You buy a commercial building for $1 million. The IRS says you get to write off the building portion over 39 years. That's about $15,400 per year in depreciation.
But $15,400 per year doesn't move the needle. Not when you just wrote a seven-figure check.
The tax code gives you two ways to speed that up: cost segregation and Section 179. These are different tools that solve different problems. Cost segregation reclassifies pieces of your building into shorter depreciation schedules. Section 179 lets you write off certain property in full the year you buy it. They work on different assets, follow different rules, and have different limitations.
This matters right now because the One Big Beautiful Bill Act (OBBBA), signed into law on July 4, 2025, restored permanent 100% bonus depreciation and more than doubled the Section 179 expensing limits. If you own real estate or plan to buy it, these are the two most important provisions to understand.
This guide breaks down how each strategy works, what changed under the OBBBA, where the original version of this article had errors, and how to use both tools together for maximum benefit.
What Is Cost Segregation?
When you buy a building, the IRS treats the whole thing as one asset. Residential rental property depreciates over 27.5 years. Commercial property over 39 years. That's a long time to wait for your tax deductions.
Cost segregation changes the math. An engineering-based study examines every component of your property and identifies items that qualify for shorter depreciation periods. Electrical systems, specialized plumbing, flooring, cabinetry, parking lots, landscaping, and similar items get reclassified from the 27.5 or 39-year bucket into 5, 7, or 15-year recovery periods.
On a typical property, 20% to 35% of the building basis gets reclassified into these shorter categories.
Here's where it gets powerful. Under IRC Section 168(k), property with a recovery period of 20 years or less qualifies for bonus depreciation. And thanks to the OBBBA, that bonus rate is now permanently 100% for qualifying property acquired and placed in service after January 19, 2025.
The result: reclassified components are written off in full in Year 1. A $1 million building with 30% reclassification generates $300,000 in first-year deductions instead of $15,400.
Who Should Get a Cost Segregation Study?
Properties valued above $100,000 are the typical starting point where study costs are justified by the tax savings. A study on a $750,000 property costs $2,500 to $5,000. A $750,000 building with a $600,000 basis might reclassify $180,000 to $210,000 into shorter recovery periods, generating $63,000 to $73,500 in Year 1 tax savings at a 35% rate. That's a return on investment somewhere between 1,400% and 2,700%.
Cost segregation also works retroactively. If you already own a building and never did a study, you can file Form 3115 (Change in Accounting Method) and take the catch-up depreciation in one year. No amended returns required.
What Is Section 179?
Section 179 of the Internal Revenue Code lets businesses deduct the full cost of qualifying property in the year it's placed in service, rather than depreciating it over time. Think of it as an immediate write-off for business assets.
Unlike bonus depreciation, Section 179 is an election. You choose which assets to expense and how much to deduct, up to the annual limit. You make that election on Form 4562 with a timely filed return (including extensions).
What Qualifies for Section 179?
- Tangible personal property used in a trade or business (equipment, machinery, furniture)
- Off-the-shelf software
- Qualified Improvement Property (QIP): Interior improvements to nonresidential buildings placed in service after the building was first placed in service, excluding enlargements, elevators, escalators, and internal structural framework
- Specific nonresidential building improvements: roofs, HVAC systems, fire protection and alarm systems, and security systems
- Certain business vehicles (with specific limitations based on weight)
Key Limitations
Income limitation: Section 179 deductions cannot exceed your taxable income from the active conduct of a trade or business for the year. W-2 wages count toward this limit. Unlike bonus depreciation, Section 179 cannot create a net operating loss.
Carryforward: Unused Section 179 amounts carry forward indefinitely as Section 179 expense (not as NOL) until you have sufficient business income.
Active trade or business requirement: The property must be used in an active trade or business. This is a critical distinction for rental property owners, which we'll address below.
What Changed Under the OBBBA
The OBBBA made three major changes to accelerated cost recovery. All three matter for real estate investors.
1. Permanent 100% Bonus Depreciation
Under the TCJA, 100% bonus depreciation was set to phase down: 80% in 2023, 60% in 2024, 40% in 2025, 20% in 2026, and 0% after that. The OBBBA reversed this entirely.
