Whether a Roth conversion helps or hurts your QBI deduction comes down to one number: your taxable income relative to the 2026 Section 199A threshold. The same conversion dollar can unlock a deduction the “20% of taxable income” cap was holding back, or it can push a pass-through owner into the phaseout and shrink the 20% deduction. This piece maps that single pivot so a business owner can locate themselves before converting.
A Roth conversion does not change your qualified business income figure, but it raises taxable income, which drives the second half of the Section 199A limit. If your “20% of taxable income” cap is currently binding, conversion income can enlarge the deduction. If you are near or above the threshold, the same income can phase it down or, for a specified service business, erase it.
Does a Roth conversion reduce my QBI deduction?
It depends entirely on which side of your taxable-income threshold the conversion lands you. The Section 199A deduction is the lesser of two limits: 20% of your qualified business income (QBI), or 20% of taxable income minus net capital gain. Converting existing IRA dollars does not touch the QBI figure itself. It moves taxable income, the other cap, and that is where the interaction lives.
Stated plainly, the two-limit rule is: QBI deduction = lesser of (20% of QBI) OR (20% of taxable income minus net capital gain). When taxable income is low, the second limit is the smaller (binding) number, and a conversion that lifts taxable income can lift the deduction with it. When taxable income is high, the phaseout rules built into the first limit take over, and conversion income can work against you.
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One clarification worth isolating: this is about converting an existing IRA. Roth employer contributions to a solo 401(k) are a different animal, because a business-level retirement contribution reduces QBI directly. An IRA conversion does not. Sizing decisions belong in the same conversation as how much to convert to Roth and your target Roth conversion strategy.
The 199A taxable-income thresholds that decide everything (2026)
Section 199A hangs on a taxable-income threshold that is indexed annually. For 2026, under IRS Revenue Procedure 2025-32, the full-deduction lines sit at $201,750 for single filers and $403,500 for married filing jointly. Above those lines, wage and specified-service limits phase in. Conversion income stacks on top of your other taxable income and pushes you rightward across these lines.
2026 full-deduction lines: $201,750 single / $403,500 MFJ
Below these taxable-income figures, the full 20% deduction is available with no wage test and no specified-service restriction. This is the zone where a conversion is most likely to help rather than hurt.
2026 phase-in ranges (widened by OBBBA)
The One Big Beautiful Bill Act (P.L. 119-21) widened the phase-in range starting in 2026: $75,000 for single filers (from $201,750 to $276,750) and $150,000 for joint filers (from $403,500 to $553,500). A wider range means the deduction reduces more gradually per dollar of income inside it, compared with the older $50,000 single and $100,000 joint ranges.
| 2026 Section 199A | Single / HOH | Married filing jointly |
|---|---|---|
| Full 20% deduction up to | $201,750 | $403,500 |
| Phase-in range width (OBBBA) | $75,000 | $150,000 |
| Deduction fully limited above | $276,750 | $553,500 |
| Minimum deduction (QBI at least $1,000 + material participation) | $400 | $400 |
SSTB versus non-SSTB: why the same line means two different things
A specified service trade or business (SSTB), think health, law, consulting, financial services, and similar fields, loses the deduction entirely once taxable income clears the top of the phase-in range. A non-SSTB does not vanish. Instead, above the threshold it becomes subject to the W-2 wage and 2.5% UBIA (unadjusted basis) limit, which can trim the deduction to a “haircut” rather than a total loss if wages or property are thin.
Where does conversion income enter?
Conversion income is ordinary income in the year you convert. It does not change QBI, but it raises taxable income, moving you rightward across every line above. That is the whole mechanism: the conversion is a lever on the taxable-income side of the 199A calculation, and the direction it pushes the deduction depends on where you start.
When conversion income helps: unlocking a capped deduction
When taxable income sits below your QBI, the “20% of taxable income minus net capital gain” limit is the smaller number, so it caps the deduction below its full potential. Adding ordinary income, such as a measured Roth conversion, lifts that cap toward 20% of QBI and can restore deduction that was otherwise left on the table, provided you stop short of the threshold.
