At a glance
- They are not alternatives. A cost segregation study sorts a building into asset classes. Bonus depreciation is the rule that lets you deduct the short-lived classes at once. One finds the deduction, the other takes it.
- Bonus is back at 100% and it is permanent. For qualified property acquired after January 19, 2025, the phase-down is gone (IRS Notice 2026-11, section 2.02(1)).
- The building itself never qualifies. Bonus applies to property with a recovery period of 20 years or less, which is exactly what a study carves out of the 27.5- or 39-year shell.
- Finding the deduction and using it are separate questions. The passive loss rules and the excess business loss cap decide how much of it lands on this year’s return.
The question is usually asked as a choice: cost segregation or bonus depreciation. It is not a choice. They are two different things that happen to arrive in the same sentence at a closing dinner. A cost segregation study is an engineering analysis of what you bought: it takes a building recorded as one 27.5-year asset and breaks it into the components the tax law actually recognises, some of which have five- or fifteen-year lives. Bonus depreciation is a provision of section 168(k) that lets you deduct the entire cost of qualifying property in the year it is placed in service.
Neither does much without the other. Bonus depreciation on a residential building alone gives you nothing, because a 27.5-year asset is not qualified property. A study without bonus depreciation still helps, because five-year property depreciates faster than twenty-seven-and-a-half-year property, but it spreads the benefit over years rather than dropping it into one. Run together, they are the reason a $1.2 million purchase can produce a six-figure deduction in its first year.
What this looks like on an actual return
If you read nothing else, read this. Same building, same year, same money spent.
A residential rental bought for $1,200,000 and placed in service in January 2026. Land is $250,000, so the depreciable basis is $950,000. The study reclassifies 12% of that basis to five-year personal property and 8% to fifteen-year land improvements, a conservative result for a residential property.
| First year on the return | No study | With a study |
|---|---|---|
| Purchase price | $1,200,000 | $1,200,000 |
| Less land | ($250,000) | ($250,000) |
| Depreciable basis | $950,000 | $950,000 |
| Reclassified to 5-year personal property | — | $114,000 |
| Reclassified to 15-year land improvements | — | $76,000 |
| Left in the 27.5-year building | $950,000 | $760,000 |
| Bonus depreciation at 100% | $0 | $190,000 |
| Straight-line on the building | $33,100 | $26,500 |
| First-year depreciation deduction | $33,100 | $216,500 |
$183,400 more deducted on identical facts. At a 35% marginal rate that is roughly $64,000 of tax deferred into later years. Deferred, not forgiven. The section on selling below takes that distinction seriously.
The one-line version. The study does not create a deduction. It moves part of the building into classes that bonus depreciation is allowed to take all at once. Figures are illustrative and rounded, and assume a January placement in service under the mid-month convention.
What changed, and why the answer is different from two years ago
Bonus depreciation was on a scheduled phase-down: 80% in 2023, 60% in 2024, 40% in 2025, and zero by 2027. Every cost segregation conversation for three years carried an implicit deadline. That is over. Section 70301 of the 2025 reconciliation act replaced the phase-down with a permanent 100% deduction for qualified property acquired after January 19, 2025, and the IRS confirmed it in interim guidance:
“OBBBA § 70301 amended § 168(k) to replace the annual phasedown of the applicable percentage … with a permanent 100 percent additional first year depreciation deduction for qualified property acquired … after January 19, 2025.” Notice 2026-11, section 2.02(1)
Two practical consequences. First, the urgency is gone: a study done next year is worth what a study done this year is worth, so the decision can be made on the property rather than on the calendar. Second, there is an election to take 40% instead of 100%, or 60% for certain longer-production-period property and aircraft, for property placed in service during the first taxable year ending after January 19, 2025. That election exists for taxpayers who would rather have the deductions in later years at higher rates, and it is a real decision for someone whose income is about to rise.
