Cost segregation: taking your building apart, on paper, piece by depreciable piece

By Tom, CPA · Updated October 25, 2026

TL;DR: A cost segregation study splits a building's cost into components: personal property and land improvements that depreciate over 5, 7 or 15 years instead of 27.5 or 39. Combined with bonus depreciation, which is 100% for qualifying property acquired after January 19, 2025 (as of Oct 2026), it can create large first-year deductions. But passive loss rules may block them, the study costs money, and depreciation is recaptured when you sell.

Educational only, not tax, legal, or investment advice. Examples are illustrations, not predictions. Rules and limits change; verify current figures and talk to a qualified professional about your situation.

Normally a residential rental building is depreciated over 27.5 years: one slow, steady deduction every year until roughly the heat death of the universe, or at least your grandchildren. Cost segregation asks a sneaky question: is all of that building really "building"? What about the carpet, the appliances, the fence, the driveway and the landscaping?

Lavish Larry heard cost segregation creates "free money." Frugal Fran heard it creates earlier deductions, which is different. Start with the basics in real estate depreciation and rentals for FIRE.

CPA Warning Label: Cost segregation is a technical engineering and tax exercise. Deductions you can't use because of passive loss rules just carry forward, and accelerated depreciation increases tax when you sell. Get a qualified study and tax advice before relying on the numbers.

What a study does

Under the IRS depreciation system (MACRS), residential rental buildings use a 27.5-year recovery period, and nonresidential real property generally uses 39 years. Other property placed in a rental has shorter lives. IRS Publication 527 lists, for example, appliances, carpeting and furniture used in residential rental activities as 5-year property, and land improvements such as fences, roads and shrubbery as 15-year property. Publication 946 covers the full classification rules.

A cost segregation study, usually performed by engineers or specialized firms, examines the property and allocates the purchase price (or construction cost) among:

Moving even 20–30% of a building's basis into shorter-lived categories speeds up depreciation dramatically, especially with bonus depreciation. Total depreciation over the property's life doesn't change. Only the timing does.

Quality matters. A study should document its methodology, tie allocations to actual costs or reasonable engineering estimates, and hold up on audit. A "study" that consists of a spreadsheet and optimism can turn a tax benefit into an expensive adjustment.

Bonus depreciation rate status

Bonus depreciation lets you deduct a percentage of qualifying property's cost (generally property with a recovery period of 20 years or less) in the first year, instead of depreciating it over time. It doesn't apply to the 27.5- or 39-year building itself.

As of Oct 2026: the 2025 tax law commonly called the One Big Beautiful Bill restored 100% bonus depreciation for qualifying property acquired after January 19, 2025. IRS guidance (IR-2026-06 / Notice 2026-11) addresses how it applies, including binding-contract rules for property contracted for before that date. Property acquired earlier may be subject to the lower phase-down percentages that applied under prior law.

What it means in practice: the 5-, 7- and 15-year components identified by a study may be fully deductible in the year the property is placed in service, if acquired after January 19, 2025 and otherwise qualifying. Taxpayers can also elect out of bonus depreciation by class, which can make sense if the deductions would be wasted.

Tax laws change. Check the current rules and IRS guidance for the year you place property in service, and confirm the acquisition date rules for any property you contracted to buy before January 20, 2025.

Recapture

The catch with speeding up depreciation is that it reduces your basis faster, and when you sell, the IRS wants some of that back:

• Personal property (Section 1245) components: gain attributable to depreciation is generally recaptured as ordinary income (IRS Publication 544), taxed at your regular rates, not capital gains rates.
• Building (Section 1250) components: depreciation is generally taxed as "unrecaptured Section 1250 gain" at a maximum rate of 25% (IRS Topic 409).
• Any remaining gain is taxed at long-term capital gains rates if held more than a year.

So cost segregation can convert some future gain from 25%-max or capital gains rates into ordinary income at sale. Whether you still come out ahead depends on the time value of money, your tax rates now versus at sale, and how you exit. A 1031 exchange can defer recapture, and holding until death may result in a basis step-up for heirs under current law. Selling within a few years can mean much of the benefit gets paid back.

Who it fits

Accelerated depreciation only helps if you can actually use the deductions. Rental losses are generally passive, and under the passive activity loss rules (IRS Publication 925), passive losses can generally only offset passive income, with exceptions:

• Real estate professionals who materially participate can treat rental losses as non-passive.
• Short-term rentals with an average guest stay of 7 days or less aren't treated as rental activities for these rules. With material participation, losses may offset other income. See the short-term rental loophole.
• The $25,000 special allowance for active participants phases out between $100,000 and $150,000 of modified AGI.

Otherwise, unused losses carry forward until you have passive income or sell the property. Details are in passive activity loss rules.

Early retirees have a specific wrinkle: a giant deduction in a year when your income is already low may waste the 0% and 10–12% brackets that you could have used for Roth conversions or gain harvesting. Sometimes slower depreciation is more valuable. Straight-line deductions spread over decades can quietly shelter rental income every year of a long retirement, which may be worth more than one giant deduction you can't fully use.

Example

Illustration: Fran buys a $900,000 short-term rental in March 2026 (land $150,000, depreciable basis $750,000). A study allocates $150,000 to 5-year personal property and $60,000 to 15-year land improvements, leaving $540,000 as building.

• Without a study: first-year depreciation on $750,000 under the 27.5-year table for a March placement is about $750,000 × 2.879% ≈ $21,600.
• With a study and 100% bonus on the $210,000 of 5- and 15-year property: $210,000 bonus plus about $540,000 × 2.879% ≈ $15,500 of building depreciation, roughly $225,500 in year one.

If Fran qualifies under the short-term rental rules and materially participates, those losses might offset other income. If she doesn't, they're passive and carry forward. When she sells, the $210,000 she deducted on 5- and 15-year property may come back as ordinary income to the extent of gain on those components, which is a reason to plan exit strategy before ordering the study.

Larry orders a study on his $250,000 condo, pays the fee, can't use the passive losses, and sells two years later. He has successfully paid someone to rearrange the timing of his taxes against himself. Fran's version: run the numbers with a tax pro first. Compare with house hacking, REITs vs rentals, or just low-cost index funds.