Election Tends to Help

• Long expected hold (10+ years). Time value of money on the upfront bonus deduction outweighs the back-end recapture, especially if the property owner expects to hold long enough to fully depreciate or to die holding the property (basis step-up under IRC §1014 wipes out recapture for the heirs).
• Plan to die holding (estate planning). The §1014 step-up at death eliminates §1245 recapture entirely. Maximize the upfront deduction.
• Plan to chain into another §1031 on exit. Recapture is again deferred under §1245(b)(4) on the next exchange. The upfront deduction is captured; the recapture keeps rolling.
• High current marginal rate, expected lower rate later. Front-load deductions at 37% federal; recapture later at a lower bracket if income drops in retirement.
• Excess basis is a small fraction of replacement FMV. When most of the replacement basis is carryover (e.g., trading $1.2M into $1.3M), the default rule produces a tiny first-year deduction. The election unlocks the full basis.

When the Election Tends to Hurt

• Short expected hold (under 5 years), taxable exit. Recapture surfaces fast at ordinary rates, eroding most of the upfront benefit.
• Property owner in a low current bracket, expected higher bracket later. Front-loaded deductions are worth less now than the recapture costs later.
• Excess basis is already most of the replacement FMV. The default rule already covers most of the property — the election adds the small carryover slice but accelerates recapture on it.
• Plan to sell to a non-related buyer in a taxable transaction within a few years. No §1014 step-up, no §1031 chain — full recapture exposure.

A feasibility-screening calculator can estimate the first-year deduction under both treatments for a property owner's specific facts. The calculator does not make the election decision — that requires a CPA or EA modeling the full hold-period economics, including expected disposition, marginal rates, and §1245 recapture exposure.

Run the long-hold scenario in the calculator to see estimated numbers for a 5+ year hold.

The 2017 TCJA Change: §1031 Limited to Real Property Only

Before the Tax Cuts and Jobs Act of 2017, IRC §1031 covered both real property and personal property. A property owner could exchange a piece of equipment, a vehicle fleet, or a fractional interest in artwork tax-free under §1031 the same way as real estate.

TCJA §13303 amended IRC §1031(a)(1) to limit like-kind exchange treatment to real property only, effective for exchanges completed after December 31, 2017. Personal property — including the §1245 components that cost segregation specifically peels out — no longer qualifies for §1031 deferral on its own.

The downstream consequence for cost segregation is significant and is covered in the next section.

Special Trap: §1245 Personal Property NOT Separately Rolled

Here is where the post-TCJA rules bite a property owner who has already cost-segregated a relinquished property.

Suppose the property owner cost-segregated the relinquished property years ago, peeling out (say) $200k of §1245 personal property — appliances, removable cabinetry, decorative lighting, specific-purpose electrical. That $200k has its own depreciation schedule, separate from the §1250 building shell.

Under TCJA §13303, those §1245 personal-property components do not qualify for §1031 deferral on their own. They are personal property, not real property. The exchange treats them as a deemed taxable disposition at the moment of the §1031 closing. The accumulated depreciation on those §1245 components hits as §1245 recapture in the year of exchange — at ordinary income rates, up to the realized gain on those components.

Practitioners sometimes overlook this. A §1031 exchange of a building with prior cost segregation does not automatically defer everything. The §1250 real-property components defer under §1031. The §1245 personal-property components recognize gain (and recapture) currently. The property owner ends up owing tax in the year of an exchange they thought was fully tax-free.

Treas. Reg. §1.1031(a)-3 reinforces the boundary by defining what counts as real property for §1031 purposes. Many components a cost segregation analysis has reclassified as §1245 personal property are explicitly excluded.

The practical implications:

• A property owner planning a §1031 exchange of a previously cost-segregated building should model the §1245 recapture impact before committing to the exchange. The deferred-tax assumption can be wrong by the §1245 component value.
• Aggressive cost segregation on a property the owner expects to §1031 in the near term can be counterproductive. Front-loaded deductions reverse as ordinary-rate recapture at the exchange.
• The post-TCJA regime favors keeping §1245 reclassifications modest when a §1031 exit is on the horizon — or holding to an estate step-up exit instead.

This is one of the most overlooked interactions in the post-2017 cost segregation landscape. It is also one of the most expensive to miss. For broader context on how the OBBBA bonus rates interact with these decisions, see the OBBBA bonus depreciation article. For recapture mechanics in general, see the recapture FAQ.

Run the Numbers

A property owner who has just closed a §1031 exchange — or is contemplating one — has three modeling questions: How much of the replacement basis is excess? What does the first-year deduction look like under the default rule versus the election? And what does the §1245 recapture exposure look like at expected disposition?

The calculator estimates the first-year deduction for both treatments based on the property owner's inputs, the placed-in-service year, and the post-OBBBA §70301 bonus schedule. It does not make the election decision and it cannot replace a CPA or EA who knows the full facts.

• Estimate the basic case for a 2026 placed-in-service replacement.
• Model a long-hold scenario where the election typically helps.
• Open the calculator to enter custom facts.

The output is a feasibility estimate the property owner takes to a qualified tax professional for the actual election analysis and return preparation.

Sources

• IRC §1031(a)(1) — Like-kind exchange of real property
• IRC §1245(b)(4) — Recapture deferral on like-kind exchanges
• IRC §168(k) post-OBBBA §70301 — Bonus depreciation schedule
• Treas. Reg. §1.1031(a)-3 — Definition of real property for §1031
• Treas. Reg. §1.168(i)-6 — Depreciation following an exchange
• Treas. Reg. §1.168(i)-6(i) — Simplified-method election
• TCJA §13303 (Pub. L. 115-97) — Real-property-only limitation effective post-2017

Disclaimer

Disclaimer. This article describes general federal tax concepts. TaxProtestTx (Nought Labs LLC) is a feasibility-screening tool, not tax advice or a cost segregation study. Calculator output cannot be relied on under Treasury Circular 230. Consult a qualified CPA, EA, or attorney before filing. Results are not guaranteed.