What the study actually finds
A building bought as one asset contains a great deal that is not, for tax purposes, a building. The study separates it:
| Class | Typical contents | Life | Bonus eligible |
|---|---|---|---|
| Personal property | Appliances, carpet, cabinetry, decorative lighting, dedicated electrical for equipment | 5 years | Yes |
| Land improvements | Paving, sidewalks, fencing, site drainage, landscaping, exterior lighting | 15 years | Yes |
| The building | Structure, roof, plumbing, HVAC, the rest of the electrical | 27.5 or 39 years | No |
| Land | Land | Not depreciated | No |
The percentages vary more than the marketing suggests. A plain residential rental often lands between 10% and 25% of basis in the short-lived classes. A restaurant, a medical office or a short-term rental furnished to hotel standard can run far higher, because the fit-out is most of what was bought. Anyone quoting a figure before seeing the property is quoting an average, not your building.
One point that is regularly missed: used property qualifies. Section 168(k) requires only that the property was not previously used by you and was not acquired from a related party. Buying an existing apartment building is the ordinary case for a cost segregation study, not an exception to it.
Finding the deduction is not the same as using it
This is where most of the disappointment lives, and it has nothing to do with either the study or bonus depreciation. A large first-year deduction on a rental usually creates a loss, and two separate rules decide whether that loss reaches your other income.
Section 469 comes first. Rental activity is passive by default, and a passive loss offsets passive income only. The rest suspends and waits for a future year or for the sale. Three routes out: qualifying as a real estate professional and materially participating; the short-term rental position, where an average period of customer use of seven days or less means the activity is not a rental activity at all under the regulations and material participation is the only test that matters; or the $25,000 allowance for active participation, which phases out between $100,000 and $150,000 of modified AGI and is therefore irrelevant to most people asking this question.
Then section 461(l). Even a fully non-passive loss is capped. For 2026 the excess business loss threshold is $256,000, or $512,000 on a joint return (Rev. Proc. 2025-32, section 4.31). Anything above that does not vanish. It carries forward as a net operating loss. But it does not shelter this year’s wages either. On the numbers in the table above, a single filer with a $216,500 deduction stays under the cap. Two properties, and they do not.
The order matters and it is not negotiable. Section 469 is applied before section 461(l). A suspended passive loss never reaches the excess business loss calculation at all, which is why “am I passive?” is the first question and “how big is the deduction?” is the second.
A property you already own
A study is not limited to the year of purchase. For a property placed in service in an earlier year and depreciated as a single asset, the correction is a change in method of accounting on Form 3115, The entire catch-up, meaning every dollar of depreciation you could have taken and did not, is deducted in the year of change as a section 481(a) adjustment. No amended returns.
The automatic consent procedure for an impermissible-to-permissible depreciation change is section 6.01 of Rev. Proc. 2025-23, and it carries a condition worth knowing before you plan around it: the property must generally have been depreciated under the impermissible method for at least the two taxable years before the year of change. A building placed in service last year does not qualify for the automatic change on that basis, though there is a narrow exception for property placed in service in the immediately preceding year.
Whether the catch-up is usable is still the section 469 and section 461(l) question above. A $300,000 section 481(a) adjustment that suspends as a passive loss has bought you a filing, not a refund.
The bill arrives at sale
Accelerated depreciation is a timing benefit, and the timing runs out when you sell. Three different rules apply to the three pieces the study created:
| What you deducted | How it comes back | Rate |
|---|---|---|
| Five-year personal property (section 1245) | Ordinary income to the extent of depreciation allowed | Ordinary rates |
| Land improvements, to the extent bonus exceeded straight line | Ordinary income as additional depreciation under section 1250(b)(1) | Ordinary rates |
| Straight-line depreciation on the building | Unrecaptured section 1250 gain | Up to 25% |
The second row is the one that surprises people. Bonus depreciation on fifteen-year land improvements is depreciation in excess of straight line, and section 1250(b)(1) defines exactly that as additional depreciation, recaptured at 100% as ordinary income. A study that front-loads deductions at ordinary rates and returns them at ordinary rates has still won on time value, but it has not converted ordinary income into capital gain, and anyone selling it to you that way is wrong. The full mechanics are in our guide to depreciation recapture on a rental sale.
