A cost segregation study is one of the most powerful tax strategies available to rental property owners. By reclassifying certain building components into shorter depreciation categories, you can accelerate tens or even hundreds of thousands of dollars in deductions into the first year of ownership. With the permanent restoration of 100% bonus depreciation under the One Big Beautiful Bill Act (OBBBA), cost segregation for rental properties has become even more valuable in 2025 and 2026.

What Is a Cost Segregation Study?

A cost segregation study is an engineering-based analysis that identifies and reclassifies components of a rental property into shorter depreciation recovery periods. Under the Modified Accelerated Cost Recovery System (MACRS), residential rental property is depreciated over 27.5 years using the straight-line method. Nonresidential (commercial) real property uses a 39-year recovery period.

However, many building components qualify as personal property or land improvements with much shorter recovery periods:

  • 5-year property: appliances, carpeting, certain electrical systems, plumbing fixtures dedicated to specific equipment, and window treatments
  • 7-year property: furniture, certain cabinetry, decorative fixtures, and specialized flooring
  • 15-year property: land improvements such as sidewalks, driveways, parking areas, landscaping, fencing, and exterior lighting

The IRS Cost Segregation Audit Techniques Guide provides detailed guidance on how these classifications work. The study typically involves an engineering team reviewing construction documents, blueprints, and the property itself to allocate costs to the correct asset classes.

How Bonus Depreciation Supercharges Cost Segregation

Cost segregation has always offered tax savings by shifting depreciation into earlier years. But the real game-changer is bonus depreciation under IRC Section 168(k).

Here is the recent history of bonus depreciation rates:

  • 2018 through 2022: 100% bonus depreciation under the Tax Cuts and Jobs Act (TCJA) for qualifying property
  • 2023: reduced to 80% under the TCJA phasedown schedule
  • 2024: reduced to 60%
  • January 1 through January 19, 2025: 40% under the original TCJA schedule
  • After January 19, 2025 (OBBBA): 100% bonus depreciation permanently restored for qualifying property acquired after this date

The OBBBA (P.L. 119-21), signed into law on July 4, 2025, permanently restored 100% bonus depreciation. This means all 5-year, 7-year, and 15-year property identified through a cost segregation study can be fully deducted in the year the property is placed in service, with no phasedown or expiration date.

Projected Tax Savings Example

Consider a rental property purchased for $500,000 (excluding land value). Without a cost segregation study, the entire depreciable basis is spread over 27.5 years using straight-line depreciation, producing roughly $18,182 in annual depreciation.

With a cost segregation study, a qualified engineer might reclassify 20% to 40% of the building cost into 5-year, 7-year, or 15-year property. Under current law with 100% bonus depreciation, those reclassified components are deducted entirely in year one. For a $500,000 property where 30% ($150,000) is reclassified:

  • Year-one depreciation without cost segregation: approximately $18,182
  • Year-one depreciation with cost segregation: approximately $150,000 (reclassified components via bonus depreciation) plus roughly $12,727 in straight-line depreciation on the remaining $350,000 of 27.5-year property
  • Total first-year deduction with cost segregation: approximately $162,727

The exact savings depend on your marginal tax bracket, the specific allocation determined by the study, and the month the property is placed in service (residential rental property uses the mid-month convention).

Passive Activity Loss Rules and Cost Segregation

Rental real estate activities are generally classified as passive activities under IRC Section 469, which limits your ability to deduct rental losses against other income. Understanding these rules is essential before committing to a cost segregation study, because the large first-year deduction it generates may be partially or fully suspended.

There are two important exceptions under IRS Publication 925:

  • $25,000 special allowance: if you actively participate in a rental real estate activity, you can deduct up to $25,000 of passive rental losses against nonpassive income. This allowance phases out between $100,000 and $150,000 of modified adjusted gross income (MAGI).
  • Real estate professional status: if you spend more than 750 hours per year in real property trades or businesses in which you materially participate, and more than half of your total personal services are in those real property activities, your rental real estate activities are not treated as passive. This allows you to deduct the full cost segregation benefit against your other income, including W-2 wages.

If the cost segregation deduction exceeds what you can use in the current year, the suspended losses carry forward and offset future rental income or are released when you dispose of the property.

Section 179 and Cost Segregation

In addition to bonus depreciation, Section 179 allows businesses to expense qualifying property in the year it is placed in service. The OBBBA raised the Section 179 deduction limit to $2,500,000 for 2025 (indexed to $2,560,000 for 2026), with a phase-out threshold starting at $4,000,000 ($4,090,000 for 2026).

