Business and individual taxpayers who acquire nonresidential real property or residential rental property have an opportunity most never take. They can stop depreciating the entire building over 39 years and start depreciating large parts of it over 5, 7 and 15. That is what a cost segregation study does. An engineer walks the property and identifies the components that are not really "building" — the dedicated electrical serving equipment, the specialty plumbing, the floor coverings, the cabinetry, the parking lot, the site lighting. Each has its own recovery period under MACRS. Left alone, all of it sits in the 39-year bucket, or 27.5 years for residential rental.
Here is what that is worth. Assume a nonresidential building acquired and placed in service this year at $2,000,000, excluding land — the acquisition date matters, because it is what decides which bonus depreciation rules apply. These figures are illustrative — your building, your numbers, and your tax position will all differ. Without a study, the whole $2,000,000 depreciates over 39 years: roughly $51,000 in year one. Now assume a study reclassifies $300,000 to 5-year personal property and $200,000 to 15-year land improvements, leaving $1,500,000 as 39-year real property. The 5-year property is eligible for the 100% first-year depreciation allowance, which the One Big Beautiful Bill Act made permanent for property acquired after 19 January 2025. The land improvements move to a 15-year life. Year one now looks like this: $300,000 for the 5-year property, about $10,000 on the land improvements, and $38,000 on what remains in the 39-year bucket. Roughly $348,000 against roughly $51,000. Call it $297,000 of additional first-year deduction — about $110,000 of tax, at the top rate, that you do not pay this year.
Most land improvements carry a 15-year recovery period. Common examples: parking lots, paving, sidewalks, curbs, fencing, outdoor lighting, drainage systems, and water and sewage lines. Inside the building a study looks for storm sewers, landscaping, signage, security and fire protection systems, removable partitions, removable carpeting and wall tiling, furniture, counters, appliances, and machinery — including machinery foundations — unrelated to the operation and maintenance of the building. It also captures the portion of electrical wiring and plumbing properly allocable to equipment rather than to the structure itself.
Read that last sentence carefully. It says the tax is not paid this year. It does not say it is saved. Over the full life of the building you depreciate $2,000,000 either way. A cost segregation study does not create deductions — it moves them forward. What you are buying is the time value of that money and the ability to use the deduction in a year when it is worth something to you. Anyone selling you a study on the promise of "savings" without using the word "timing" is selling you something other than the truth. A taxpayer engages a specialist to conduct the study. Ideally it happens before the building is placed in service — during construction or at purchase — but a study can be completed afterwards, and often is.
If you already own the building, you do not have to amend old returns. Changing the depreciation lives is an accounting method change, filed on Form 3115, and the understated depreciation from every prior year comes through as a single catch-up adjustment on one current-year return. The reporting to the IRS includes the change of basis, the depreciable lives, and the adjustment for the impact of the acceleration from the date placed in service to the year of the method change. Two things then decide whether any of this is worth doing. First, can you actually use the loss? A large first-year deduction that gets suspended is worth far less than the headline. If the rental activity is passive to you, the loss is limited under Section 469 and carries forward until you have passive income or dispose of the property. Real estate professional status is the main exception, and it is a real test — more than half your personal services in real property trades or businesses, and more than 750 hours. Meeting it does not by itself make rental losses non-passive; material participation in each rental activity is still required, or a grouping election. Second, what happens when you sell? Accelerated depreciation does not disappear at closing. It comes back as recapture, and the treatment is not the same for every asset class a study creates. Model that before you commission the study, not after — particularly if the hold period is short.
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There are also cases where a study should not be done at all: the property is small enough that the study costs more than the timing benefit is worth, the hold period is too short for that benefit to outgrow the recapture, or the owner has no way to use the accelerated deduction in the years it lands. Even where a full engineering study is impractical, it is worth asking whether there are obvious land improvements and personal property components that can be separately depreciated over a shorter recovery period. Tell us what you bought, when it went into service, and what you plan to do with it. We will tell you whether a study is worth commissioning before you spend anything on one — and if it is, we handle the depreciation, the Form 3115 and the reporting.
This post is general information about federal and state tax rules, not advice about your situation. Rules change. Check the date above before you rely on anything here, and talk to us about your own facts.