The exception is not selling. Hold to death and the basis step-up under section 1014 erases the recapture entirely; exchange under section 1031 and it is deferred into the replacement property. A study makes the hold-or-exchange decision more consequential, not less.
What to do about it
- Get the study priced before the return, not after. Fees generally run a few thousand dollars for a residential property and more for commercial. On a $950,000 basis the arithmetic is not close; on a $250,000 condo it often is.
- Answer the passive question first. If the loss suspends, the study is still correct. It is just not this year’s money. That changes when you would pay for it.
- Model the excess business loss cap with everything else on the return. The $256,000 threshold is tested against all business income and loss, not this property alone.
- Consider the 40% election deliberately if your rates are heading up. It is available for property placed in service in the first taxable year ending after January 19, 2025, and it is not the default.
- Use a study with an engineering basis. A spreadsheet allocation with no site work behind it is the kind of position that does not survive examination, and the preparer signing the return is the one holding it.
Frequently asked questions
Is cost segregation the same as bonus depreciation?
No. A cost segregation study is an engineering analysis that reclassifies parts of a building into five- and fifteen-year asset classes. Bonus depreciation is the section 168(k) rule that allows property with a recovery period of twenty years or less to be deducted in full in its first year. The study identifies what qualifies; bonus depreciation is what takes it. Neither is a substitute for the other.
Can you take bonus depreciation without a cost segregation study?
Yes, on anything already recorded as short-lived property: appliances, furniture, equipment bought separately. What you cannot do is apply it to a building recorded as a single 27.5- or 39-year asset, because that asset’s recovery period is too long to qualify. Without a study, the deduction is limited to what your fixed asset schedule already separates out.
Does bonus depreciation still phase down?
No. The phase-down to 80%, 60% and 40% was repealed for qualified property acquired after January 19, 2025, and replaced with a permanent 100% deduction. There is an election to take 40%, or 60% for certain longer-production-period property and aircraft, for property placed in service in the first taxable year ending after that date, but it is an election, not a schedule.
Can I do a cost segregation study on a property I already own?
Yes. The correction is filed on Form 3115 as an automatic change in method of accounting under section 6.01 of Rev. Proc. 2025-23, and the entire missed depreciation is deducted in the year of change as a section 481(a) adjustment rather than through amended returns. The property must generally have been depreciated under the old method for the two taxable years preceding the change, with a narrow exception for property placed in service in the immediately preceding year.
Will a cost segregation study create a loss I can use against my salary?
Only if the rental is not passive to you. Rental activity is passive by default under section 469, and a passive loss offsets passive income only. The routes out are real estate professional status with material participation, the short-term rental position where the average period of customer use is seven days or less, or the $25,000 active participation allowance, which phases out between $100,000 and $150,000 of modified AGI. If the loss is non-passive, it is then capped by the section 461(l) excess business loss threshold of $256,000, or $512,000 on a joint return, for 2026.
Related reading
- Depreciation recapture on the sale of rental property in 2026
- How to qualify for real estate professional status
- The excess business loss limitation in 2026
- Repairs versus improvements on a rental
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A short conversation about your situation, our read on it, and whether it is a mutual fit.
Sources: IRS Notice 2026-11, interim guidance on the additional first year depreciation deduction as amended by section 70301 · Rev. Proc. 2025-32, sections 4.24 and 4.31 · Rev. Proc. 2025-23, section 6.01 · 26 U.S.C. § 168(k) · 26 U.S.C. § 1250(b)(1) · 26 U.S.C. § 469. Figures in the worked example are illustrative. This is general information, not advice on your return.
