To apply cost segregation on your tax return, you report the reclassified asset categories from your engineering study on IRS Form 4562 for the year the property is placed in service, and, if you’re applying the study to a property you’ve already been depreciating, you file Form 3115 to change your accounting method and claim a Section 481(a) catch-up adjustment on the current-year return. Which form you need turns on that single question: is this the first year the building is on your books, or have you owned it for a while?
What the Study Gives You to Put on the Return
Every number that lands on your forms comes from the cost segregation study report. A qualifying study reallocates the building’s cost basis into four categories under the Modified Accelerated Cost Recovery System:1Internal Revenue Service. Publication 946 – How To Depreciate Property 5-year and 7-year personal property (specialty lighting, carpeting, certain plumbing fixtures, cabinetry), 15-year land improvements (parking lots, sidewalks, fences, landscaping), 27.5-year or 39-year real property for the structural shell, and non-depreciable land.2Internal Revenue Service. Topic No. 704, Depreciation Residential rental uses 27.5 years; commercial uses 39. Indirect costs like architectural and engineering fees are allocated proportionally across the categories.
The report should document methodology, list each reclassified asset, and give you the dollar amounts that flow onto the tax forms. Keep it permanently. The IRS Cost Segregation Audit Techniques Guide is what examiners use when they review these claims,3Internal Revenue Service. Audit Techniques Guides so the study needs to meet those standards before you rely on it.
Reporting a Current-Year Property on Form 4562
For property placed in service during the current tax year, each asset category from the study gets its own line on Form 4562, Depreciation and Amortization.4Internal Revenue Service. Instructions for Form 4562 (2025) For each line you enter the depreciable basis, the recovery period (5, 7, 15, 27.5, or 39 years), and the applicable MACRS convention.
The convention controls how much depreciation you take in year one. The half-year convention is the default and treats assets as placed in service at the midpoint of the year. If more than 40% of your total MACRS property placed in service during the year went in during the last three months, you must switch to the mid-quarter convention instead.4Internal Revenue Service. Instructions for Form 4562 (2025) Residential rental and nonresidential real property are excluded from that 40% test, but the personal property your study reclassifies is not, so a large late-year acquisition can pull you into mid-quarter territory.
The Bonus Depreciation Line
Under the One Big Beautiful Bill Act signed into law on July 4, 2025, 100% bonus depreciation has been permanently restored for qualified property acquired after January 19, 2025. MACRS property with a recovery period of 20 years or less qualifies, which covers every category a cost segregation study reclassifies except the building shell itself. In practice, that means the 5-year, 7-year, and 15-year assets from the study can be written off entirely in the placed-in-service year rather than spread across their recovery periods.
Bonus depreciation goes in the special depreciation allowance section of Form 4562. The amount equals the full cost basis of each qualifying asset. Unlike a Section 179 election, bonus depreciation has no annual dollar cap and can create or increase a net operating loss. On a $2 million commercial building where the study identifies $500,000 in short-lived assets, the first-year deduction is $500,000 rather than $12,820 spread over 39 years.
Applying the Study to a Property You Already Own
If you’ve owned the building for one or more years and have been depreciating it as a single 27.5-year or 39-year asset, you can’t simply switch to the new schedule going forward. Reclassifying assets into shorter recovery periods is a change in accounting method, and the IRS requires Form 3115, Application for Change in Accounting Method.5Internal Revenue Service. About Form 3115, Application for Change in Accounting Method
Cost segregation reclassification is an automatic consent change, so you don’t request permission in advance. The general procedures live in Revenue Procedure 2015-13, and the current list of qualifying automatic changes is in Revenue Procedure 2024-23. File the form with your return and the IRS processes it without a separate approval step, provided you follow the procedural requirements.
The Section 481(a) Catch-Up Adjustment
Rather than amending every prior return, Section 481(a) lets you capture all the depreciation you missed in a single current-year adjustment.6Office of the Law Revision Counsel. 26 U.S. Code 481 – Adjustments Required by Changes in Method of Accounting You calculate the total depreciation actually claimed under the old method, subtract it from what you would have claimed using cost segregation from the start, and report the difference on the current-year return.
