Roth Conversion for Business Owners
A Roth conversion for business owners is a different calculation than it is for a salaried employee, because your income does not arrive in a flat line: pass-through K-1 profits swing year to year, a sale or a down year can drop your bracket for twelve months, and the conversion itself can collide with the 20% qualified business income (QBI) deduction in ways a W-2 employee never faces. That volatility is both the opportunity and the trap.
For a pass-through owner, a Roth conversion is taxed as ordinary income the year you do it, so the goal is to convert in low-K-1 or loss years and stop before conversion income pushes you past the QBI phase-out. For 2026 the 199A threshold is $403,500 MFJ / $201,750 single, above which a specified service business can lose the deduction (Source: IRS Rev. Proc. 2025-32).
Why a Roth conversion for business owners works differently
An employee sees roughly the same W-2 every year, so their bracket is predictable and their only conversion lever is timing around retirement. You have a lever they do not: your taxable income is manufactured, not fixed. Distributions, reasonable compensation, depreciation, a bonus-depreciation asset purchase, a slow quarter, a partner buyout, or a full exit can move your marginal rate by 10 or 20 points in a single year. Every one of those swings is a potential conversion window.
The flip side is that the same income that creates windows also creates traps that are easy to overlook. Conversion income stacks on top of K-1 profit and can silently erase your QBI deduction, trigger the 3.8% net investment income tax (Source: IRC 1411), or set a Medicare surcharge two years out. The winning approach is not converting every year; it is reading the income statement, finding the trough years, and filling the low bracket precisely. See our overview at the Roth conversion service page for how the pieces fit together.
Which of your accounts can be converted, and the 2026 limits that feed them
Business owners typically hold the pre-tax balances that later become conversion candidates inside plans employees rarely have. Any of these can be converted to a Roth IRA (a pre-tax 401(k) can also do an in-plan Roth conversion):
- SEP IRA and SIMPLE IRA from prior self-employed years.
- Solo 401(k) / one-participant 401(k) pre-tax deferrals and profit sharing.
- Traditional IRA rollovers from an old corporate 401(k).
- Cash balance / defined benefit balances, once distributable.
For 2026 the solo 401(k) lets an owner defer up to $24,500 as the employee (plus an $8,000 age-50 catch-up, or $11,250 at ages 60-63), and add employer profit sharing up to 25% of compensation, with total additions capped at the 415(c) limit of $72,000 before catch-up (Source: IRS Notice 2025-67). The IRA limit is $7,500 with a $1,100 catch-up. These are the dollars that build the pre-tax pile you will later meter into a Roth. Details at solo 401(k) contribution limits for 2026.
Roth conversion for S corp owners: reasonable compensation is a hidden lever
Your S-corp W-2 salary is not just a payroll number, it is the base for solo-401(k) contributions and for the QBI wage cap. A higher reasonable salary funds larger pre-tax contributions now (more to convert later) but raises current ordinary income; distributions are lighter but do not count for plan purposes. The 401(a)(17) compensation cap that limits plan contributions is $360,000 for 2026 (Source: IRS Notice 2025-67).
The IRS requires an S-corp shareholder-employee to take reasonable compensation as W-2 wages before non-wage distributions, and can reclassify distributions as wages if the salary is too low (Source: IRS FS-2008-25). For conversion planning that rule cuts two ways. Salary is the only comp that counts toward the solo-401(k) $24,500 deferral and the 25%-of-wages profit-sharing contribution, so a modest salary starves the plan. Salary also drives the 199A wage limitation for high earners, where the QBI deduction is capped at 50% of W-2 wages (or 25% of wages plus 2.5% of unadjusted asset basis) (Source: IRS qualified business income deduction guidance).
The practical read: in a year with a large conversion planned, spiking salary at the same time can be counterproductive, because W-2 wages and the conversion both land in ordinary income and can stack into a worse bracket and past the QBI threshold together. The two decisions belong in one coordinated plan rather than treated as separate files.
