Solo 401(k) to Roth IRA Conversion: The Self-Employed Guide (2026)

Self-employed professionals — consultants, freelancers, sole proprietors, and S-corp owner-employees — who hold a solo 401(k) have conversion advantages that W-2 workers don't get. The balance is isolated from the IRA pro-rata pool, the wind-down income decline can span a decade of improving bracket room, and ages 60–63 come with a super catch-up contribution that lets you move $35,750/year into Roth status without a conversion event at all. This guide covers all three conversion paths, the pro-rata isolation benefit, and how to size conversions to stay below IRMAA thresholds across a multi-year wind-down.

Who has a solo 401(k)?

A solo 401(k) — also called a one-participant 401(k) or individual 401(k) — is available to self-employed individuals with no full-time employees other than a spouse. Eligible business structures include:

• Sole proprietors and single-member LLCs filing Schedule C
• S-corp owner-employees who draw a W-2 salary from their own company
• Partners in a small partnership with no non-partner employees

If you've been self-employed for 10–25 years, you may have accumulated $400K–$2M in pre-tax solo 401(k) assets. That balance will become ordinary income eventually — either when you convert it to Roth on your own schedule, or when the IRS forces distributions as RMDs starting at 73 or 75. The question is which brackets you pay those taxes in.

Three ways to Roth-ify a solo 401(k)

Path 1: Roll the pre-tax balance directly to a Roth IRA

A solo 401(k) can be rolled directly to a Roth IRA, making the converted amount ordinary income in the year of the transfer. Key mechanics:

• No mandatory 20% withholding on a trustee-to-trustee transfer. The plan sends assets directly to the Roth IRA custodian without the check passing through your hands. The 20% withholding trap (IRC § 3405(c)) that applies when you receive a 401(k) distribution as a check does not apply to direct transfers.¹
• Requires a distributable event: separation from service (you've wound down the business), plan termination, or age 59½ (which allows in-service distributions from most plan documents).
• Partial rollovers allowed. You can roll $70,000 this year and $70,000 next year, treating each as a partial annual conversion — the most tax-efficient approach for large balances.
• No dollar cap. Unlike Roth IRA contributions (income-limited and capped at $7,500 in 2026), qualified plan rollovers to Roth IRA have no maximum. You can convert $600,000 in a single year if the tax cost is acceptable.

Path 2: In-plan Roth conversion within the solo 401(k)

If your plan document permits it — most custodians' self-employed plans now do — you can convert the pre-tax solo 401(k) balance to a Roth sub-account within the same plan. The tax treatment is identical: the amount converted is ordinary income in the year of conversion. Advantages of staying in-plan:

• ERISA creditor protection remains in place (stronger than IRA protection in many states).
• No custodian transfer required; funds don't leave the plan.
• Useful if you want to keep future Roth distributions in the plan (e.g., creditor protection in litigation-prone professions).

The main drawback is that a Roth sub-account within a solo 401(k) may have fewer investment options than a Roth IRA at a brokerage of your choice.

Path 3: Make Roth contributions going forward (while still contributing)

If you still have self-employment income, you can elect to make employee deferrals as Roth (after-tax) contributions to your solo 401(k). This is not a conversion — it's contributions of already-taxed income. Employer profit-sharing contributions must still go in pre-tax; there is no Roth option for the employer side.

This path is most valuable for professionals ages 60–63, who qualify for the SECURE 2.0 super catch-up: a total employee deferral of $35,750 in 2026 (the $24,500 base plus $11,250 super catch-up).² Making those deferrals as Roth moves $35,750/year into tax-free status without triggering a taxable conversion event — you pay tax on income you were already earning anyway.

The pro-rata rule advantage

One of the most significant differences between a solo 401(k) and a SEP-IRA is how each interacts with the pro-rata rule.

Under IRC § 408(d)(2), any conversion from a traditional IRA to a Roth IRA must pull proportionally from all IRA assets — including deductible and non-deductible amounts in all traditional, SEP, and SIMPLE IRAs you own. A solo 401(k) balance is not an IRA. It is completely excluded from that aggregation pool.

This reverse-direction strategy — rolling an IRA into the solo 401(k) to clear the pro-rata pool — only works while you still have self-employment income and an active solo 401(k). Once the plan is terminated or the business is closed, the window closes.

The self-employed wind-down window

Unlike employees who retire on a specific date, self-employed professionals often wind down over years — cutting client loads, raising project minimums, or transitioning to advisory-only roles. Each step down in SE income opens more room for conversions at lower marginal rates.

