State conformity to bonus depreciation splits roughly three ways: about 15 states fully allow the federal 100% first-year deduction under IRC Section 168(k), the largest group decouples entirely and requires an add-back, and a handful sit in between with partial conformity. That means even though the One Big Beautiful Bill Act made 100% bonus depreciation permanent at the federal level in 2025, most businesses filing across state lines still need a second depreciation calculation for state purposes.
Your state’s category determines everything that follows: whether you file one depreciation schedule or two, whether the timing of your write-off matches federally, and whether selling the asset later triggers a mismatched gain.
The Three Conformity Categories
Every state with a corporate income tax falls into one of three groups. Identifying yours is the first step.
Full Conformity
Roughly 15 states allow the same Section 168(k) first-year deduction the federal government does, and three additional states have enacted their own permanent full expensing regardless of what the IRC says.1Tax Foundation. State Tax Implications of the One Big Beautiful Bill Act In these states the federal deduction flows directly onto the state return. One calculation, no separate schedule, no timing difference to track for the life of the asset.
Full Decoupling
The largest group rejects federal bonus depreciation outright. Taxpayers add back the entire Section 168(k) deduction on the state return and instead calculate depreciation using standard MACRS applied to the full cost of the asset. Some states require straight-line depreciation rather than the accelerated MACRS rates.
The driver is revenue predictability. An immediate 100% write-off produces large swings in state collections, and states cannot run deficits the way the federal government does. Several states have automatic decoupling triggers built into their tax codes, and multiple states passed decoupling legislation in 2025 specifically in response to the OBBBA’s restoration of full bonus depreciation.2National Conference of State Legislatures. 2025 Tax Conformity Changes
Partial Conformity
A handful of states take a middle path, allowing some bonus depreciation but capping it below the federal level. Two states, for example, allow only a small percentage of the federal amount rather than the full 100%.1Tax Foundation. State Tax Implications of the One Big Beautiful Bill Act Others limit the deduction to certain asset classes or run their own phase-in schedules unrelated to the federal timeline. Partial conformity produces the most complex calculations, because you compute a partial add-back for the difference between the federal deduction and what the state actually allows, sometimes on an asset-by-asset basis.
Why Rolling Conformity Doesn’t Answer the Question
Businesses often assume that if their state uses rolling conformity, it automatically picked up the OBBBA’s permanent 100% deduction. That assumption is wrong often enough to be dangerous.
A rolling conformity state ties its tax code to the IRC as it currently reads, so federal changes flow through without new state legislation. A fixed-date or static conformity state ties its code to the IRC as of a specific date, and the legislature must update that date for federal changes to apply. As of early 2026, no static conformity state had a conformity date post-dating the OBBBA’s enactment without additional legislative action.3Council On State Taxation. State IRC Conformity Chart
Here’s the catch: many rolling conformity states have separate statutory provisions that specifically decouple from bonus depreciation regardless of what the IRC says. Rolling conformity is the default, but a targeted carve-out overrides it. So the only reliable way to know your state’s treatment is to check its actual bonus depreciation rule, not just its general conformity method.
The Add-Back and Subtraction Mechanics
In a decoupled state, the compliance task follows a two-step pattern that plays out over the life of every asset. Getting either step wrong costs money.
Year One: The Add-Back
In the year the asset is placed in service, you add back the difference between the federal deduction and what the state allows. Take a $500,000 piece of 7-year equipment. Federally you deduct the full $500,000. If your state allows only standard MACRS (roughly $71,450 in year one under the 200% declining balance method), you add back about $428,550 on your state return.
That add-back creates a gap between federal basis (now zero) and state basis (still close to original cost). The state has to let you recover that gap over time.
Later Years: The Subtraction
Each year after, you claim a subtraction modification equal to the state-allowed depreciation for that year minus any small MACRS amount already sitting in federal taxable income. The subtractions continue until state basis reaches zero. Over the full recovery period, cumulative subtractions equal the original add-back, so no revenue is permanently lost to the state. The difference is timing.