The scenario
One common case involves an owner whose QBI is larger than taxable income. Perhaps other deductions, a down business year for a spouse, or large itemized deductions have compressed taxable income. The 20% of QBI figure looks generous, but the 20% of taxable income figure is smaller, and the smaller number wins. Deduction is being lost simply because taxable income is low.
Worked example (illustrative)
Steve, single, has $200,000 of QBI but only $140,000 of taxable income (assume no net capital gain). His deduction is the lesser of 20% of QBI ($40,000) and 20% of taxable income ($28,000), so $28,000. A $60,000 conversion lifts taxable income to $200,000, just under the $201,750 line. Now 20% of taxable income is $40,000, matching 20% of QBI, and the full $40,000 deduction is restored. That is $12,000 of additional deduction attributable to the conversion, an offset against the tax on the converted dollars. Figures are illustrative and assume no other limits apply.
The “convert up to the threshold” ceiling
The helpful zone has a hard stop: the full-deduction line. In Steve’s case, converting past roughly $201,750 of taxable income starts eating into phaseout territory rather than adding deduction. This is the same “fill the bracket, then stop” discipline that governs a good Roth conversion break-even analysis and multi-year conversion ladder planning.
When conversion income hurts: shrinking or erasing the deduction
For a business owner already near or above the 2026 threshold, conversion income runs the other way. Inside the phase-in range it triggers a partial reduction of the deduction; for an SSTB, income above the top of the range can zero it out. The true cost of the conversion then includes a hidden second layer: the value of the QBI deduction it displaces.
The scenario
An SSTB owner, or a non-SSTB owner limited by W-2 wages, sitting at or just under the threshold has little room. Any ordinary income added on top, including a conversion, walks them into the phaseout. Here the question is not “how much deduction can I unlock” but “how much am I willing to give up.”
How a conversion inside the phase-in range reduces the deduction
Within the range, the deduction is reduced by an applicable percentage equal to the taxable income above the threshold divided by the range width ($75,000 single, $150,000 joint). A conversion that carries you, say, one-third of the way through the range reduces the SSTB deduction by roughly one-third. For a non-SSTB, the same movement phases in the W-2 wage and UBIA limitation instead.
The SSTB cliff
Carrying an SSTB owner’s taxable income above $276,750 single or $553,500 joint erases the deduction entirely. A conversion sized without regard to that ceiling can turn a 20% deduction into a zero in a single tax year.
The true marginal cost math
When a conversion costs deduction, the converted dollar is taxed at your ordinary bracket and carries the value of the lost QBI deduction (20% of the affected QBI multiplied by your rate). An SSTB deduction only fully vanishes above the top of the phase-in range, where a single owner sits in the 32% bracket or higher. For an owner with $300,000 of QBI at a 32% rate, a fully lost 20% deduction is $60,000 of deduction, worth $19,200 in real tax. That $19,200 is the hidden second tax layered on top of the ordinary tax on the conversion itself. Illustrative only.
The decision rule: sizing a conversion around your QBI line
The planning payoff is a simple sequence: identifying pre-conversion taxable income, locating it against the 2026 threshold, considering whether the “20% of taxable income” cap is binding (which tends to help) or the threshold sits above it (which tends to hurt), and then sizing the conversion accordingly. The aim is understanding which regime applies before converting, not after.
Step 1: computing taxable income before conversion
Many owners begin with taxable income before any conversion and before the QBI deduction itself. One approach is locating that number against the 2026 line ($201,750 single, $403,500 joint). The distance to the line represents the available working room.
Step 2: is your 20% of taxable income cap binding?
If taxable income is below QBI, the taxable-income cap is likely binding, and a conversion up to the threshold may enlarge the deduction. If taxable income already exceeds QBI and sits near the threshold, added income tends to phase the deduction down instead.
Step 3: non-SSTB with wage or UBIA headroom versus SSTB
A non-SSTB owner with ample W-2 wages or qualified property may keep much of the deduction above the threshold, giving more tolerance for conversion income. An SSTB owner has the tighter constraint, because the deduction disappears completely past the top of the range.
