What Is a Cost Segregation Study and When Does It Pay Off?

A building is not one asset for tax purposes. The IRS examiner handbook, the Cost Segregation Audit Technique Guide (Publication 5653, revised February 2025), explains that a purchase price contains land, land improvements, the building and its structural components, and section 1245 personal property, each with its own recovery period. A cost segregation study is the report that separates them and documents the cost of each. Below: what the study reclassifies, what the ATG says a quality study contains, the Form 3115 catch-up, recapture at sale, and when a study is worth ordering.

What a cost segregation study separates

The dividing line is whether an item is a structural component of the building (section 1250 real property, depreciated with the building) or tangible personal property (section 1245) that happens to be attached to it. The ATG traces that line through the investment tax credit regulations and case law such as Hospital Corporation of America v. Commissioner, 109 T.C. 21 (1997), which applied the old investment credit tests under MACRS. A study applies that analysis item by item and states the cost of each. The payoff comes from bonus depreciation: property with a recovery period of 20 years or less that was acquired after January 19, 2025 takes a 100% first-year allowance under IRC 168(k), while the building shell stays on 39-year (or 27.5-year) straight line.

What the IRS says a quality study contains

Chapter 4 of the ATG says there is no standard format, but that every study should classify assets into property classes, explain the rationale (with legal citations) for treating each as section 1245 or 1250 property, and substantiate each asset's cost basis while reconciling total allocated costs to total actual costs. It then lists 13 principal elements of a quality study:

Chapter 3 lists six approaches, from a detailed engineering approach built on actual cost records down to the “rule of thumb” approach that applies an industry-average percentage with little documentation; examiners are told to view that last one with caution. The guide also states that the IRS has not established requirements or standards for preparing studies, which cuts both ways: no format is mandatory, and the burden of substantiating each classification stays with the taxpayer.

Older buildings: catching up through Form 3115

A study is often ordered years after a building was placed in service. Chapter 6 of the ATG says a taxpayer may study previously existing property and recompute prior depreciation, but once a recovery period has been used on two or more consecutive returns it is an adopted method, and changing it means a Form 3115, not amended returns, which the guide says should generally be disallowed as a retroactive method change.

• The change. Section 6.01 of Rev. Proc. 2025-23, the current list of automatic changes, covers a change from an impermissible to a permissible method of depreciation for property the taxpayer owns at the beginning of the year of change. Its designated automatic accounting method change number is 7. The revenue procedure applies to Forms 3115 filed on or after June 9, 2025.
• The catch-up. The difference between depreciation taken and depreciation that the new classification would have allowed is a section 481(a) adjustment. Under section 7.03 of Rev. Proc. 2015-13, a negative adjustment (more deduction) is taken entirely in the year of change; a positive adjustment is spread over four years.
• The filing. The Form 3115 instructions require the original attached to the timely filed return (including extensions) for the year of change and a signed duplicate copy sent to the IRS in Ogden, Utah, or by fax, no later than the date the original is filed. The IRS does not acknowledge receipt.

Recapture when you sell

Reclassification changes the character of gain at sale. The components moved to 5-, 7- and 15-year classes are section 1245 property, and IRC 1245(a) taxes gain on them as ordinary income up to the depreciation taken, including bonus. The building portion remains section 1250 property: for straight-line depreciation held more than a year there is no ordinary recapture (Publication 544), and the depreciation-related gain is unrecaptured section 1250 gain taxed at a maximum 25% rate. A study therefore converts part of a future 25% gain into ordinary income at sale, in exchange for deductions now.

When a study tends to pay off

There is no dollar threshold in the law or the ATG. Four factors do the work:

• How much basis can move. A property with dedicated electrical, specialized plumbing, finishes, parking and landscaping has more to reclassify than a bare shell.
• Whether the deductions can be used this year. Rental activities are passive under IRC 469(c)(2). An individual deducts passive losses against other income only within the $25,000 allowance for actively managed rentals, which phases out by 50 cents per dollar of adjusted gross income above $100,000 (469(i)), or by meeting the real estate professional tests in 469(c)(7) (more than half of personal services and more than 750 hours in real property businesses, with material participation). An operating business that owns its building does not face that hurdle, though a large loss meets the limits in our NOL carryforward guide.
• Your marginal rate now versus at sale, and the holding period. The deduction saves tax at today’s rate; section 1245 recapture is taxed at ordinary rates later. A higher rate now and a long hold favor the study; a sale within a few years brings recapture quickly.
• Acquisition date and state law. Property acquired after January 19, 2025 gets 100% bonus; property under a contract signed earlier gets 20% for 2026, so the year-one effect is smaller. States that do not follow section 168(k) reduce the state-level benefit.

For a landlord depreciating a single house, the month-by-month schedule in our guide to rental property depreciation may be all that is needed; a study earns its fee on buildings with substantial personal property and owners who can use the deductions.

Sources: IRS, Cost Segregation Audit Technique Guide, Publication 5653 (Rev. 2-2025), chapters 2 to 6; 26 U.S.C. 168(c), (d), (e) and (k), recovery periods, conventions and bonus depreciation; IRS Rev. Proc. 2025-23, list of automatic changes, section 6.01 (change number 7); IRS Rev. Proc. 2015-13, section 7.03, section 481(a) adjustment period; IRS, Instructions for Form 3115 (Rev. December 2022), When and Where To File; 26 U.S.C. 1245, gain from dispositions of certain depreciable property; 26 U.S.C. 469(c)(2), (c)(7) and (i), passive activity rules for rental real estate; IRS Publication 946 (2025), How To Depreciate Property, Table A-7a; IRS Publication 527 (2025), Residential Rental Property, Table 2-1; IRS Publication 544 (2025), Sales and Other Dispositions of Assets. Rules, change numbers and percentages checked against these sources on September 26, 2026. This is general information, not tax advice for your situation. Tax services are provided by licensed tax professionals under a separate engagement agreement. BEG does not provide tax advice.