Cost segregation studies: the §1245 / §1250 reallocation framework, the engineering-based study requirement, the 100% bonus depreciation restoration under OBBBA, and the depreciation recapture trade-off

A cost segregation study is an engineering analysis that reallocates the depreciable basis of a real estate purchase or significant renovation among multiple depreciation categories. Without the study, the entire building cost defaults to either 27.5-year residential rental treatment under §168(c) or 39-year nonresidential commercial treatment, both as §1250 real property. With the study, components that qualify as §1245 personal property (carpeting, removable cabinetry, decorative lighting, dedicated electrical for business equipment, specialty plumbing for business use) get reallocated to 5-year or 7-year recovery periods, and components that qualify as §1250(c) land improvements (parking lots, sidewalks, landscaping, exterior lighting, signage) get reallocated to 15-year recovery.

The financial impact is substantial. A $5 million commercial property that defaults to 39-year depreciation generates roughly $128,000 per year of depreciation deduction. The same property with a cost segregation study reallocating 30% of basis to 5/7/15-year categories generates substantially more deduction in the first several years, particularly when combined with §168(k) bonus depreciation. For real estate investors with substantial properties or material income to absorb the deductions, the study often pays for itself many times over in the first year.

The framework was substantially affected by the One Big Beautiful Bill Act (OBBBA) signed July 4, 2025, which permanently restored 100% bonus depreciation for qualified property placed in service on or after January 20, 2025. The 2017 TCJA bonus depreciation had been phasing down (60% for 2024, 40% for 2025, 20% for 2026); the OBBBA restoration eliminates the phase-down and makes 100% bonus depreciation a stable planning assumption for the foreseeable future.

The legal framework

The statutory authority for the §1245 vs §1250 distinction is the Code itself, but the operational framework for cost segregation studies has been shaped by case law and IRS administrative guidance.

The seminal case is Hospital Corporation of America v. Commissioner, 109 T.C. 21 (1997), where the Tax Court applied pre-1981 investment tax credit (ITC) rules to distinguish §1245 personal property from §1250 real property. The IRS acquiesced to the HCA decision in 1999, and the ITC framework became the operational test for §1245 / §1250 classification.

The IRS Cost Segregation Audit Techniques Guide (ATG), most recently updated in Publication 5653, provides the operational framework that examiners use to evaluate cost segregation studies. The ATG identifies 13 specific quality elements that a defensible study should include, lists preferred and disfavored methodologies, and provides examples of properly classified vs. improperly classified components.

What §1245 vs §1250 means

The §1245 / §1250 distinction comes from the depreciation recapture provisions, but in cost segregation context, it operates as the dividing line between accelerated-recovery property and slow-recovery property.

§1245 personal property includes tangible personal property used in a trade or business, plus certain other property specified in §1245(a)(3). For real estate components, §1245 typically reaches:

Office furniture, fixtures, and equipment that are not structural components of the building.

Decorative elements (special wall coverings, decorative lighting that does not provide general illumination, decorative millwork that is not structural).

Dedicated electrical, plumbing, or mechanical systems serving specific business equipment (process piping, dedicated power for manufacturing equipment).

Carpeting, removable flooring, and similar components not integral to the building structure.

Movable partitions that are not load-bearing.

Specialty cabinetry and millwork in retail, restaurant, or medical environments.

Recovery periods for §1245 property are 5 years (most equipment), 7 years (office furniture), or other specified periods depending on the asset class under Rev. Proc. 87-56.

§1250 real property is buildings and their structural components: the building shell, structural elements, foundation, integrated HVAC for general building climate control, integrated electrical for general illumination, plumbing for general use, integrated security and fire suppression. Recovery period is 27.5 years for residential rental property or 39 years for nonresidential commercial property.

§1250(c) land improvements are improvements to land that are §1250 property but eligible for 15-year recovery: parking lots, sidewalks, landscaping, fencing, exterior lighting, signage. These are real property for purposes of the §1250 character analysis but get shorter recovery than the building shell.

What components typically get reallocated

A typical cost segregation study on a commercial property might reallocate the following:

Approximately 10-15% of basis to §1245 5-year property: carpeting, decorative lighting fixtures, removable cabinetry, dedicated electrical/mechanical serving specific business equipment.

Approximately 3-7% of basis to §1245 7-year property: office furniture, fixtures, and equipment that are part of the original purchase price.

Approximately 10-20% of basis to §1250(c) 15-year land improvements: parking lots, sidewalks, exterior lighting, landscaping.

