A single-member S-corp with $185,000 of qualified business income, W-2 wages of $42,000, and no unadjusted basis in qualified property claimed a $37,000 qualified business income deduction in 2025 — the 20% deduction that has shaved 4–7 points off the effective rate for pass-through owners since 2018. In the 2026 as-written law, that deduction drops to zero unless Congress extends it. Same revenue, same wages, same building — but about $8,800 more federal income tax at a 24% marginal rate, before state conformity is even considered. For owners who set salary, retirement, and estimated taxes around the QBI math, the cliff is not a future hypothetical; it is next April's estimate.
Section 199A, the qualified business income deduction, is scheduled to sunset for tax years beginning after December 31, 2025, under the Tax Cuts and Jobs Act. As of this writing, extension proposals — including elements of OBBBA and standalone 199A bills — would make the deduction permanent, expand it, or let it expire. The prudent bookkeeping posture in mid-2026 is to model both: file under the law that exists, and plan cash on the law that might.
This guide explains what 199A actually gives you, who hits the W-2/UBIA and specified service trade or business (SSTB) limits, how to model the cliff at your income level, and the moves to consider whether the deduction survives or not — without confusing a temporary tax benefit with a permanent business model.
What Section 199A Gives You — And What It Doesn't
Section 199A allows eligible taxpayers — individuals, trusts, and estates with qualified business income from a qualified trade or business — a deduction of up to 20% of QBI, plus 20% of qualified REIT dividends and qualified publicly traded partnership income, subject to limitations. For most small-business owners, the relevant piece is 20% of QBI.
Key features that surprise owners:
- It is not a business deduction. It is a deduction from taxable income on Form 1040, not on Schedule C or 1120-S. It does not reduce self-employment tax, and it does not reduce QBI itself. Your Schedule C profit is still the SE-tax base; 199A sits below that line.
- It is not automatic at 20%. For owners above threshold amounts, the deduction is limited by W-2 wages and unadjusted basis immediately after acquisition (UBIA) of qualified property, and for SSTBs it phases out entirely. Below thresholds, it is generally the full lesser of 20% of QBI or 20% of taxable income minus capital gains — no wage/UBIA math needed.
- It interacts with other deductions. QBI is net of attributable deductions — unreimbursed partnership expenses, self-employed health insurance allocable to the business, and the deductible portion of SE tax where allocated — so choices about retirement contributions and health arrangements move QBI itself.
For 2025 (the last year before sunset as written), the threshold amounts are indexed — for 2024 they were $191,950 single / $383,900 joint for the start of the phase-in, $241,950 / $483,900 for the end; 2025 thresholds are higher and 2026 would be higher still if extended. If 199A expires, these thresholds become irrelevant — the deduction is simply gone.
For 2026 planning, think in brackets:
- Below threshold: You got the full 20% before; you lose the full 20% if it sunsets.
- In the phase-in band: Your deduction was already partially limited by W-2/UBIA or SSTB status; the cliff is still 100% of whatever you were actually getting, but that "whatever" was already reduced.
- Above threshold / SSTB fully phased out: You were already at zero; sunset changes nothing — your post-cliff rate is already your reality.
The W-2 Wage and UBIA Limits — The Math That Decides Your Number
Above the threshold, the deductible amount for each qualified trade or business is the lesser of:
- 20% of QBI from that business, or
- The greater of:
- 50% of W-2 wages from that business, or
- 25% of W-2 wages + 2.5% of UBIA of qualified property
That is per-business, then summed and capped by 20% of taxable income.
Why this matters for the cliff model. An S-corp owner who kept W-2 salary low to maximize 199A below threshold will face a different post-cliff trade. Today a $30,000 salary on $180,000 QBI may maximize the current deduction (no wage limit below threshold), but if 199A disappears, the salary decision reverts to reasonable compensation plus payroll-tax and qualified-plan contribution math, not QBI optimization. Conversely, an owner who raised salary to satisfy the 50% wage test while in the phase-in band may be able to lower salary modestly if the reason for that salary level disappears — but reasonable-compensation rules don't disappear with 199A.
