How to Apply Cost Segregation on Your Tax Return

Applying cost segregation on your tax return means moving the study’s reclassified components onto two IRS forms: Form 4562 for the ongoing accelerated depreciation each year, and Form 3115 for a one-time catch-up deduction if the property was placed in service in a prior year. The study itself is not filed with the return, but its results drive every number you report, and a 2025 law change restoring 100 percent bonus depreciation for property acquired after January 19, 2025 makes the first-year deduction substantially larger for recent purchases.¹

What You Need From the Study Before You File

The engineering study is the source document for everything on the return. Before you can fill in a single form, the report needs to give you a component-by-component inventory that reconciles to your original tax basis, with each component assigned to a specific MACRS recovery period (typically 5-year, 7-year, or 15-year) and supported by photographs, invoices, and legal citations.

The IRS’s Cost Segregation Audit Technique Guide sets out what a defensible study looks like, and examiners use it as a checklist. A study that lacks a site visit, relies on estimated percentages instead of actual construction costs, fails to reconcile segregated costs back to the original basis, or omits legal authority for each classification decision is the kind of study that collapses on audit. If any of those weaknesses exist, fix them before filing, not after a notice arrives.

Everything the study does not pull into a shorter category stays in the 27.5-year bucket (residential rental) or 39-year bucket (commercial) and continues to depreciate straight-line under the mid-month convention. So the study leaves you with two parallel depreciation schedules to track from that point forward.

Form 3115: Claiming the Catch-Up for an Existing Property

If the property was placed in service in an earlier tax year and you’re only now performing the study, the IRS treats the reclassification as a change in accounting method. You do not amend prior returns. Instead, you file Form 3115, Application for Change in Accounting Method, and take the entire catch-up in the current year.²

Automatic Consent and DCN 184

This change qualifies for automatic consent, so no user fee is required and you do not wait for IRS approval before taking the deduction. On the form, enter Designated Change Number 184, which covers changes in depreciation method, life, or convention for depreciable property.² The IRS updates its list of automatic changes through periodic revenue procedures, so confirm you are referencing the most current one when you file.

The Section 481(a) Adjustment

The Section 481(a) adjustment is the number that produces the catch-up deduction. You calculate it by taking the depreciation you should have claimed under the new, shorter lives (including any bonus depreciation that would have applied in the placed-in-service year) and subtracting the depreciation you actually claimed under the old, longer life. The difference is a negative adjustment that flows through as a single-year deduction, reported on Part IV, line 26 of Form 3115.²

For a property held several years with a meaningful share of basis reclassified into shorter-life assets, this catch-up can run into six figures.

How to File the Form

Two copies are required. Attach the original to your timely filed federal return (including extensions) for the year of the change. Send a signed duplicate copy separately to the IRS in Ogden, Utah, at Internal Revenue Service, Ogden, UT 84201, Attn: M/S 6111.³ Sending the duplicate to the wrong location can be treated as failing to file the form.

Two restrictions to check before you file. First, automatic consent is generally unavailable if you already changed the accounting method for the same asset within the preceding five tax years. Second, the change is prospective; the catch-up flows entirely through the Section 481(a) adjustment rather than through amended returns.

Form 4562: Reporting Depreciation Every Year

Form 4562, Depreciation and Amortization, is where you report both the first-year deductions and the ongoing depreciation from the study.⁴ After a study, you will run two schedules in parallel on this form: the accelerated assets from the study and the remaining structural shell.

The 5-year, 7-year, and 15-year property is reported in Part III, Section B under the General Depreciation System. The remaining building basis, still on the 27.5-year or 39-year straight-line schedule, is reported in Part III, Section C. Bonus depreciation is claimed in Part II.

Under IRC Section 168(b), 5-year and 7-year property depreciates using the 200 percent declining balance method, switching to straight-line when that produces a larger deduction; 15-year property uses 150 percent declining balance.⁵ The half-year convention is the default for the personal property from your study, but if more than 40 percent of the total depreciable basis placed in service during the year falls in the last three months, the mid-quarter convention applies instead and reduces first-year deductions for property placed in service earlier in the year.⁶

Keep a detailed depreciation schedule outside the return listing every segregated asset, its cost basis, assigned MACRS life, method, and annual deduction. It is not filed, but it is your audit defense and the basis for calculating gain or loss when you sell or dispose of components.

Where the Deduction Ends Up on Your Return

The total from Form 4562 flows to the return that matches how the property is held:

Individual rental owners report on Schedule E, Supplemental Income and Loss.
Sole proprietors report on Schedule C.
Partnerships report on Form 1065, with each partner’s share passing through on Schedule K-1.
Corporations report on Form 1120 or Form 1120-S.