The remaining 60-77% stays in 39-year (or 27.5-year for residential rental) §1250 real property.

The exact reallocation depends on the property type. Manufacturing facilities and medical buildings tend to have higher §1245 percentages because of specialized equipment-serving systems. Office buildings tend to have moderate reallocations. Apartment buildings and standard residential rental tend to have lower §1245 percentages because most components are integrated structural components of the building.

The ATG specifically cautions against "rule of thumb" reallocations (e.g., applying a flat 20% reduction to building basis as personal property without supporting analysis). These approaches do not meet the engineering-based study requirement and are vulnerable to disallowance on audit.

The required methodologies

The ATG identifies several acceptable methodologies, ranked roughly by IRS preference:

Detailed engineering from actual records. The gold standard. Uses construction invoices, contractor accounting records, and architect/engineer drawings to directly identify the cost of each component. Available primarily for newly constructed or recently renovated properties where the construction records are still accessible.

Detailed engineering cost estimate approach. Engineering-based study that uses estimated costs (from industry pricing databases like RSMeans, Marshall & Swift, or comparable resources) rather than actual cost records. Used for properties where actual cost records are not available; the engineering analysis still drives the classification, but the dollar allocations come from estimation.

Survey or letter approach. Asking the original contractor or developer for cost breakdowns. Less rigorous than the engineering approaches but acceptable when properly documented.

Residual estimation approach. Used in combination with another methodology; estimates the cost of certain components by subtracting other identified costs from the total. Acceptable as a supplement but not as the primary methodology.

Rule of thumb approach. The IRS explicitly disfavors flat-percentage allocations not supported by engineering analysis. The ATG warns that these studies are unlikely to survive audit scrutiny.

A "quality cost segregation report" per the ATG must include the methodology used, the basis for cost allocations, supporting documentation, qualifications of the preparer, and the specific component-by-component reallocation analysis.

The interaction with bonus depreciation

§168(k) bonus depreciation allows immediate expensing of a percentage of qualified property in the year placed in service. The interaction with cost segregation is substantial: cost segregation identifies §1245 property and shorter-life §1250(c) property; bonus depreciation then allows immediate expensing of much of that reallocated amount.

The history of the bonus depreciation rate:

2017 (post-TCJA): 100% for qualified property placed in service after September 27, 2017.

2018-2022: 100% (TCJA framework continued).

2023: 80% (phase-down began).

2024: 60%.

2025 (pre-OBBBA): 40% scheduled.

2025 (post-OBBBA, after January 20, 2025): 100% restored permanently.

2026 and forward: 100% (permanent restoration).

The OBBBA restoration is significant for cost segregation planning. Under the phase-down framework, the value of a cost segregation study was declining year over year because the bonus depreciation rate was declining. With 100% bonus depreciation permanently in place, the cost segregation study's value is restored to its 2017-2022 peak.

For a typical commercial property with 30% of basis reallocated to 5/7/15-year property and 100% bonus depreciation applied, the first-year deduction effectively includes 30% of the building basis in year one rather than spread across decades. For a $5 million property, that means $1.5 million of immediate deduction rather than the gradual depreciation over 39 years.

Look-back studies and Form 3115

Cost segregation studies are not limited to the year of acquisition. A "look-back" study can identify previously missed §1245 reallocations on a property that has been in service for several years, and catch up the missed accelerated depreciation through a Form 3115 (Application for Change in Accounting Method) filing.

The catch-up mechanism uses a §481(a) adjustment that allows the full cumulative accelerated depreciation to be claimed in a single year (the year of the change). For a property that has been depreciated under 39-year treatment for 5-7 years, a look-back study can identify substantial accumulated deductions that were missed and recover them in the year of the accounting method change.

The Form 3115 process requires:

Filing within the appropriate time window (generally with a timely-filed original return for the change year).

Identifying the specific accounting method change being made.

Including the §481(a) adjustment calculation.

Maintaining the supporting cost segregation study documentation.

The IRS generally provides automatic consent for the change from one depreciation methodology to another (the underlying §1245 vs §1250 classification doesn't require IRS approval; only the change in method does, and Rev. Proc. 2024-23 and similar guidance provide automatic consent procedures).

The depreciation recapture trade-off

The accelerated deduction from cost segregation comes with a corresponding recapture liability when the property is sold:

§1245 property is subject to ordinary income rate recapture on sale to the extent of the accumulated depreciation. For a property with substantial §1245 reallocation, the recapture can be material.

