Cost segregation, in the order your CPA will ask about it

What a cost segregation study is, in one paragraph

A cost segregation study takes a building you bought as one line item and separates it into components with different tax lives. The IRS describes section 1250 property as "generally non-residential real property (with a 39-year recovery period) or residential rental property (with a 27.5-year recovery period)."¹ A study moves carpet, cabinetry, appliances, specialty electrical, paving, fencing and landscaping out of that 27.5-year bucket and into five, seven and fifteen year classes.² It creates no new deduction. It changes when you take the one you already had.

That last sentence is the whole thing, and it is the sentence most decks omit. Everything below follows from it.

Land never depreciates, at any purchase price, in any structure.³ On a deal where land is a large share of basis, a study has less to work with before it starts. That share is not a detail of the individual deal so much as a property of the asset class: a manufactured housing community or an RV park is mostly land and 15-year site work, while a self-storage facility is mostly 39-year building. Our comparison of alternative asset classes sets those recovery lives side by side.

The number that changed in 2025, and the date that governs it

Bonus depreciation decides how fast the reclassified property can be written off, and the rule changed materially. Most material still in circulation describes the old phase-down.

Treasury and the IRS state the current position directly. Section 70301 of the 2025 legislation "made several amendments to § 168(k) to provide taxpayers with a permanent 100 percent additional first year depreciation deduction for qualified property acquired and placed in service ... after January 19, 2025," replacing "the annual phasedown of the applicable percentage."⁴ For property still under the old regime, the same notice records the prior rate as "40 percent for qualified property placed in service during 2025."⁴

The third row is the trap. The statute provides that "property is not treated as acquired after the date a written binding contract is entered into for such acquisition."⁴ A property under contract on or before 19 January 2025 is treated as acquired then, even if it closed months later, and it takes 40 percent rather than 100.

Ask the sponsor one question: on what date was the written binding contract entered into, and what applicable percentage does the projection assume? A sponsor who has run the analysis answers immediately.

It is a deferral, and the bill arrives at sale

Accelerating depreciation does not increase the total deduction over the life of the asset. It moves it forward. The benefit is the time value of a deduction taken in year one instead of spread across 27.5 years, which is real, and it is a financing benefit rather than a reduction in lifetime tax.

Two mechanisms take it back. Depreciation reduces basis, so gain at sale is correspondingly larger. And the section 1245 property a study creates is recaptured as ordinary income to the extent of depreciation taken, rather than at capital gain rates. Reclassification therefore converts part of your eventual gain from capital to ordinary.

A deal can show an attractive first-year loss and a heavier than expected exit-year tax bill. Neither is a surprise if both are modeled. Investors are routinely shown the first and rarely shown the second.

Whether the trade is worth making depends on your marginal rate now against your expected rate at exit, your holding period, and what else is on your return. Those are facts about you. Any sponsor answering that question without seeing your return is selling, not advising.

The filing nobody mentions until it is late

A study performed after the acquisition year is not a recalculation. The IRS is explicit: "a change in depreciation method, recovery period or convention ... constitutes a change in accounting method. Therefore, the use of a cost segregation study to reclassify property and/or reallocate costs requires the consent of the Commissioner."¹

In practice that consent comes through an application for change in accounting method on Form 3115,⁵ which for most cost segregation changes falls under an automatic consent procedure. It is a filing rather than a discretionary approval. It still has to be prepared correctly and filed on time, and it has a cost.

The distinction that matters to you is between a study done in the acquisition year, adopted on the first return, and a look-back study on a property held for several years, which requires the method change and produces a catch-up adjustment. Both are legitimate. They are different pieces of work with different costs, and a sponsor should be able to say which is contemplated and who pays for it.

What a defensible study contains, in the examiner's own words

The IRS publishes the checklist an examiner works from, which means you can hold a sponsor to the same standard. The guide names thirteen principal elements of a quality study, including "Preparation by an Individual with Expertise and Experience," "Explanation of the Legal Analysis," "Reconciliation of Total Allocated Costs to Total Actual Costs," and "Identification and Listing of § 1245 Property."¹

On who should do the work, the guide is blunter than any sponsor will be, and the sentence deserves reading twice: "The preparation of cost segregation studies requires knowledge of both the construction process and the tax law involving property classifications for depreciation purposes. Unfortunately, there are no prescribed qualifications for cost segregation preparers."¹

It goes further: "In general, a study by a construction engineer is more reliable than one conducted by someone with no engineering or construction background," while noting that cost estimating experience and knowledge of the tax law matter too.¹ And it sets a test you can apply in thirty seconds: "a quality study identifies the preparer and always references their credentials, experience, and expertise in the cost segregation area."¹

So ask who prepared it, what their background is, and whether the report names them. A study that will not identify its own preparer has failed a standard the IRS wrote down.

