Cost Segregation Studies: Accelerating Depreciation on Rental Property

A cost segregation study is worth its fee when the tax it saves in the years you can actually use its extra deductions clearly exceeds what you pay for it. The study splits a building's cost into parts depreciated over 5, 7, or 15 years instead of 27.5 years (39 for a commercial building), and for property acquired after January 19, 2025, those parts qualify for 100% bonus depreciation in the first year. The payoff is smaller when the passive loss rules keep you from using the loss, or when you sell soon, because gain on reclassified personal property, up to the depreciation taken, is taxed as ordinary income at sale.

What does a study reclassify?

A study allocates the purchase or construction cost among land, the building, land improvements, and personal property such as appliances. The IRS Cost Segregation Audit Technique Guide, which IRS examiners use to review studies, includes a table of common residential rental assets. Examples from it:

The guide tells examiners not to change categories or recovery periods when a return classifies residential rental assets the way this table does. Ceiling fans, built-in shelving, and attached decks also stay at 27.5 years. Reclassified property you acquired before January 20, 2025, gets the old phase-down rate instead of 100%, which is 20% if placed in service in 2026; bonus depreciation for real estate lists the rates.

Who performs a study, and what does the IRS expect?

The IRS sets no required credentials for preparers, but its guide says a study by a construction engineer is generally more reliable than one by someone without an engineering or construction background, and that cost-estimating experience and tax knowledge also matter. For a building you bought, the only cost record may be the purchase price, so the study estimates what each asset would cost to replace new, minus an allowance for its age and condition. The guide expects those estimates, plus the land's value, to reasonably match the purchase price.

The guide lists 13 elements of a quality study. Before you hire a firm, ask whether its report will:

• Name the preparer and state their credentials and experience.
• Describe the method. The guide calls a detailed engineering approach built on actual construction cost records generally the most methodical and accurate.
• Include a site visit with photographs, which the guide expects for purchased buildings as well as new construction.
• Reconcile the allocated costs to the total cost and list the personal property separately.
• Address the accounting method change if the building was placed in service in an earlier year.

Examiners are told to treat "rule of thumb" studies, which apply a fixed industry percentage with little documentation, with caution, and the guide rejects raising every estimate by the same factor just to match the purchase price. Get a written fee quote and the firm's estimate of the amounts it expects to move into each class, then run the numbers below with them.

A worked break-even example

You buy an 8-unit apartment building for $1,200,000, close in February 2026, and have it ready to rent in March 2026. The assessor's ratio puts the land at 20%, leaving a $960,000 building basis. Assume a firm quotes $8,000 and its study moves $153,600 (16% of the basis) into shorter classes: $96,000 of 5-year property and $57,600 of 15-year land improvements.

The study adds $149,178 of 2026 depreciation. To get the fee back in 2026 tax savings, you need to use extra deductions equal to the fee divided by your tax rate: $33,333 at 24%, or $25,000 at 32%. Whether you can depends on the passive loss rules:

• You can use rental losses, for example as a real estate professional who materially participates in this rental (such as by working on it more than 500 hours a year), or because other rentals give you enough passive income. The full $149,178 then counts, and at a 24% rate it cuts 2026 federal tax by about $35,800, more than four times the fee.
• You cannot use rental losses, because you have no other passive income and your modified adjusted gross income (MAGI) is $150,000 or more. Suppose the building nets $50,000 in 2026 after expenses and interest, before depreciation. Without a study, $22,362 of that is taxable. The study's extra depreciation wipes out that $22,362, saving about $5,367 at 24%, which is less than the fee. The other $126,816 becomes a suspended passive loss that carries forward until passive income absorbs it or you sell the property in a taxable sale.
• In between, the $25,000 special allowance for owners who actively participate covers part of the loss if your MAGI is under $150,000; it phases out starting at $100,000.

The extra deduction is a timing shift: you deduct the same $960,000 over the life of the property either way. With the study, building depreciation from 2027 on is $29,321 a year instead of $34,906, and a sale triggers the recapture described below.

Can you do a study on a building you already own?

Yes. A look-back study on a building placed in service in an earlier year lets you claim the depreciation you missed without amending returns. Once you have filed two returns using the original classification, the IRS treats moving assets to shorter recovery periods as a change in accounting method. You file Form 3115 under the IRS's automatic change procedures with your timely filed return for the year of change, including extensions, and send a signed copy to the IRS. The audit guide says amended returns based on a later study should generally be disallowed. The difference between the depreciation you claimed and what the study shows you were allowed is a negative section 481(a) adjustment, a catch-up deduction taken in full in the year of change.

If you did not elect out of bonus depreciation in the year you placed the building in service, the catch-up can include the bonus percentage that applied then, such as 60% for assets acquired after September 27, 2017, and placed in service in 2024. The catch-up is a rental deduction, so the passive loss rules limit it the same way. How to calculate rental depreciation walks through Form 3115 for missed depreciation.

What happens when you sell?

The study changes how part of your gain is taxed. Gain on the reclassified 5- and 7-year assets, up to the depreciation you claimed on them, is ordinary income taxed at your regular rate, which reaches 37% in 2026. Gain on land improvements is ordinary income to the extent your depreciation exceeded straight-line amounts (equal yearly deductions), which bonus depreciation does. Gain from the building's straight-line depreciation is unrecaptured section 1250 gain, taxed at no more than 25%. Keep the study with your tax records so your preparer can allocate the sale price among the assets. How depreciation recapture works covers the calculation.

For where cost segregation fits among other rental tax strategies, see tax planning strategies for rental property income.