The “fill to the threshold” heuristic
Many business owners consider filling taxable income up to, but not through, the 199A line, then repeating across several years. Partial multi-year conversions can respect the threshold each year in a way one large conversion cannot. Timing matters too: RMDs must come out first in an RMD year and cannot be converted, so many owners coordinate with 2026 RMD rules and the December 31 conversion deadline.
Why some households model the neighboring effects
A conversion near the 199A line rarely acts alone. Raising taxable income and MAGI can expose other investment income to the 3.8% net investment income tax, lift future Medicare premiums through IRMAA (2026 surcharges begin above $109,000 single / $218,000 joint MAGI, on a two-year lookback), and interact with the OBBBA $400 minimum QBI deduction floor. Modeling these together is where the real answer lives.
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Q3 Advisors is a registered investment adviser focused on retirement tax planning. This page is educational and is not advice; consult a qualified professional.
Frequently asked questions
What are the exact 2026 Section 199A thresholds and where do the phaseouts end?
For 2026, the full 20% deduction is available up to $201,750 of taxable income for single filers and $403,500 for married filing jointly (Rev. Proc. 2025-32). After OBBBA widened the ranges, the deduction is fully limited above $276,750 single and $553,500 joint. Between those points, the limits phase in.
How much QBI deduction is lost when taxable income sits below QBI, and how much conversion restores it?
In the illustrative example, $200,000 of QBI with only $140,000 of taxable income yields a $28,000 deduction (20% of taxable income), not the full $40,000 (20% of QBI). A $60,000 conversion lifts taxable income to $200,000 and restores the full $40,000, adding $12,000 of deduction. Figures are illustrative.
What is the “hidden second tax” for an owner with $300,000 QBI at a 32% rate?
A fully lost SSTB deduction only occurs above the top of the phase-in range, where a single owner is in the 32% bracket or higher. If a conversion fully displaces the deduction, the lost 20% of $300,000 QBI is $60,000. At a 32% marginal rate that is $19,200 of real tax, layered on top of the ordinary tax on the conversion. Illustrative only.
For an SSTB owner, where in the range does the deduction reduce, and where does it hit $0?
For an SSTB, conversion income inside the phase-in range ($201,750 to $276,750 single, $403,500 to $553,500 joint) reduces the deduction by the applicable percentage. The deduction reaches exactly $0 once taxable income exceeds the top of the range: $276,750 single or $553,500 joint in 2026.
How wide is the 2026 phase-in range, and how does that change the per-dollar reduction rate?
OBBBA widened the 2026 phase-in range to $75,000 for single filers and $150,000 for joint filers, up from $50,000 and $100,000. A wider range spreads the reduction over more dollars, so each dollar of income inside the range removes a smaller share of the deduction than under the pre-OBBBA ranges.
Does conversion income change QBI itself or only the taxable-income cap?
For an IRA conversion, only the taxable-income cap. Qualified business income measures income from your trade or business; converting IRA dollars does not add to or subtract from it. The conversion moves taxable income, which is the second half of the 199A limit and the source of the entire interaction.
How does a conversion interact with NIIT and IRMAA?
A Roth conversion is not itself net investment income, so it is not directly subject to the 3.8% NIIT. But it raises MAGI, which can pull other investment income above the NIIT thresholds and can lift Medicare Part B and D premiums through IRMAA on a two-year lookback. Both belong in the model.
What is the OBBBA $400 minimum QBI deduction floor?
Starting in 2026, a taxpayer with at least $1,000 of aggregate QBI from active qualified businesses in which they materially participate receives a minimum deduction of $400 (indexed after 2026), or the regular calculated amount if greater. Even where a conversion compresses the standard calculation, an eligible owner keeps at least that floor.
Do Roth employer contributions to a solo 401(k) reduce QBI, unlike an IRA conversion?
Employer retirement plan contributions are a business-level deduction, so they generally reduce net business income and therefore QBI, roughly dollar for dollar. That is a different lever from an IRA conversion, which does not touch QBI. Designated Roth treatment adds nuance, so this is an area to confirm with a qualified tax professional.