For property acquired and placed in service after January 19, 2025, 100% bonus depreciation is now permanent. No sunset. No phase-down.
Watch out for the gap period. Property placed in service between January 1, 2025 and January 19, 2025 falls under the old TCJA schedule at 40% bonus depreciation. The difference between placing something in service on January 18 versus January 20 can be significant.
Property acquired under a written binding contract before January 20, 2025, is not eligible for the new 100% rate, even if placed in service later. There is a transitional component election that allows taxpayers to treat individual components acquired after January 19, 2025, as eligible for 100%, even if the larger property was acquired earlier.
2. Doubled Section 179 Limits
The OBBBA more than doubled the Section 179 thresholds, effective for tax years beginning after December 31, 2024:
Both the deduction limit and phase-out threshold are indexed for inflation starting in 2026. Note that the pre-OBBBA inflation-adjusted amounts for 2025 were $1,250,000 and $3,130,000 respectively. The new statutory amounts represent a true doubling of the base figures.
3. New Section 168(n): Qualified Production Property
This is a brand-new provision that the original version of this article did not cover. The OBBBA created Section 168(n), which allows taxpayers to elect 100% first-year expensing of certain nonresidential real property used in manufacturing, agricultural production, or chemical refining.
This is significant because real property normally depreciates over 39 years and is excluded from Section 168(k) bonus depreciation. Section 168(n) extends immediate expensing to certain production buildings and structures.
Key requirements: construction must begin after January 19, 2025 and before January 1, 2029, the property must be placed in service before January 1, 2031, original use must commence with the taxpayer, and the property must be used in the United States. Property used for offices, lodging, parking, sales, or research does not qualify.
If you own manufacturing or production facilities, this provision should be on your radar. A cost segregation study becomes even more valuable in identifying which portions of a production facility qualify under Section 168(n) versus the standard bonus depreciation rules.
Section 179 and Rental Property: Getting the Rules Right
Section 179 requires that property be used in the active conduct of a trade or business under IRC Section 162. Rental property can qualify as a trade or business if you are actively involved in managing the property. This is a lower threshold than many realize. You don't need Real Estate Professional Status. You do need to be making management decisions, handling repairs (or directing them), marketing vacancies, and overseeing tenant relations. A triple-net lease where you have minimal involvement typically will not qualify.
For residential rentals that qualify as a trade or business, Section 179 is limited to tangible personal property: appliances, furniture, carpets, window treatments, and similar items placed inside the rental units.
For nonresidential (commercial) rentals that qualify as a trade or business, Section 179 extends to QIP, roofs, HVAC systems, fire protection systems, and security systems. These building improvement categories do NOT apply to residential rental property.
This is an important distinction. If you own apartments, you can Section 179 the appliances and furniture, but not the roof or HVAC. If you own an office building or retail center, those building systems are eligible.
For most residential rental property owners, bonus depreciation through a cost segregation study is the more powerful tool.
Using Both Strategies Together
Cost segregation and Section 179 are not competing strategies. They address different assets and follow different rules. The most tax-efficient approach is to use both.
The Coordination Rule
Apply Section 179 first to specific qualifying assets where you want timing control. Then bonus depreciation (identified through cost segregation) applies automatically to remaining qualified property.
This matters because Section 179 is elective and gives you control. You choose which assets, how much, and when. Bonus depreciation is automatic. Having the flexibility to allocate Section 179 strategically, then letting bonus depreciation handle the rest, gives you the best of both worlds.
Example: $1 Million Office Building (Acquired After January 19, 2025)
Assume a $1 million purchase with $200,000 allocated to land, leaving $800,000 of depreciable basis.
- Elect Section 179 on $200,000 of QIP (tenant improvements)
- Conduct cost segregation on the entire property
- Study reclassifies $240,000 of remaining basis into 5, 7, and 15-year property
- 100% bonus depreciation applies automatically to that $240,000
- Total Year 1 accelerated deductions: $440,000
- Tax savings at 35%: $154,000
- Study cost: $4,000 to $5,000
Without either strategy, your Year 1 depreciation on $800,000 of 39-year property would be about $10,250.
Income Limitations and Cash Flow
This is where the two strategies differ most.
