Solo 401(k) vs. Roth IRA: What’s the Difference — and Can You Have Both?

A solo 401(k) is a business retirement plan covering an owner, or the owner and a working spouse, without eligible common-law employees who must be covered. A Roth IRA is a personal retirement account. You can potentially use both: the plan has employee and employer contribution limits, while regular Traditional and Roth IRA contributions share their own annual limit.

In 2026, the solo plan's employee-plus-employer annual-additions ceiling is $72,000 before eligible catch-ups. The regular IRA ceiling is $7,500, or $8,600 at age 50 or older by year-end. Those numbers are upper limits—not a promise that your income supports the full deposit.

Solo 401(k) vs. Roth IRA at a glance

Sources: IRS Notice 2025-67, one-participant 401(k) guidance, Notice 2024-2, section L, and IRS RMD FAQs.

Two contribution roles—not two independent maximums

Think of the business owner as wearing two hats:

• Employee: the 2026 basic deferral ceiling is $24,500. It generally follows the person across 401(k), 403(b), SIMPLE and SARSEP arrangements; narrower plan-specific limits can apply. If a day-job 401(k) already receives $15,000, only $9,500 of that basic employee-deferral room remains—not another $24,500.
• Employer: the contribution is generally up to 25% of qualifying W-2 plan compensation, or an adjusted self-employed calculation commonly using a 20% reduced rate. Both sides must fit the annual-additions and compensation rules.

Eligible catch-ups sit outside the $72,000 annual-additions ceiling, giving potential totals of $80,000 at age 50+ or $83,250 at ages 60–63 in 2026. Compensation, personal deferral limits and plan terms still apply. For 2026, if your 2025 FICA wages (as defined in IRC §3121(a)) from the sponsoring employer exceeded $150,000, any catch-up contributions you choose to make generally must be Roth. Self-employment earnings alone are not those FICA wages. See the Roth 401(k) rules and T.D. 10033.

Several businesses do not automatically mean several employer limits. Related-employer aggregation can combine plans. An unrelated-employer plan may have a separate annual-additions limit, but the personal deferral ceiling remains shared. There is also a special rule combining a 403(b) with a qualified plan or SEP of a business you control by more than 50%. See Publication 571, chapter 3.

A working spouse can participate with their own qualifying compensation and personal limits. Marriage alone does not create business-plan compensation or double the owner's limit.

Can you also contribute to a Roth IRA?

Yes, if the personal IRA tests are met. Plan contributions do not directly consume the regular IRA limit. For a self-employed owner, however, the deductible part of self-employment tax and the deductible owner-plan contribution can reduce IRA compensation. Other regular Traditional or Roth IRA contributions use the same personal limit.

Direct Roth IRA eligibility depends on Roth MAGI, not gross business receipts. In 2026, the phase-out is $153,000–$168,000 for single/head-of-household filers and $242,000–$252,000 for married filing jointly/qualifying surviving spouses. Married filing separately generally uses $0–$10,000 when the spouses lived together at any time; living apart all year uses the single range. Publication 590-A explains the calculation, and our eligibility guide walks through the distinction.

A high MAGI does not impose that same cutoff on designated Roth deferrals inside a 401(k). That is a separate route, subject to the plan offering Roth and the applicable contribution limits—not a backdoor IRA conversion.

Does a solo 401(k) solve the backdoor Roth problem?

Sometimes it helps, but opening one is not enough. The owner's pro-rata IRA calculation generally includes traditional IRAs, traditional SEP IRAs and traditional SIMPLE IRAs, but excludes Roth IRA, Roth SEP and Roth SIMPLE balances. Inherited IRAs are generally separate unless a spouse treats one as their own. A 401(k) balance is outside that IRA pool.

The receiving plan must accept the exact eligible pre-tax IRA source. Nondeductible IRA basis cannot be rolled into a qualified plan; SIMPLE's two-year restriction may also apply. Calculate conversion tax using Form 8606, including relevant distributions, December 31 balances and outstanding rollovers. Do not assume “roll it over by year-end” is a complete rule or that the conversion will be tax-free. Use the Backdoor Roth Diagnostic to identify the records to check.

Access, tax and penalties are three different questions

A solo 401(k) is not simply locked until age 59½. Depending on the money source and plan terms, a permitted event can include severance from employment, disability, death, reaching 59½ or hardship. That does not mean every plan permits every distribution—or that a permitted withdrawal escapes income tax or the additional early-distribution tax. A hardship distribution is not automatically penalty-free.

Some plans permit loans, with statutory amount, repayment and other conditions. They are not an unrestricted withdrawal option, and an IRA cannot make participant loans. See the IRS distribution guide and Publication 560.

For a Roth IRA, the ordering rules put remaining regular contributions first, then conversions/rollovers, then earnings. Tax-free earnings are conditional: a qualified distribution requires the Roth IRA five-tax-year period plus age 59½, death, disability or the qualified first-home exception (subject to its lifetime limit). The account's name alone does not make every withdrawal tax-free. Read the withdrawal guide and Publication 590-B.

What administration should an owner expect?

• Solo plan: a written plan, contribution elections and records, document maintenance and applicable reporting. The usual Form 5500-EZ small-plan filing exception depends on combined assets of the employer's one-participant plans: when they exceed $250,000 at year-end, filing is generally required. A final plan year generally requires filing regardless of assets. See the Form 5500-EZ instructions.
• Employees: hiring an eligible common-law employee means the plan must address coverage and testing rules; the “solo” label does not override them. A person hired but not yet eligible is not the same as an eligible employee who must be covered.
• Roth IRA: no employer-plan Form 5500-EZ, but account paperwork, contribution deadlines, eligibility checks and basis/distribution records still matter. It is not “zero administration.”

Deadlines differ by contribution type, business structure and whether a plan is new. The first-year sole-proprietor exception is narrow, not a general permission to make late employee elections. Check the owner deadline checklist before relying on a business-return extension.

Which should you fund first?

There is no universal account order. Compare eligible compensation, employee obligations, available features and fees, current versus future tax treatment, access needs and your ability to administer the plan. A Roth IRA and a solo 401(k) can complement each other, but “Roth first” or “always maximize the bigger plan” skips those checks.

Start with the business-owner scorecard. For a different employer-funded arrangement, see SEP IRA vs. Roth IRA. An after-tax-plan-to-Roth strategy needs additional plan features and available annual-additions room; it is not an automatic $72,000 Roth allowance.