Roth conversion SEP IRA pro-rata rule: how your old balances taint a conversion
The pro-rata rule treats all of your traditional, SEP, and SIMPLE IRAs as one pool. If any of it is pre-tax, you cannot cherry-pick after-tax dollars to convert tax-free; each conversion is taxed proportionally. A large SEP IRA from your self-employed years therefore makes a “backdoor” contribution mostly taxable. Solo 401(k) balances are counted separately from IRAs for this test.
Suppose you hold a $190,000 SEP IRA from prior years plus a $10,000 nondeductible traditional IRA contribution. The IRS sees $200,000 total, 95% pre-tax. Converting $10,000 in the hope it is your after-tax money still leaves 95% of it, $9,500, taxable anyway. The workaround owners have that employees often do not: a solo or S-corp 401(k) can accept a rollover of pre-tax IRA and SEP money, emptying the IRA side so the pro-rata pool is clean. Read the mechanics at the pro-rata rule and Roth conversions.
Roth conversion and QBI deduction phase-out: the trap competitors skip
A Roth conversion raises taxable income, and for a pass-through owner that can push you into or through the 199A phase-out and cut or erase the 20% QBI deduction, especially for a specified service business (SSTB). For 2026 the phase-in runs $403,500 to $553,500 MFJ and $201,750 to $276,750 for others (Source: IRS Rev. Proc. 2025-32). Lost deduction plus tax on the conversion can create an effective rate far above your bracket.
This is a commonly under-modeled issue for this persona. Here is why it bites. If you own an SSTB (consulting, law, medicine, financial services, and similar), your QBI deduction fully disappears once taxable income clears the top of the phase-in range, $553,500 MFJ for 2026. A conversion is ordinary income that walks you up that ramp. Every conversion dollar inside the phase-in range does two things at once: it is taxed at your bracket, and it shrinks a 20% deduction on your business profit. The combined effect is the “don’t accidentally pay a 50% rate” problem.
Illustrative example (numbers for illustration only): an SSTB owner files MFJ with $403,500 of taxable income sitting right at the 2026 threshold and $450,000 of QBI. Below the threshold the deduction is roughly 20% of QBI. Converting $150,000 brings taxable income to $553,500, the top of the phase-in, where the SSTB deduction is fully gone. The conversion is taxed as ordinary income and it costs the QBI deduction that $150,000 of income phased out. The nominal bracket might read 32%, but the true marginal cost of those conversion dollars is meaningfully higher once the vanishing deduction is counted.
Two nuances keep this from being a flat “never convert” rule. First, conversion income also raises the overall 199A ceiling (the deduction is limited to 20% of taxable income minus net capital gains), so in some fact patterns the interaction is milder. Second, OBBBA added a minimum $400 QBI deduction for owners with at least $1,000 of active QBI, effective for tax years beginning after 12/31/2025 (Source: IRS Rev. Proc. 2025-32, sec. 4.26). The takeaway is not to avoid conversions; it is that the QBI hit is worth modeling in dollars before converting, and that conversions are often kept below the threshold that starts the phase-out.
Roth conversion in a business loss year: a low-bracket window
A loss or low-income year is a strong conversion window for a business owner. When a net operating loss or a soft year drops your taxable income into a low bracket, converting fills that low bracket with income you would otherwise never see taxed so cheaply. Because conversions are taxed at the year’s marginal rates (Source: IRC 408A), a trough year converts pre-tax dollars at rates you may never see again.
Startup losses, a real-estate depreciation year, a sabbatical, a between-ventures gap, or a genuinely bad sales year all compress your bracket. A common approach is to project taxable income by early Q4, gauge how far the year has fallen below the normal bracket, and size a conversion to fill only that low bracket. A word of caution owners forget: a net operating loss can offset conversion income, which sounds efficient but actually wastes the loss, since the loss is often worth more carried against high-rate future profit, with the conversion filling the low bracket the loss already created. That sequencing is worth modeling before December 31.
