Idaho just told equipment-heavy businesses: good news, bad news. The good news is Congress made 100% bonus depreciation permanent again under the One Big Beautiful Bill Act, and expanded a brand-new category of full expensing for factory construction. The bad news, if you're filing an Idaho return, is that none of that applies to you.
On February 10, 2026, Governor Brad Little signed House Bill 559, updating Idaho's conformity to the federal Internal Revenue Code as of January 1, 2026, retroactive to January 1, 2025. Idaho does this every year — it's routine housekeeping that keeps the state tax code in sync with whatever Congress changed. Most years it's a formality. This year it isn't, because 2025 is the year the One Big Beautiful Bill Act rewrote federal depreciation rules from the ground up, and Idaho decided to opt out of the two biggest pieces.
If you bought equipment, machinery, or a new production facility in Idaho expecting the same tax break you'd get on your federal return, you need to know exactly where the state diverges — and how to avoid a surprise addition to your Idaho taxable income.
What HB 559 Actually Does
Idaho's default posture is to adopt federal tax law automatically each year through what's called "rolling conformity" — but with specific carve-outs the legislature bolts on top. HB 559 is this year's carve-out list, and it splits federal depreciation and expensing changes into two very different buckets.
The good news: Section 179 gets full conformity
Idaho fully adopts the OBBBA's expanded Section 179 small business expensing limits. For property placed in service after December 31, 2024, the annual expensing cap rises to $2.5 million, with the phaseout threshold starting at $4 million. If your business bought under that ceiling — a delivery van, shop equipment, computers, office furniture — you can deduct the full cost on both your federal and Idaho returns with no adjustment needed. The Tax Foundation estimates this conformity alone saves Idaho businesses roughly $6 million in tax year 2026.
The bad news: bonus depreciation stays decoupled
Idaho will remain decoupled from Section 168(k) bonus depreciation — this isn't new for 2026, it's a continuation of a position Idaho has held since the mid-2000s. What's new is the stakes: the OBBBA permanently reinstated 100% bonus depreciation for qualified property acquired after January 19, 2025, replacing the phase-down schedule that was set to shrink bonus depreciation to 40% and then 0% over the next few years. Idaho businesses now get none of that upside on their state return. The Tax Foundation projects this decoupling will cost Idaho businesses about $151 million in additional state tax liability in tax year 2026 alone, compared to what they'd owe if Idaho had conformed.
The new decoupling: Section 168(n) qualified production property
The OBBBA also created a new category under Section 168(n): 100% expensing for "qualified production property" — essentially the real property (not just equipment) used in manufacturing, when specific requirements around construction dates and use are met. It's aimed squarely at incentivizing new U.S. factory construction. HB 559 decouples Idaho from this provision too, so a manufacturer that expensed a new production facility's construction costs federally will need to add that deduction back for Idaho purposes and depreciate the building on a normal schedule instead.
The R&E wrinkle
HB 559 also decouples from the OBBBA's transition relief under Section 70302 for domestic research and experimental expenditures incurred between 2022 and 2024. Federally, businesses got a faster path to recovering those costs. For Idaho purposes, that R&E spending must continue to be amortized over the remaining period set by the 2017 Tax Cuts and Jobs Act — no acceleration.
Who This Actually Hits
If your business doesn't buy much equipment, or everything you buy falls under the $2.5 million Section 179 cap, HB 559's decoupling provisions may never touch your return. This is squarely an issue for:
- Manufacturers and equipment-heavy operations — machine shops, food processors, printers, fabricators — anyone whose capital purchases regularly exceed Section 179 limits or who leases/finances large equipment packages
- Companies constructing or expanding a production facility in Idaho, who would have relied on Section 168(n) to expense the building itself
- Businesses with ongoing domestic R&E spend from 2022–2024 still working through TCJA amortization schedules
If you're a service business, a small retailer, or a freelancer whose biggest asset purchase this year was a laptop, this is mostly background noise — your Section 179 deduction is unaffected either way.
The Mechanics: How the Addback Actually Works
Idaho's bonus depreciation decoupling isn't a permanent loss of the deduction — it's a timing difference. Here's how it plays out on the return:
- Compute Idaho depreciation as if you'd never claimed bonus depreciation. You (or your preparer) run a second, parallel Form 4562 calculation using regular MACRS depreciation instead of the federal bonus/full-expensing amount.
- Add back the difference. Whatever extra depreciation you claimed federally via Section 168(k) or 168(n) gets added back as Idaho taxable income in the year of purchase, on Form 41 (corporations), Form 41S (S corporations), or the individual equivalent.
- Track it forward. Idaho's Form DBDA (Deferred Bonus Depreciation Addition) exists specifically to track your cumulative addback and the subtraction you're entitled to recover in later years.
- Recover it as a subtraction over time — or at sale. Because Idaho still lets you depreciate the asset on its normal MACRS schedule going forward, you get the deduction back gradually across the asset's useful life, and any remaining basis difference gets trued up through gain/loss recapture when the asset is eventually sold or disposed of.
The net effect: you still get the full deduction eventually, just spread out instead of taken all at once. For a business with steady, predictable capital spending, this mostly just changes when the cash-flow benefit of lower taxes shows up — but for a business making one large purchase (a new production line, a facility buildout), it can mean a real near-term cash tax hit at the state level that federal planning didn't account for.
What to Do Before You File
- Don't assume federal and state depreciation match. If your accounting software or bookkeeping system tracks only one depreciation schedule tied to your federal return, you're set up to misstate Idaho taxable income the moment bonus depreciation or Section 168(n) is involved.
- Run the parallel Form 4562 the moment you place qualifying property in service — not at filing time. Retroactively reconstructing a "what would MACRS-only depreciation have been" schedule months later, across multiple assets, is exactly the kind of task that turns into hours of error-prone spreadsheet archaeology.
- Talk to your Idaho preparer specifically about Form DBDA if you have any bonus-depreciation or qualified-production-property addbacks outstanding from prior years, since Idaho's decoupling isn't new — some businesses may already be carrying deferred additions forward without realizing it.
Keep Your Depreciation Schedules Straight From Day One
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