Why the deduction may never reach you

This is where most investors are disappointed, and it has nothing to do with whether the study was good. Rental activity is generally passive, and passive losses offset passive income rather than wages, business income or portfolio income.⁶ The computation runs on Form 8582.⁷

With no passive income, a large first-year loss is generally suspended. It is not wasted and it does not vanish. It carries forward. But it does not reduce this year's tax on your salary, which is what a projected first-year loss is usually taken to mean.

The exception rarely helps the investors this is written for. The special allowance permits up to $25,000 of rental real estate loss against other income where you actively participated, but it "is reduced by 50% of the amount of your modified adjusted gross income that is more than $100,000,"⁶ which exhausts it entirely at $150,000. An accredited investor is generally above that line by definition.

The other route is real estate professional status, which requires both that "more than half of the personal services you performed in all trades or businesses during the tax year were performed in real property trades or businesses in which you materially participated" and "more than 750 hours of services during the tax year."⁶ A passive limited partner does not qualify through the syndication. A spouse with a qualifying career changes the analysis entirely, and that is a conversation for your CPA.

What happens when the deal sells

Suspended losses are released on a fully taxable disposition of your entire interest in the activity, becoming deductible in that year.⁶ A suspended loss is therefore a deferral rather than a forfeiture.

That gives the arithmetic a shape worth understanding before you invest. In a typical passive position the accelerated deduction is suspended in year one, carries forward, and is released in the exit year against the gain that the same accelerated depreciation helped create. The two events are connected. Looking at either alone gives a misleading picture.

The word doing the work is "entire." Partial dispositions, gifts and transfers at death follow different rules, and a disposition to a related party may not release the losses. If your position may move for estate planning reasons before the deal exits, raise it with your advisers early rather than at the point of transfer.

Your share of all of this arrives on a Schedule K-1,⁸ and the partnership reports its depreciation on Form 4562.⁹

The order your CPA will ask about it

Accountants work through this in a consistent sequence, and knowing the sequence lets you gather the answers before the call rather than after it.

First, the acquisition date and the binding contract date, because that decides the bonus percentage. Second, whether the study is acquisition-year or look-back, because that decides whether a Form 3115 is needed. Third, the preparer and their credentials, because that decides how defensible the allocation is. Fourth, your own passive income position, because that decides whether any of it reaches you this year. Fifth, the exit assumptions, because that decides what comes back.

Nothing in that list requires you to understand depreciation mechanics. It requires five facts, four of which the sponsor holds and one of which your CPA holds.

What to ask about a study

1. On what date was the written binding contract for this property entered into?
2. What applicable percentage of bonus depreciation does the projection assume, 100 or 40?
3. Is this an acquisition-year study or a look-back study requiring a Form 3115?
4. Who prepared the study, what is their construction and tax background, and does the report name them?
5. What proportion of basis was reclassified into 5, 7 and 15 year property, and what reconciles to total actual cost?
6. Who pays for the study, and is that cost inside the deal or charged to investors?
7. What does the model assume about depreciation recapture in the exit year?

What this is built on

1. Internal Revenue Service, Publication 5653, Cost Segregation Audit Techniques Guide
2. Internal Revenue Service, Publication 946, How To Depreciate Property
3. Internal Revenue Service, Publication 946, Appendix B, table of class lives and recovery periods
4. Internal Revenue Service, Notice 2026-11, interim guidance on the additional first year depreciation deduction under section 168(k)
5. Internal Revenue Service, About Form 3115, Application for Change in Accounting Method
6. Internal Revenue Service, Publication 925, Passive Activity and At-Risk Rules
7. Internal Revenue Service, About Form 8582, Passive Activity Loss Limitations
8. Internal Revenue Service, Schedule K-1 (Form 1065), Partner's Share of Income, Deductions, Credits
9. Internal Revenue Service, About Form 4562, Depreciation and Amortization