§1250 property gets §1250 unrecaptured gain at a maximum 25% rate, much more favorable than ordinary income rates.

§1250(c) land improvements are §1250 property and benefit from the 25% maximum rate.

The recapture trade-off matters most when a property is sold in the early years after acquisition. For a property held 3-5 years, the accelerated depreciation produces substantial current-year tax savings, but the recapture on sale claws back much of the benefit. For a property held 10+ years, the time value of money and the typically reduced recapture impact tilt the analysis strongly in favor of cost segregation.

The standard planning guidance: cost segregation is most valuable for properties held long-term or for properties where the investor wants to use accelerated depreciation to offset other current income, and is least valuable for short-hold strategies where the recapture quickly returns the deduction.

How cost segregation interacts with §1031 exchanges

Cost segregation interacts with §1031 like-kind exchanges in two ways:

When selling a property in a §1031 exchange, the accelerated depreciation taken on the property carries into the replacement property as deferred gain. The §1245 portion of the deferred gain remains §1245 character and is subject to ordinary income recapture if the replacement property is later sold outside a §1031 exchange.

A cost segregation study can be performed on the replacement property in a §1031 exchange, providing accelerated depreciation on the new property even though the original property's basis has been carried over.

The §1031 framework's general rule that "real property is like-kind to real property" works at the §1250 building level; the §1245 components technically would not be like-kind to each other under pre-2017 rules, but the TCJA limited §1031 to real property only, so §1245 personal property is no longer eligible for §1031 deferral in any event. For cost segregation purposes, this means the §1245 portion of the gain on a real estate sale must be recognized currently; it cannot be deferred through §1031.

Coordination with other small business provisions

Cost segregation operates in coordination with several other provisions in the Halstonberg small business pillar:

§179 immediate expensing is available for qualified §1245 property (not §1250). After a cost segregation study identifies §1245 components, §179 can be elected on those amounts up to the annual §179 cap ($1.16 million for 2026, phased out for businesses with substantial §179 property purchases).

§263(a) tangible property capitalization determines what costs must be capitalized vs. deducted as repairs in the first place. The interaction with cost segregation is that components that are capitalized under §263(a) can then be classified through cost segregation; components deducted as repairs are not capitalized and don't enter the cost segregation analysis.

§168 MACRS depreciation provides the recovery periods that cost segregation uses. The MACRS half-year, mid-quarter, and mid-month conventions apply to the reallocated amounts.

§199A QBI deduction is reduced by the cost segregation depreciation deductions for purposes of the QBI calculation. The interaction can be substantial for real estate investors whose QBI calculation depends on the W-2 wages and unadjusted basis limitations.

§1411 NIIT is reduced by passive activity depreciation deductions when the property is held in a passive activity. Cost segregation's accelerated depreciation flows through to reduce NIIT exposure for high-income investors.

Practical guidance

For real estate investors considering cost segregation:

The threshold question is whether the financial benefit justifies the study cost. Cost segregation studies typically cost $5,000 to $25,000 depending on property size and complexity. For properties under $1 million depreciable basis, the study may not produce enough first-year deduction to justify the cost. For properties over $5 million, the study almost always pays for itself many times over.

The OBBBA bonus depreciation restoration is a substantial benefit. Properties placed in service after January 20, 2025 qualify for 100% bonus depreciation; cost segregation on those properties produces immediate deductions much larger than under the phase-down framework.

Engineering-based methodology is essential. The IRS specifically disfavors rule-of-thumb studies; using a qualified cost segregation specialist with engineering credentials is the foundation of audit defense.

Look-back studies are available for previously-acquired properties. The Form 3115 accounting method change procedure allows missed accelerated depreciation to be recovered in a single year through the §481(a) adjustment.

Plan the recapture exposure. For properties expected to be sold within 3-5 years, model the ordinary income recapture on §1245 reallocations to ensure the net benefit remains positive.

For properties involving §1031 exchanges, the §1245 portion of accumulated depreciation must be recognized on sale; build this expectation into exchange planning.

Document the study and retain it for the entire holding period. The IRS can audit the depreciation positions established in the cost segregation study at any point during the property's ownership; the study documentation is the audit defense.

Cost segregation is a mature, well-established planning technique. The IRS has a clear framework for evaluating studies, the case law is settled at the high level, and the financial benefits are substantial. The execution is where the value is created or lost; using qualified specialists who follow the ATG quality framework is the difference between a defensible accelerated depreciation position and an audit exposure.