The number is often substantial. A commercial building purchased five years ago for $3 million might have $600,000 to $800,000 in reclassifiable assets, and the cumulative difference can easily produce a six-figure current-year deduction. If the adjustment creates a net operating loss, that NOL carries forward indefinitely and can offset up to 80% of taxable income in future years under current law.
Filling Out the Form
Form 3115 asks you to describe the property, your current depreciation method, and the proposed method based on the study. It requires the Section 481(a) adjustment amount broken down by asset class. Your cost segregation report should supply these figures directly; the specialist calculates the cumulative adjustment as part of the deliverable. Cross-check the numbers against prior returns and the study before filing. An overstated adjustment produces an underpayment if the IRS later disallows part of the reclassification, and that brings penalties and interest.
Filing Mechanics and the Duplicate Copy
Form 4562 attaches to your timely filed federal income tax return for the year the property is placed in service or the year you implement the study. If you’re filing Form 3115, both forms travel with the return. Electronic filing through standard tax software is the common route and produces the fastest processing.
Form 3115 has one extra step that trips people up: you must file a duplicate copy with the IRS national office at the same time you file your return. The duplicate goes to the IRS in Ogden, Utah, by mail or private delivery, with a fax option as an alternative.7Internal Revenue Service. Where To File Form 3115 Missing the duplicate doesn’t automatically invalidate the method change, but it creates a procedural deficiency the IRS can flag.
Electronic filers usually see processing confirmation within a few weeks. Paper returns typically take six weeks or longer.8Internal Revenue Service. Refunds Complex commercial returns with Form 3115 attached sometimes draw additional review, so a longer wait isn’t necessarily a problem.
Passive Activity Rules Can Cap What You Actually Deduct
Generating a large depreciation deduction doesn’t mean you can use it all this year. If the property is a rental and you don’t qualify as a real estate professional, the loss is passive and can only offset passive income.9Office of the Law Revision Counsel. 26 USC 469 – Passive Activity Losses and Credits Limited This is the single biggest limitation on cost segregation for individual investors.
For most W-2 employees who own rental property on the side, unused passive losses carry forward until you generate passive income or sell the property. A narrow exception allows up to $25,000 in rental losses against active income if your adjusted gross income is below $100,000, phasing out completely at $150,000.
Real estate professional status is the way around the limit. You must 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 across all businesses must be in real estate.10Internal Revenue Service. Publication 925 (2025), Passive Activity and At-Risk Rules Hours as an employee don’t count unless you own more than 5% of the employer, which makes the threshold essentially unreachable for a full-time W-2 worker. If you can’t clear it, the study still has value because the deductions aren’t lost, just deferred.
Investors in partnerships, S corporations, and other pass-throughs face these limits at the individual level: the entity reports the depreciation, the deduction flows through, and each owner independently has to satisfy the passive activity rules to use it against non-passive income. The excess business loss limitation, which caps total business losses an individual can claim in a single year (adjusted annually for inflation), sits on top of the passive rules. Losses exceeding that cap convert to NOL carryforwards.
What Happens When You Sell
Accelerated depreciation is a timing benefit, not a permanent one. When you sell the property, part of what you deducted gets recaptured, and knowing the trade-off before you file matters.
The 5-year and 7-year assets from your study are Section 1245 property. Gain attributable to depreciation previously claimed on these assets is taxed as ordinary income at your full marginal rate, up to 37%.11Office of the Law Revision Counsel. 26 USC 1245 – Gain From Dispositions of Certain Depreciable Property Gain above the depreciation amount is a Section 1231 gain taxed at capital gains rates.12Internal Revenue Service. Publication 544 (2025), Sales and Other Dispositions of Assets Depreciation on the 27.5-year or 39-year shell falls under Section 1250, and the unrecaptured Section 1250 gain is taxed at a maximum of 25%.13Internal Revenue Service. Topic No. 409, Capital Gains and Losses
The math still favors most owners because a dollar saved today is worth more than a dollar owed years later, particularly if you reinvest the savings. A Section 1031 like-kind exchange defers both the capital gain and the recapture by rolling into another qualifying property. If you plan to sell within two or three years of running the study, though, run the recapture numbers first. The refund you claim now can shrink meaningfully at closing.