Roth conversion ladder strategy: a worked multi-year plan for a pass-through owner
A conversion ladder spreads conversions across several years so each year’s conversion fills a target bracket without spiking into the next one or past the QBI threshold. For a business owner the ladder is keyed to projected K-1 income, not a fixed dollar amount, so more is converted in soft years and little or nothing in peak years. The Dec 31 deadline applies each year (Source: IRS conversion rules).
The table below is an illustrative five-year ladder for an S-corp owner, MFJ, targeting the top of the 24% bracket and staying under the 2026 QBI phase-out start of $403,500. Figures are illustrative only and not a projection of any client result.
| Year | Business situation | Projected taxable income before conversion | Illustrative conversion | Reasoning |
|---|---|---|---|---|
| 1 | Strong K-1 | $390,000 | $0 | Already near QBI threshold; converting would trigger phase-out |
| 2 | Soft year | $210,000 | $180,000 | Fills toward the threshold, keeps QBI intact |
| 3 | Depreciation year | $150,000 | $240,000 | Large deductions open a wide low-bracket window |
| 4 | Recovery | $320,000 | $80,000 | Small top-up under the threshold |
| 5 | Peak / pre-exit | $410,000 | $0 | Above threshold; pause the ladder |
The point of the ladder is that conversion size follows the income statement. Two of five years convert nothing. See how much to convert to Roth and the Roth conversion break-even analysis for the underlying math.
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How much to convert to Roth without changing your tax bracket
With full-year taxable income estimated by early Q4, the gap between that figure and the top of the target bracket, minus a safety cushion for late K-1 adjustments, is what a conversion can fill. For a pass-through owner the harder ceiling is often the 2026 QBI threshold, $403,500 MFJ / $201,750 single (Source: IRS Rev. Proc. 2025-32), not the bracket line itself.
Because K-1 income is frequently not final until the following spring, owners commonly convert against a conservative income estimate and leave headroom. If an owner converts right up to a bracket edge and a late K-1 adjustment adds $20,000 of profit, those conversion dollars retroactively land in the higher bracket. Many owners intentionally stop a bracket or a QBI cushion short and, if the year finishes lower than expected, top up before December 31. The conversion has no dollar or income limit, so the only real constraints are the thresholds you set.
Mega backdoor Roth in a solo 401(k): building Roth instead of converting
Instead of converting a taxable IRA, a business owner can build Roth money directly inside a solo or S-corp 401(k) using after-tax contributions plus an in-plan Roth conversion, the mega-backdoor Roth. It fills the gap between deferrals and the 415(c) limit of $72,000 for 2026 with Roth dollars, and unlike an IRA conversion the after-tax basis converts with little or no tax (Source: IRS Notice 2025-67).
This is an owner-only lever that is easy to overlook. If your plan document allows after-tax (non-Roth) employee contributions and in-plan Roth conversions, you can contribute beyond the $24,500 deferral and profit sharing, up to the $72,000 total, and immediately convert the after-tax slice to Roth. Because it is after-tax basis, converting it is largely tax-free, which sidesteps the whole QBI and bracket problem that a traditional-IRA conversion creates. Not every off-the-shelf solo 401(k) permits this, so the plan document has to be built for it. Compare the two routes at mega-backdoor Roth for high earners and, if you use an in-service move, in-service 401(k) rollovers.
How a cash balance plan changes the picture
Owners running a cash balance (defined benefit) plan alongside a 401(k) face a coordination rule. Under IRC 404(a)(7), if employer defined-contribution money (excluding elective deferrals) does not exceed 6% of aggregate compensation, the combined-deduction limit does not apply; only DC employer contributions above 6% count toward it (Source: IRS “Combined limits under IRC Section 404(a)(7)”). That is why owners with a cash balance plan usually cap profit sharing near 6%. The cash balance balances themselves become pre-tax conversion candidates once distributable. See cash balance plans.