For those born in 1960 or later, the RMD clock doesn't start until age 75 (SECURE 2.0 § 107). A self-employed professional who retires at 62 has a 13-year window — one of the longest Roth conversion runways available.

Worked example: Elena, age 65, management consultant

Elena is a 65-year-old sole proprietor who has been self-employed for 22 years. She has $680,000 in her solo 401(k) — all pre-tax — and no traditional IRA. She's winding down to part-time consulting: $40,000 in gross SE income this year. She just enrolled in Medicare, is a single filer, and is delaying Social Security to age 70.

Year 1 income and bracket math:

• SE tax deduction (½ × SE tax on 92.35% of $40K): ~$2,827 // IRS Schedule SE; 2026 SE rate 15.3%
• AGI before conversion: ~$37,173
• Standard deduction (single, age 65+): $16,100 + $2,050 = $18,150 // IRS Rev. Proc. 2025-32
• Taxable income before conversion: $37,173 − $18,150 = ~$19,023
• 12% bracket ceiling (single taxable income): $50,400 → room: $31,377 // IRS Rev. Proc. 2025-32
• 22% bracket ceiling: $105,700 → room above 12%: $55,300

IRMAA ceiling: IRMAA Tier 1 starts at $109,000 MAGI for single filers.³ Her MAGI before conversion is ~$37,173. Maximum conversion without triggering IRMAA: $109,000 − $37,173 = $71,827.

Elena converts $70,000 from her solo 401(k) to a Roth IRA via direct trustee-to-trustee transfer:

• New taxable income: $19,023 + $70,000 = $89,023
• Tax in 12% bracket (from $19,023 to $50,400): $31,377 × 12% = $3,765
• Tax in 22% bracket (from $50,400 to $89,023): $38,623 × 22% = $8,497
• Federal tax cost of conversion: $12,262 on $70,000 = 17.5% effective rate

She pays $12,262 from a taxable brokerage account — not by withholding from the conversion itself — preserving the full $70,000 in the Roth IRA to grow tax-free.

10-year projection: At $70,000/year in conversions, Elena converts her $680,000 over roughly 10 years. As her part-time income declines further, the effective rate on later-year conversions drops toward 15–16% (since the 12% bracket fills more of each conversion). She finishes around age 74–75, just as RMDs would have started, having converted the entire balance at an average of roughly 17% rather than 22–26% inside her projected RMD bracket.

No-conversion comparison: If the $680,000 grows at 6% untouched for 10 years, it reaches ~$1.22M. First RMD at 75 (ULT divisor 24.6): $49,593. Added to Social Security she delayed to 70 (~$32,000/year), 85% of SS becomes taxable ($27,200), and her total taxable income is already well into the 22% bracket before IRMAA surcharges. She's also lost the ability to time or manage the tax — distributions are mandatory at the IRS schedule.

Plan termination: the full-conversion decision

When a self-employed professional permanently closes their business, they must eventually terminate their solo 401(k) plan. Plan termination triggers a distributable event that allows a full rollout. Options at termination:

1. Roll to traditional IRA — tax-deferred, no immediate taxes. Good if you want to spread conversions over future years rather than crystallizing all the income at once.
2. Roll directly to Roth IRA — the entire pre-tax balance becomes ordinary income in the termination year. Attractive if income is unusually low that year (final wind-down year, pre-Medicare, below ACA cliff).
3. Roll to a new employer's plan — if you later take a W-2 job, some employer plans accept rollovers, preserving the plan-level creditor protection.

Super catch-up contributions at ages 60–63

SECURE 2.0 § 109 created a "super catch-up" for 401(k) plan participants ages 60–63. For 2026, solo 401(k) holders in this age range can contribute:²

• Employee deferral base: $24,500
• Super catch-up (ages 60–63 only): +$11,250
• Total employee deferral: $35,750
• Total §415 limit (including employer profit-sharing at 25% of compensation): $72,000

If you still have SE income and make these deferrals as Roth contributions, you're moving $35,750/year into tax-free status at your current marginal rate — without a separate conversion event. Combined with partial conversions of the existing pre-tax balance, a professional at 61–63 can be running two parallel strategies: making Roth contributions on current income while converting prior-year accumulations.