UBIA — the original cost of qualified depreciable property still within its depreciable period — rewards capital-intensive businesses (real estate, manufacturing, trades with equipment) that otherwise have low W-2. A landlord with a $600,000 building and $12,000 of W-2 can still support a 199A deduction via 2.5% of UBIA ($15,000) where wages alone would cap it at $6,000. If 199A sunsets, that UBIA-support logic vanishes with it.
SSTBs — Where the Cliff Is Steeper
A specified service trade or business includes health, law, accounting, actuarial science, performing arts, consulting, athletics, financial services, brokerage, and any business where the principal asset is the reputation or skill of one or more employees or owners — plus a catch-all. Engineering and architecture were explicitly excluded from SSTB status.
For SSTBs:
- Below threshold: Full 20% as usual.
- In the phase-in: The QBI, W-2, and UBIA from the SSTB phase out proportionally.
- Above the top of the phase-in: Zero deduction from that SSTB — QBI from that business is simply out.
The cliff for an SSTB owner whose taxable income sits inside the phase-in band is especially sensitive to taxable-income management. A $12,000 deductible retirement contribution that drops taxable income $12,000 deeper into the phase-in can restore several thousand dollars of QBI deduction in the last year 199A exists — and becomes pure rate arbitrage (deduction at marginal rate) the year after sunset. Year-end income timing matters more in 2025 than it will in 2026 if the deduction goes away.
Modeling the Cliff — Three Archetypes
1. The solo consultant (SSTB), single filer, $165,000 taxable income in 2025, QBI $140,000, no W-2/UBIA issue below threshold:
- 2025 deduction: ≈ $28,000 (20% × $140,000, under the taxable-income cap)
- 2026 if sunsets: $0 → additional taxable income $28,000 → ≈ $6,720 more tax at 24%
- Planning note: The entire benefit was SSTB-contingent on staying below threshold. 2026 income management no longer buys a QBI benefit — it buys only the normal bracket benefit.
2. The S-corp trades business, joint filers, $390,000 taxable income, QBI $185,000, W-2 $42,000:
- 2025 (in phase-in): deduction limited by wages — greater of 50%×$42,000=$21,000 vs. 25%×$42,000+2.5%×UBIA (assume $400K UBIA → $10,500+$10,000=$20,500) → cap $21,000 vs. 20%×$185,000=$37,000 → deduction $21,000
- 2026 if sunsets: $0 → additional taxable income $21,000 → ≈ $5,040 at 24%, ≈ $6,720 at 32% if the extra income pushes into the next bracket
- Planning note: That $42,000 salary was partially a 199A support decision. Post-sunset, revisit salary against reasonable comp, payroll tax, and Solo 401(k) contribution capacity — the QBI wage test no longer justifies the level.
3. The rental with triple-net leases, joint filers, QBI $90,000, W-2 $0, UBIA $620,000:
- 2025: cap = 25%×0 + 2.5%×$620,000 = $15,500 vs. 20%×$90,000=$18,000 → deduction $15,500
- 2026 if sunsets: $0 → additional taxable income $15,500
- Planning note: Real-estate QBI often relied on UBIA more than wages. If 199A goes, the UBIA-tracking discipline still matters for depreciation, but no longer for a deduction.
Run your own numbers with two columns — 2025 deduction actually claimed and 199A at zero — and extend taxable income so you can see the marginal rate on the clawed-back deduction. The number that matters is not "I lose 20% of QBI" but "I lose my actual capped 199A and it is taxed at my next marginal rate."
Moves to Consider Whether It Expires or Is Extended
Treat these as modeling inputs, not as instructions to chase a deduction that may not exist next year.
Compensation and retirement — re-optimize without the QBI overlay:
- Reasonable compensation remains the standard for S-corps. Don't hold an artificially high salary solely to satisfy a W-2 test that no longer exists if sunset occurs. Conversely, don't cut salary to the bone — the reasonable-comp standard and Social Security wage-base planning persist.