Roth conversion before selling a business: sequencing the exit
A sale year and the year after usually pull in opposite directions. A large capital-gain sale year is generally a poor conversion year because ordinary conversion income stacks on top of the gain and can push an owner through the QBI phase-out and into surtaxes. The low-income “gap” year after a sale, before new income starts, is often a strong window. This is marginal-rate arbitrage, not a fixed rule (Source: IRC 408A).
Whether any specific post-sale year is a good conversion year depends on your state, capital-gains stacking, the 3.8% net investment income tax (Source: IRC 1411), and IRMAA, so it has to be modeled rather than assumed. As a pattern, though: if an owner expects a quiet year or two after the exit while proceeds sit invested and earned income drops, that trough can be a comparatively low-cost conversion window. If part of the proceeds is employer stock, net unrealized appreciation is also worth weighing before rolling anything, since that decision is hard to reverse.
Roth conversion and IRMAA Medicare surcharges: the two-year lookback
Roth conversions raise the modified adjusted gross income that Medicare uses to set premiums, and IRMAA runs on a two-year lookback, so a 2026 conversion can raise your Part B and Part D premiums in 2028. For owners nearing 63, conversion size is commonly set with the surcharge tiers in mind, because a single dollar over a tier line raises premiums for the whole year (Source: IRS/CMS IRMAA rules).
For an owner or spouse within two years of 65, or already on Medicare, the surcharge is a real cost of a large conversion and belongs in the model. The tiers are cliffs, not ramps, so a conversion that clears a threshold by a small amount can cost far more in premiums than the last few thousand dollars were worth. See current tiers at 2026 Medicare IRMAA brackets. Roth balances then help later, because Roth IRA withdrawals are not taxable income and do not feed future IRMAA.
Roth conversion strategies after OBBBA: what changed for owners
OBBBA made the current federal brackets permanent and widened the 199A phase-in range to $150,000 MFJ / $75,000 single for 2026, giving pass-through owners a longer runway before the QBI deduction fully phases out (Source: IRS Rev. Proc. 2025-32). It also added a minimum $400 QBI deduction for active owners. Today’s rates are framed as historically favorable, which is the case owners make for converting now.
Two owner-specific items sit alongside the bracket news. The wider QBI phase-in means an SSTB owner has more room to convert before the deduction hits zero, though the trade-off inside the range still applies. Separately, SECURE 2.0 section 603 requires catch-up contributions to be Roth for high earners whose prior-year FICA wages exceed $150,000, statutorily effective for 2026, with regulators allowing a good-faith transition before strict enforcement (Source: IRS Notice 2025-67; IRS final Roth catch-up regulations, 2025). State income tax and, in some states, a pass-through entity tax (PTET) election under the SALT rules also affect the relative cost of converting in a given year, so state-of-residence timing belongs in the plan.
When does a Roth conversion not make sense for a business owner
A conversion does not make sense when you expect a permanently lower bracket in retirement, when you lack outside (non-retirement) cash to pay the tax, or when the conversion would erase a QBI deduction worth more than the future tax savings. Paying the tax from the converted balance is the classic mistake, because it shrinks the Roth and, if you are under 59.5, can add a penalty (Source: IRS conversion rules).
A conversion is commonly skipped or shrunk when: income will drop for good and the owner will simply be in a lower bracket later; the tax bill would have to come from raiding the IRA itself; a peak-K-1 year would tax the conversion at the top rate and cost the QBI deduction on top; or a large conversion would trip an IRMAA tier or ACA subsidy cliff that costs more than the tax arbitrage is worth. For owners who retire before 65 and buy coverage on the exchange, the interaction with ACA subsidies in early retirement also matters. Paying the conversion tax from outside (non-retirement) funds is generally preferable.
