When the One Big Beautiful Bill Act (OBBBA) became law on 4 July 2025, it did two things at once. It made 100% bonus depreciation permanent under Section 168(k), and it raised the section 179 expensing cap from roughly $1.16 million to $2.5 million (with the phaseout threshold jumping to $4 million). For 2026, inflation adjustments push the cap to $2.56 million and the phaseout to $4.09 million.
Together, they create a real strategic choice about which tool to reach for first and how to layer them. That choice is worth understanding before your next filing.
Two Tools, One Goal, Very Different Rules
Both Section 179 and cost segregation (paired with bonus depreciation) accelerate deductions. They both let you recover the cost of qualifying property faster than standard depreciation allows. The mechanics are different, though, and those differences shape your planning.
Section 179 is an election. You choose whether to take it, and you choose the amount, up to the annual cap. Cost segregation is a study; an engineering-based analysis that reclassifies portions of a building (typically 25% to 40% of its value, according to tax advisory firm AE Tax Advisors) into shorter-lived asset categories like 5-year, 7-year and 15-year property. Those reclassified components then qualify for bonus depreciation, which applies automatically unless you elect out.
The practical differences come down to five points:
- Section 179 is capped ($2.56 million for 2026); bonus depreciation has no dollar limit
- Section 179 cannot create a net operating loss (your deduction is limited to taxable business income for the year under IRC Section 179(b)(3)(A)); bonus depreciation can
- Unused Section 179 amounts carry forward to future years; bonus depreciation takes full effect the year property is placed in service
- Section 179 is an active election on your return; bonus depreciation is the default for all qualifying property in a class
- Section 179 generally enjoys broader state-level conformity; bonus depreciation faces growing state resistance
That last point deserves its own section. But first, the sequencing.
The Coordination Rule and Why It Matters Now
Under federal tax law, Section 179 is applied first. You elect a specific dollar amount of qualifying property to expense. Then bonus depreciation kicks in automatically on remaining qualifying basis. This ordering is confirmed in the IRS Form 4562 instructions and was further clarified when the IRS issued Notice 2026-11 in January 2026, providing interim guidance on how the restored 100% bonus depreciation rules work.
Most property owners think of Section 179 and cost segregation as competing options. In practice, they’re sequential. You can use Section 179 to carve out a precise deduction you control (up to your taxable income for the year, no further), and then let cost segregation with bonus depreciation handle the rest.
Say you have a profitable year and want to reduce taxable income to a specific figure without generating a loss. Section 179 lets you dial the deduction exactly to your income floor. Bonus depreciation then applies to everything else that qualifies, and it can push you into a loss if the numbers are large enough. For property owners with high-income years, that loss might be exactly the point.
The OBBBA also introduced a one-time election allowing taxpayers to claim 40% bonus depreciation instead of 100% for the first tax year ending after 19 January 2025. Combined with a carefully chosen Section 179 amount, that gives you three layers of control over how much depreciation you take and when.
On a $2 million commercial property, a cost segregation study might accelerate $400,000 to $600,000 in deductions, producing tax savings of $100,000 to $200,000 or more, according to Veritax Advisors. Studies typically cost $5,000 to $20,000, and the return on that investment is hard to argue with when reclassified components qualify for 100% first-year bonus depreciation.
The State-Level Wrinkle You Can’t Ignore
Federally, the coordination between Section 179 and bonus depreciation is clean enough. At the state level, the picture shifts.
Since the OBBBA’s enactment, several states have moved to decouple from federal bonus depreciation. Rhode Island acted first. California moved its IRC conformity date to specifically exclude OBBBA provisions. Delaware convened a special legislative session. Michigan, Pennsylvania, Illinois and the District of Columbia have all passed decoupling legislation, according to Grant Thornton and Thomson Reuters. States like Georgia, Maryland and South Carolina remain undecided.
Section 179, by contrast, enjoys broader state conformity. While some states cap the deduction at lower amounts, most recognize it. That creates a meaningful planning gap: in a state that disallows bonus depreciation, the deductions you unlocked through a cost segregation study may reduce your federal bill but do nothing for your state return.
If you file in one of those states, could Section 179 actually deliver more reliable after-tax value at the state level, even when the federal arithmetic favors cost segregation? Multi-state property owners face this calculation on every asset.
Your Move, With Your CPA
The OBBBA turned the relationship between these two tools into a genuine planning conversation. Section 179 offers a controlled, elective deduction with a clear ceiling. Cost segregation paired with bonus depreciation offers an uncapped, automatic write-off that can generate losses. The two work in sequence, and the strongest strategies tend to use both.
With IRS Notice 2026-11 providing clear guidance on how these provisions interact, and states still adjusting their positions heading into the 2026 filing season, this is a conversation to have with a qualified CPA who understands your properties, your income and your state filing obligations. Every tax situation is different, and the right combination depends on facts that are yours alone. Do your own research, ask pointed questions and make sure the strategy fits your numbers.
The tools are more generous than they’ve been in years. Is your depreciation strategy keeping pace?