- Retirement contributions (SEP, Solo 401(k), SIMPLE — see the companion guide) reduce taxable income and — while 199A existed — could reduce QBI and the taxable-income cap. After sunset, they are pure above-the-line/income adjustments at your marginal rate. The right 2025 contribution may be slightly lower to preserve QBI and the taxable-income cap in the last deduction year; the right 2026 contribution is whatever maximizes after-tax wealth at the new rate structure.
- Health arrangements — Self-employed health insurance and HRA/ICHRA choices that were partly QBI decisions become straightforward deduction and credit decisions post-sunset.
Entity and aggregation — less 199A-specific engineering:
- Aggregation elections under Reg. §1.199A-4 let you aggregate trades or businesses for the W-2/UBIA test when you meet the common-ownership and other tests. If 199A disappears, aggregation no longer matters — but keep the election records, because a retroactive extension would make them relevant again for amended returns.
- Entity choice — The 2018–2025 calculus that favored pass-through over C-corp at certain income levels because of 199A shifts if the deduction goes away and C-corp rates remain 21%. Model pass-through at the post-cliff rate vs. C-corp at 21% plus a second tax on dividends at your holding period — for many small businesses the pass-through still wins, but the margin narrows and the answer becomes more fact-specific.
Income timing — 2025 vs. 2026 matters more than usual:
- If 199A sunsets, accelerating income into 2025 (where 20% is deductible) and deferring deductions into 2026 (where they are worth more against a higher taxable base) can be directionally helpful — the opposite of the usual defer-income pattern. Accelerating invoicing, delaying discretionary expenses, and timing equipment purchases around Section 179/bonus vs. QBI interaction deserves a two-year model, not a December guess.
- If extension appears likely, the opposite timing may be preferable. Build the two-scenario model now so a late-December legislative update is a parameter change, not a new analysis.
State conformity — the second cliff:
States conform to 199A inconsistently. Some conform fully, some decouple and disallow the deduction, and some conform as of a fixed IRC date that may or may not include an extension. A federal extension does not automatically restore a state deduction — and a federal sunset does not automatically cost you a state deduction that was already decoupled. Track federal and each filing state's 199A position separately.
A Close That Fits Year-End
October–November: Lock the actual 199A claimed for 2025 by business (QBI, W-2, UBIA, SSTB status) and produce the two-column 2026 model (with and without 199A) at your projected taxable income. This is the page your preparer and your estimated-tax calculation both need.
December: Execute timing moves only after the two-column model is signed. If legislation is still pending, execute only the moves that win in both scenarios or are reversible (retirement contribution timing, invoicing discipline) and defer irrevocable structural changes.
January: Reset 2026 estimates on the post-cliff rate if sunset is the law on January 1 — waiting until April to discover the extra taxable income is how underpayment interest happens. If Congress later extends retroactively, you amend; estimates based on the law that exists are never penalized for being wrong about the law that might have been.
The Bookkeeping Connection
Section 199A rewarded — and its cliff punishes — the habit that makes plain-text accounting powerful: income, W-2, UBIA, SSTB status, and taxable income are not abstract tax concepts but dated, business-tagged facts in the ledger. When QBI by trade or business, W-2 by business, UBIA by asset, and owner compensation live in the same version-controlled record, the story from "$185,000 of qualified business income" to "$21,000 deduction in 2025, zero in 2026 as written, $5,040 of tax at 24%" is traceable and explainable to a preparer who must file the last year of a temporary provision from your records, not your memory.
Simplify Your Financial Management
A temporary deduction should not permanently complicate your books — but while it exists, and whether it disappears, the accounting that tracks it should be explicit. Beancount.io gives you plain-text, version-controlled accounting where QBI by business, W-2 and UBIA, and taxable-income timing stay explicitly linked — no hidden spreadsheets, no vendor lock-in, and AI-ready when you want help turning last quarter's income into next year's rate. Get started for free and model the cliff before it models you.