Frequently asked questions
How much can a business owner convert to a Roth without jumping into a higher tax bracket?
With full-year taxable income estimated by early Q4, the amount a conversion can fill is the gap up to the top of the target bracket, minus a cushion for late K-1 adjustments. For pass-through owners the binding ceiling is often the 2026 QBI threshold, $403,500 MFJ / $201,750 single, rather than the bracket edge itself (Source: IRS Rev. Proc. 2025-32). Many owners leave headroom and top up before December 31 if the year finishes low.
Should I do a Roth conversion in a year my business had a loss or low income?
Usually yes, a loss or low-income year is a strong conversion window for a business owner, because conversions are taxed at that year’s marginal rates (Source: IRC 408A). The headroom up to the top of that low bracket is what a conversion can fill. One trap is worth noting: a net operating loss that offsets conversion income can waste the loss, since it is often worth more carried against high-rate future profit.
Will a Roth conversion cost me my 20% QBI deduction?
It can. A conversion raises taxable income, and for a pass-through owner that can push you into or through the 2026 199A phase-in ($403,500 to $553,500 MFJ; $201,750 to $276,750 others), reducing or eliminating the deduction, fully so for a specified service business at the top (Source: IRS Rev. Proc. 2025-32). Owners commonly model the dollar cost first; often the fix is keeping conversions below the threshold.
Can I convert my SEP IRA or solo 401(k) to a Roth, and does the pro-rata rule apply?
Yes to both accounts. The pro-rata rule pools all traditional, SEP, and SIMPLE IRAs, so if any is pre-tax, each conversion is taxed proportionally and you cannot isolate after-tax dollars (Source: IRS conversion rules). Solo 401(k) balances are counted separately from IRAs, and rolling SEP money into a solo 401(k) can clean the IRA pool before a backdoor contribution.
How does my K-1 income affect the timing of a Roth conversion?
Your K-1 sets the year’s bracket, so it drives conversion size. High-K-1 years are poor conversion years because the conversion stacks on already-high ordinary income; low-K-1 years open windows. Because K-1s often are not final until spring, owners commonly convert against a conservative income estimate and leave a cushion, then top up before December 31 if profit came in lower than projected.
Should I do a Roth conversion before or after I sell my business?
Generally after, in the low-income gap year following the sale, not in the high capital-gain sale year itself, where conversion income stacks on the gain and can trigger the QBI phase-out and surtaxes. This is marginal-rate arbitrage and depends on your state, gains stacking, NIIT, and IRMAA, so it should be modeled rather than assumed (Source: IRC 408A).
Is a mega-backdoor Roth through my business 401(k) better than a taxable Roth conversion?
It is a different tool, not strictly better. A mega-backdoor Roth adds after-tax dollars to a solo or S-corp 401(k) up to the 2026 415(c) limit of $72,000 and converts them in-plan with little or no tax, sidestepping the bracket and QBI issues of an IRA conversion (Source: IRS Notice 2025-67). It requires a plan document that allows after-tax contributions and in-plan Roth conversions.
Sources
- IRS Notice 2025-67, 2026 retirement plan and cost-of-living limits (irs.gov)
- IRS Rev. Proc. 2025-32, 2026 inflation adjustments, including section 199A thresholds (irs.gov)
- IRS “One-Participant 401(k) Plans” and “401(k) and profit-sharing plan contribution limits” (irs.gov)
- IRS “Combined limits under IRC Section 404(a)(7)” (irs.gov)
- IRS FS-2008-25, “Wage Compensation for S Corporation Officers” (irs.gov)
- IRS “Qualified business income deduction” (irs.gov)
- IRS net investment income tax guidance and IRC 1411 (irs.gov)
- IRS final regulations on the SECURE 2.0 Roth catch-up rule, 2025 (irs.gov; Federal Register 2025-17865)
- IRC 408A and IRS Roth conversion guidance (irs.gov)