Some states use a fixed recovery mechanism instead of MACRS: they spread the add-back evenly over a set number of years, with five being common. In those states, the annual subtraction is just the total add-back divided by the recovery period.
What the Timing Difference Costs
The point of bonus depreciation is putting money back into the business now. When a state forces recovery over 5 to 20 years instead of one, you pay more state tax in year one and slowly recoup it. A business buying $2 million in equipment in a state with a 7% corporate rate and full decoupling faces roughly an additional $120,000 in state taxes in year one compared with a conforming state.
The Disposition Trap
The basis gap creates a less-obvious problem when you sell, scrap, or trade in the asset. Federal and state gain will not match, and this catches taxpayers off guard.
Suppose you bought equipment for $200,000, wrote off the full cost federally in year one, and sold it three years later for $80,000. Your federal basis is zero, so you have an $80,000 federal gain. On the state side you’ve been depreciating the asset over its MACRS life, so state basis might sit around $75,000 at sale, producing only a $5,000 state gain. The state return needs an adjustment, and any remaining subtraction modifications you would have claimed in future years are typically accelerated into the disposition year.
State rules on that acceleration vary. Some require all remaining subtractions in the year of sale; others recapture the add-back benefit under separate rules. Get this wrong and you either pay tax twice on the same income or claim a deduction the state doesn’t allow. Track state basis for every asset from acquisition through disposal, not only during the years you’re claiming subtractions.
Section 179 as the Workaround
Even in decoupled states, Section 179 expensing usually offers an alternative path to first-year write-offs. The federal Section 179 limit for 2026 is $2,560,000, with a phase-out beginning at $4,090,000 in total equipment purchases. The vast majority of income-tax states allow some form of Section 179 deduction, though many impose lower caps than the federal limit.4Tax Foundation. Consistent and Predictable Business Deductions: State Conformity With Section 179 Deductions
Section 179 and bonus depreciation overlap in what they accomplish but work differently. Section 179 is an election you make asset by asset. Bonus depreciation applies automatically to an entire property class unless you elect out of the whole class under Section 168(k)(7), and that election can be revoked only with IRS consent.5Office of the Law Revision Counsel. 26 US Code 168 – Accelerated Cost Recovery System In a decoupled state, Section 179 often provides the only practical route to immediate expensing at the state level for smaller purchases.
Some states also offer their own accelerated depreciation incentives tied to economic development goals: enhanced write-offs for manufacturing equipment, property in designated enterprise or opportunity zones, or investment tied to job creation. These operate independently from federal bonus depreciation and remain available even in fully decoupled states. Claiming them usually requires a state-specific form separate from federal Form 4562.6Internal Revenue Service. About Form 4562, Depreciation and Amortization
Multi-State Tracking and the 2025 Transition
For a business filing in one conforming state, none of this adds much work. The real burden falls on companies operating across multiple jurisdictions with different conformity positions.
Start by mapping every state where you file to one of the three categories. The Council on State Taxation publishes a conformity chart, and the Tax Foundation tracks state responses to the OBBBA. These change as legislatures update conformity dates or pass new decoupling provisions, so check annually rather than relying on last year’s map.
Build the dual-tracking system before you place assets in service, not at filing time. Reconstructing state basis after the fact is where errors creep in. For each asset, record the federal bonus amount taken, the state-allowed first-year depreciation, the add-back amount, and the expected annual subtraction schedule. Carry it forward through disposition. If two states use different conformity dates or different depreciation methods, you need a separate schedule for each state. A state that conformed to the IRC as of 2018 may produce different MACRS results than one that conformed as of 2025, because federal depreciation provisions changed during that window.
One transition detail matters for 2025 returns filed in 2026. Property placed in service between January 1 and January 19, 2025, was still subject to the old 40% bonus rate. Property acquired and placed in service after January 19, 2025, qualifies for the restored 100%.7Internal Revenue Service. Interim Guidance on Additional First Year Depreciation Deduction (Bonus) – Notice 2026-11 A business that placed assets in service on both sides of that date has two different federal depreciation treatments in the same tax year, each of which must be separately evaluated against each state’s conformity rules.