Massachusetts small business owners who filed their 2025 tax returns assuming the state would follow the federal government's big new tax breaks are in for an unpleasant surprise. In its June 2026 supplemental budget bill, Massachusetts explicitly rejected several of the most valuable federal tax provisions from the One Big Beautiful Bill Act (OBBBA) — including immediate R&D expensing and enhanced Section 179 deductions — and gave affected taxpayers until September 10, 2026 to fix returns that got it wrong.
If you run a business with any research spending, recent equipment purchases, or meaningful interest expense, this is worth twenty minutes of your attention right now, not in December when your accountant is scrambling.
What "Decoupling" Actually Means
Every year, Congress changes federal tax law, and states have to decide whether to follow along. Some states automatically adopt whatever the Internal Revenue Code says ("rolling conformity"). Massachusetts is not one of them — it uses a fixed reference date, effectively pinning its tax code to a frozen snapshot of federal law and only moving that date forward when the legislature explicitly says so.
That matters enormously this year because OBBBA (the sweeping 2025 federal tax law) rewrote several rules that businesses rely on every day. When Massachusetts "decouples" from a provision, it means: your federal return and your Massachusetts return no longer agree, and you have to make manual adjustments to your state taxable income to back out the federal benefit.
In plain terms — a deduction the IRS lets you take in full this year might have to be spread out over five years on your Massachusetts return instead. That's not a rounding error; for a business with real research spending or equipment purchases, it can mean tens of thousands of dollars in state tax due that a business owner didn't budget for.
The Four Provisions Massachusetts Rejected
1. Research & Experimental (R&D) Expensing
This is the big one. Under OBBBA, federal law now lets businesses immediately deduct domestic research and experimental (R&E) costs in the year incurred — a major reversal of the punishing five-year amortization rule that had been in effect since 2022.
Massachusetts said no. For tax years 2022 through 2025, Massachusetts still requires businesses to capitalize and amortize domestic R&E costs over five years, exactly as pre-OBBBA law required. Two details make this especially painful:
- Businesses cannot claim the federal "super deduction" — the one-time catch-up deduction for R&E costs capitalized in earlier years — on their Massachusetts return.
- Businesses cannot go back and amend 2022–2024 Massachusetts returns to claim deductions that were denied under the old five-year rule, even though the federal government effectively undid that rule.
If your business does any software development, product engineering, or formulation work that counts as R&E for tax purposes, this is the provision most likely to create a real gap between what your CPA modeled off your federal return and what Massachusetts actually owes.
2. Bonus Depreciation on Qualified Production Property
OBBBA introduced a 100% federal depreciation deduction for certain "qualified production property" — specialized manufacturing and production facility investments — placed in service in 2025 and 2026. Massachusetts has historically decoupled from bonus depreciation under IRC Section 168(k), and it's doing so again here: no full first-year write-off on the state return for this category of asset.
3. Section 179 Expensing Limits
Section 179 lets small businesses expense equipment purchases immediately instead of depreciating them over several years — one of the most commonly used deductions for businesses buying vehicles, machinery, computers, and furniture. OBBBA raised the federal limit from $1.25 million to $2.5 million for 2025 and 2026.
Massachusetts is keeping the old, lower limit for state purposes. If you bought $1.8 million in equipment this year expecting to expense all of it on both returns, you'll need to depreciate the excess over its normal recovery period for Massachusetts — a separate depreciation schedule your bookkeeping needs to track going forward.
4. Business Interest Expense Limitation (Section 163(j))
OBBBA loosened the formula that caps how much business interest expense a company can deduct, by removing depreciation and amortization from the calculation (an EBITDA-based test instead of the more restrictive EBIT-based one). Massachusetts is keeping the older, more restrictive EBIT-based calculation for 2025 and 2026, with alignment to the federal method scheduled to arrive in 2027.
For businesses carrying real debt — commercial real estate, franchise financing, leveraged equipment purchases — this affects how much interest is deductible on the state return, independent of the federal calculation.
The Deadline That Matters: September 10, 2026
If you already filed a 2025 Massachusetts return using the more generous federal treatment for any of the above — full R&E deduction, full bonus depreciation, the higher Section 179 limit, or the loosened interest cap — the state is giving you a narrow window to self-correct.
File an amended Massachusetts return and pay the resulting additional tax by September 10, 2026, and the state won't charge interest on the underpayment. Miss that date, and interest starts accruing on top of whatever additional tax is owed.
This is squarely a "talk to your accountant this month, not in the fall" situation. The provisions most likely to trigger an amendment are the R&E deduction and Section 179 — both are easy to have gotten wrong if your 2025 return was prepared by simply carrying federal numbers onto the state form.
Why This Keeps Happening — and Why It Won't Be the Last Time
Massachusetts isn't unusual here. Because federal tax law changes essentially every year and states move at their own pace, this same conformity gap opens up somewhere every filing season — it just happened to land on some of the most consequential provisions in OBBBA this cycle. If you operate in more than one state, or your accountant works across state lines, don't assume a rule that applies in one state applies in another; each state legislature makes its own call on which federal changes to adopt, delay, or reject outright.
The practical lesson for any small business owner, regardless of state: the federal return is not the whole story. A provision that looks like free money on your Schedule C or Form 1120 might be adjusted, capped, or reversed entirely once it hits your state return.
What to Do Right Now
- Ask whether your business has R&E costs. This term is broader than a formal "R&D department" — software development, product design iteration, and process engineering can all qualify. If your 2025 federal return claimed the immediate R&E deduction or the super deduction catch-up, your Massachusetts return needs a separate five-year amortization calculation.
- Check your Section 179 elections against the $1.25 million Massachusetts cap, not the $2.5 million federal one, if you made large equipment purchases in 2025.
- Review any 2025 extension or estimated payments you made assuming federal treatment would carry through to the state — this is one of the areas CPAs flag as an immediate compliance risk, separate from the amendment deadline itself.
- Get the amended return filed before September 10, 2026 if you find a gap, to avoid interest charges layering on top of the tax due.
- Track state and federal depreciation separately going forward. Once federal and state schedules diverge on an asset, they usually stay diverged until it's fully depreciated — a single combined depreciation schedule will produce the wrong number on one return or the other for years.
Keep State and Federal Books Reconciled From the Start
Situations like this are exactly why maintaining clean, detailed financial records matters — a business that can quickly answer "what did we deduct for R&D in 2025, and under which method" doesn't have to scramble to reconstruct it under a deadline. Beancount.io offers plain-text accounting that gives you complete transparency and full history over every adjustment, including the kind of state-versus-federal divergence that trips up so many small businesses each year. Get started for free and see why developers and finance-savvy business owners are switching to plain-text accounting.