Solo 401(k) vs. SEP-IRA for Roth conversions

Both plans serve self-employed professionals, but they differ in Roth flexibility:

Step-by-step: converting your solo 401(k) to Roth IRA

1. Confirm the distributable event. Are you over 59½? Have you separated from service or terminated the plan? Most solo 401(k) plans allow in-service distributions at 59½; check your plan document.
2. Calculate your conversion target. Use the tax bracket calculator to find how much fills the 22% bracket without spillover, then cross-check against the IRMAA calculator. Your target is the lower of the bracket ceiling and the IRMAA Tier 1 threshold ($109K single / $218K MFJ MAGI).
3. Request a direct trustee-to-trustee transfer. Contact your solo 401(k) custodian, specify the dollar amount, and request a direct transfer to your Roth IRA. Explicitly elect zero withholding — any amount withheld counts as a taxable distribution and may trigger penalties if under 59½.
4. Open a Roth IRA if needed. Fidelity, Schwab, and Vanguard all handle same-institution and cross-institution rollovers. The Roth IRA does not need to be at the same custodian as the solo 401(k).
5. Pay taxes from outside funds. Set aside the tax payment from a taxable brokerage or savings account. Taxes withheld from the conversion itself reduce the Roth IRA balance and eliminate that capital's future tax-free compounding.
6. Report on Form 1040. Your plan issues Form 1099-R in January showing the distribution. Report the taxable amount on Form 1040 line 5b. If you have no IRA basis, Form 8606 is not required for this transaction — the entire solo 401(k) rollout is reportable directly on the 1040.
7. Repeat annually. A 7–12 year plan at $50K–$90K/year typically converts a $500K–$700K balance while keeping the annual effective rate at 17–22%.

Common mistakes

• Taking a check instead of requesting a direct transfer. If the plan issues a check payable to you, 20% is withheld by default. You must deposit 100% of the original balance (including the withheld 20% from other funds) into the Roth IRA within 60 days — or the withheld amount is a taxable distribution.
• Converting too much in one year. Rolling $500K at once pushes most of it into the 32–37% brackets. A 10-year plan at 17–22% beats a one-year plan at 32% even accounting for time value of the tax deferral.
• Forgetting IRMAA's two-year lookback. A large 2026 conversion affects 2028 Medicare Part B premiums. Model two years ahead, not just this year's bracket.
• Terminating the plan at peak income. Final-year consulting projects can push income to its highest point. Terminating the plan that year means converting at the highest bracket of the wind-down. Wait a year if income is expected to drop significantly.
• Confusing the Rule of 55. IRC § 72(t)(2)(A)(v) allows penalty-free withdrawals from a 401(k) if you separate from service at 55 or older. This applies to the solo 401(k) — if you shut down your business at 57, you can take penalty-free solo 401(k) distributions (and roll to Roth, paying only income tax). The Rule of 55 does NOT apply to IRAs, so the penalty disappears at 59½ regardless of the account type.

Talk to a Roth conversion specialist

A solo 401(k) conversion strategy intersects business exit timing, Medicare enrollment, Social Security delay decisions, and 10–15 years of tax projections. A fee-only financial advisor who specializes in Roth conversion strategy — not a generalist, not someone who earns commissions on products — can build the year-by-year model that shows the exact conversion amount for each phase of your wind-down.

RothConversionAdvisorMatch is a referral service, not a licensed advisory firm. We may receive compensation from professionals in our network. Content is for informational purposes only and does not constitute financial, tax, or legal advice.

Values verified as of June 2026 against IRS Rev. Proc. 2025-32, IRS Notice 2025-67, CMS 2026 IRMAA fact sheet, and SECURE 2.0 Act of 2022.

1. IRS Notice 2014-54 and IRC § 3405(c) — withholding rules for 401(k) distributions; direct rollover rules. irs.gov/pub/irs-drop/n-14-54.pdf
2. SECURE 2.0 Act of 2022, § 109 — super catch-up for ages 60–63; IRS Notice 2025-67 — 2026 retirement plan limits: employee deferral $24,500, catch-up 50+ $8,000, super catch-up 60–63 $11,250 additional ($35,750 total), §415 total $72,000. irs.gov/pub/irs-drop/n-25-67.pdf
3. CMS 2026 Medicare costs — IRMAA Tier 1 threshold $109,000 single / $218,000 MFJ MAGI; Part B base premium $202.90/month. cms.gov
4. IRS Rev. Proc. 2025-32 — 2026 federal income tax brackets ($50,400 top of 12% bracket single; $105,700 top of 22% bracket single), standard deductions ($16,100 single, $32,200 MFJ), age 65+ additional deduction ($2,050 single, $1,650 MFJ per person). irs.gov/pub/irs-drop/rp-25-32.pdf