Bonus Depreciation (via Cost Segregation)
- No income limitations. Deductions apply regardless of profit level.
- Can create or increase net operating losses.
- Works for investors with current losses from other activities.
- Predictable based on property composition.
Section 179
- Requires sufficient business income to support the deduction.
- A $500,000 deduction requires $500,000 in business income (including W-2 wages).
- Cannot create a net operating loss.
- Excess carries forward indefinitely as Section 179 expense.
- Creates uncertainty if income fluctuates year to year.
For investors who don't have consistent positive income, cost segregation with bonus depreciation is the more reliable path.
State Tax Conformity
This is the factor most people overlook, and it can change which strategy is more valuable.
Many states do not conform to federal bonus depreciation. California completely disallows it and limits Section 179 to $25,000. New York and New Jersey disallow bonus depreciation. About a dozen states have some form of nonconformity.
In those states, cost segregation with bonus depreciation creates large federal deductions that must be added back on the state return. That means higher state tax bills and more complex recordkeeping.
Section 179, on the other hand, has broader state conformity. Many states that reject bonus depreciation do conform to Section 179 limits. In those states, a Section 179 election provides both federal and state benefit while bonus depreciation only works federally.
Action item: Before implementing either strategy, check your state's conformity position. This one factor can flip the entire analysis.
Depreciation Recapture: Plan Before You Accelerate
Every dollar of accelerated depreciation creates a future tax obligation when you sell. This is not a reason to avoid acceleration, but it is a reason to plan for it.
Section 1245 Property (Personal Property and Land Improvements)
All depreciation on Section 1245 property, whether from MACRS, bonus depreciation, or Section 179, is recaptured as ordinary income at rates up to 37% when sold at a gain. This includes 5, 7, and 15-year property identified in a cost segregation study.
Section 1250 Property (Buildings and Structural Components)
Straight-line depreciation on buildings is taxed at the 25% unrecaptured Section 1250 gain rate when sold at a gain. Any bonus depreciation claimed on QIP is recaptured at ordinary income rates (up to 37%). Gain above total depreciation is long-term capital gain (15-20%).
Managing Recapture
- Hold long-term: The time value of money makes current deductions more valuable than equal future tax bills. A $200,000 deduction today is worth more than a $200,000 recapture bill in 15 years.
- 1031 Exchange: Defers recapture by rolling into replacement property. But be aware that cost segregation complicates 1031 exchanges because reclassified personal property must be exchanged for like-kind personal property.
- Step-up at death: Heirs receive a stepped-up basis, eliminating recapture entirely.
- Model the exit before you implement: Run the numbers on your expected hold period, tax rate at disposition, and time value of money before committing to aggressive acceleration.
When to Use Each Strategy
Cost Segregation Dominates When:
- You plan to hold for 5+ years
- You need to offset passive income (cost segregation deductions retain their passive character) or you are a real estate professional
- You're acquiring 1031 exchange replacement property that needs basis allocation
- You have prior-year properties that never had a study (catch-up via Form 3115)
- Your state doesn't conform to bonus depreciation but you still want federal benefit
Section 179 Works Best When:
- You're making specific equipment purchases or commercial building improvements
- You have high current-year business income and want immediate offset with timing control
- Your state conforms to Section 179 but not bonus depreciation
- You want to control exactly which assets get expensed and in what amount
- You're in an equipment-heavy business without significant real property
Use Both When:
- You own commercial property and are making improvements
- You want Section 179 timing control on specific assets plus bonus depreciation on everything else
- You're acquiring property after January 19, 2025 and want to maximize Year 1 deductions
The Bottom Line
With permanent 100% bonus depreciation and doubled Section 179 limits, the tools available to property owners in 2025 and beyond are the strongest they've been in the history of the tax code.
But tools without a plan create problems. State conformity issues, recapture exposure, income limitations, and implementation timing can all undermine an otherwise solid strategy.
The investors who get this right are the ones who model the full picture: federal and state impacts, entry and exit, current-year deductions and future recapture, and the interaction between cost segregation, Section 179, and the new Section 168(n) provisions.
If you own property or plan to buy it, start with a cost segregation benefit analysis. It's the fastest way to see what's available.