Section 179 applies to certain tangible personal property used in a rental activity, though it does not apply to the residential rental building itself. For rental property owners, bonus depreciation typically provides the primary benefit, while Section 179 may apply to specific qualifying items such as appliances, HVAC equipment, or security systems used in the rental business.

Look-Back Studies for Existing Properties

You do not need to have recently purchased a property to benefit from cost segregation. Owners who acquired rental properties in prior years can perform a "look-back" cost segregation study and claim the missed depreciation through a change in accounting method using IRS Form 3115.

This approach allows you to claim all of the catch-up depreciation in a single tax year without amending prior returns. It is especially valuable for property owners who placed assets in service during the 2023 or 2024 phasedown period and never performed a study, as well as for owners of properties acquired years ago who have been depreciating the entire basis over 27.5 years.

Depreciation Recapture: What Happens When You Sell

When you eventually sell a rental property that has benefited from cost segregation, you will face depreciation recapture. Under IRC Section 1250, depreciation on the building portion is recaptured at a maximum rate of 25% (to the extent of unrecaptured Section 1250 gain). Personal property components reclassified through cost segregation are recaptured as ordinary income under Section 1245.

This does not eliminate the benefit of cost segregation. It shifts income recognition to the year of sale, and the time value of the accelerated deductions typically outweighs the recapture. Rental property owners considering a 1031 exchange can defer both capital gains and depreciation recapture entirely by exchanging into a like-kind property.

Who Should Consider a Cost Segregation Study?

A cost segregation study for a rental property is typically most beneficial when:

  • The depreciable basis of the property (excluding land) is $500,000 or more
  • You have recently purchased, constructed, or substantially renovated a rental property
  • You qualify as a real estate professional or have passive income from other sources to offset
  • You are planning to hold the property for several years (not flipping)
  • You own properties from prior years that were never studied (look-back opportunity)

Even properties below the $500,000 threshold can benefit, especially with desktop or in-house cost segregation methods that carry lower fees than full engineering studies.

Cost Segregation and Arizona Rental Properties

Arizona rental property owners should be aware of a few state-level considerations. Arizona conforms to federal depreciation rules for income tax purposes, so the accelerated depreciation from a cost segregation study flows through to your Arizona Form 140 return. Arizona's flat 2.5% individual income tax rate means the state tax savings are more modest than the federal benefit, but they still add to the overall return on investment.

Note that Arizona transaction privilege tax (TPT) on residential rentals was repealed effective January 1, 2025, so rental income is no longer subject to TPT in most jurisdictions. However, commercial rental properties remain subject to city-level TPT, which is a separate consideration for investors with mixed portfolios.

Frequently Asked Questions

How much does a cost segregation study cost?

Fees vary based on the property size, complexity, and the provider. Full engineering-based studies for larger properties may range from $5,000 to $15,000 or more. Desktop or software-driven studies for smaller properties can cost significantly less. The study typically pays for itself many times over through the tax savings generated.

Can I do a cost segregation study on a property I already own?

Yes. A look-back study allows you to claim missed accelerated depreciation on properties acquired in prior years. The catch-up deduction is claimed in the current year through IRS Form 3115 (change in accounting method), with no need to amend prior returns.

Does cost segregation work for residential rental property only?

No. Cost segregation studies apply to both residential rental property (27.5-year property) and commercial or special-use properties such as medical practices (39-year property). The benefit can be even greater for commercial properties due to the longer baseline recovery period.

What if my rental losses are limited by the passive activity rules?

Suspended passive losses carry forward to future tax years and offset rental income or other passive income. If you dispose of your entire interest in the rental activity in a fully taxable transaction, all accumulated suspended losses are released and deducted in the year of sale.

Is bonus depreciation really permanent now?

Yes. The One Big Beautiful Bill Act (OBBBA), signed July 4, 2025, permanently restored 100% bonus depreciation for qualifying property acquired after January 19, 2025. There is no phasedown or sunset date under current law.

How K&R Strategic Partners Can Help

At K&R Strategic Partners, we help rental property owners maximize their tax savings through cost segregation and strategic tax planning. Our team can assist with identifying properties that are strong candidates for a study, coordinating with qualified cost segregation firms for larger projects, handling the depreciation calculations and Form 3115 filings for look-back studies, and integrating cost segregation into your broader tax planning strategy.

If you invest in rental real estate, we encourage you to schedule a consultation to discuss your most tax-efficient options. Please have a copy of the settlement statement from the purchase of your rental property available when we meet.