The Section 481(a) catch-up from Form 3115 does not flow through Form 4562. Report it separately on the “Other Deductions” or “Other Expenses” line of the applicable return or schedule, and label it clearly as a Section 481(a) adjustment. Clear labeling helps the IRS tie the deduction back to the Form 3115 you filed and heads off correspondence.

How Much Bonus Depreciation You Can Take

Bonus depreciation is claimed in Part II of Form 4562, and the rate depends on when the property was acquired, not when you filed the study.

For property acquired and placed in service after January 19, 2025, the One Big Beautiful Bill Act permanently restored 100 percent bonus depreciation, replacing the earlier phasedown.¹ For those properties, all of the segregated 5-year, 7-year, and 15-year components can be written off entirely in the first year.

Property acquired before January 20, 2025 remains on the original phasedown schedule: 80 percent for 2023, 60 percent for 2024, 40 percent for 2025, and 20 percent for 2026.¹ If you bought a building in 2022 and are running the study now, the bonus rate that applies to each component is the one in effect when the property was placed in service. The Section 481(a) calculation on Form 3115 handles that automatically.

Whether You Can Actually Use the Loss

The deduction is only worth what you can actually claim against income, and rental real estate is passive by default under IRC Section 469. Passive losses can only offset passive income, not W-2 wages or active business income.⁷

There is a limited exception. If you actively participate in managing a rental, up to $25,000 of losses can offset non-passive income. That allowance phases out by $1 for every $2 of AGI over $100,000 and disappears completely at $150,000 AGI.⁷ For married taxpayers filing separately who lived together at any point in the year, the allowance is zero.

The full unlock is real estate professional status under IRC Section 469(c)(7). If more than 50 percent of your personal services during the year are performed in real property trades or businesses in which you materially participate, and you perform more than 750 hours in those activities, rental income and losses become non-passive and can offset any type of income.⁷ On a joint return, one spouse must meet both tests individually.

The IRS looks hard at these claims, and vague after-the-fact estimates rarely survive Tax Court. Keep contemporaneous time logs.

If you cannot use the losses this year, they aren’t lost. Suspended passive losses carry forward and can offset future passive income or be released when you dispose of the property.

What Recapture Will Cost When You Sell

Cost segregation defers tax rather than eliminating it. When you sell, part of the depreciation is recaptured, and the rate depends on the asset category.

The 5-year and 7-year assets are Section 1245 property. Gain up to the amount of depreciation claimed on those assets is taxed as ordinary income at your full marginal rate, not at capital gains rates.⁸ Recapture applies to the lesser of the gain recognized or the total depreciation previously claimed.

The structural shell and 15-year land improvements are generally Section 1250 property. Gain attributable to straight-line depreciation on real property is unrecaptured Section 1250 gain, taxed at a maximum rate of 25 percent. Gain above the depreciation amount is taxed at long-term capital gains rates.

The larger the front-end deduction from the study, the larger the potential back-end recapture. A 1031 exchange can defer it further, and holding until death may eliminate it through stepped-up basis, but plan for it either way.

State Returns May Not Follow the Federal Result

Federal bonus depreciation does not always carry through to your state return. Roughly half of states either fully decouple from federal bonus depreciation or impose their own modifications, requiring an addback when computing state taxable income. About 18 states and Washington, D.C. require a complete addback, and another 14 impose partial limitations such as per-asset caps or modified recovery periods.

The accelerated MACRS depreciation from the shorter recovery periods generally still applies at the state level even where bonus is disallowed, so the study still has value. You will need two depreciation schedules going forward: one for federal, one for state. Review the study output against your state’s conformity rules before filing.

1
Internal Revenue Service. Notice 2026-11, Interim Guidance on Additional First Year Depreciation Deduction
2
Internal Revenue Service. Instructions for Form 3115 – Application for Change in Accounting Method
3
Internal Revenue Service. Where to File Form 3115
4
Internal Revenue Service. About Form 4562, Depreciation and Amortization
5
Office of the Law Revision Counsel. 26 U.S. Code 168 – Accelerated Cost Recovery System
6
eCFR. 26 CFR 1.168(d)-1 – Half-Year and Mid-Quarter Conventions
7
Office of the Law Revision Counsel. 26 U.S. Code 469 – Passive Activity Losses and Credits Limited
8
Office of the Law Revision Counsel. 26 U.S. Code 1245 – Gain From Dispositions of Certain Depreciable Property