Roth SEP IRA vs. Roth Solo 401(k): 2026 Rules for Self-Employed Savers

What is the difference between a Roth SEP IRA and a Roth Solo 401(k)?

The names make the plans sound alike, but they are not two versions of one account. A regular SEP is funded through employer contributions. A one-participant 401(k), often called a Solo 401(k), lets an eligible owner contribute in two roles: employee and employer.

What are the 2026 contribution limits?

For a Solo 401(k), the general catch-up limit for an eligible participant age 50 or older is $8,000 in 2026. A higher $11,250 limit can apply in a year the participant turns 60, 61, 62, or 63. The plan must permit catch-up contributions.

How is a self-employed owner’s contribution calculated?

A sole proprietor or partner cannot use the employee percentage formula as though net business profit were W-2 pay. The IRS defines earned income for this purpose after subtracting the deductible part of self-employment tax and the contribution for the owner. That creates a circular calculation.

Use the worksheets in IRS Publication 560 or have the tax preparer and plan provider calculate the limit. An S corporation owner uses W-2 compensation for plan purposes, not shareholder distributions.

What does a Roth SEP IRA mean?

SECURE 2.0 allows a SEP arrangement to offer an election for contributions to go to a Roth IRA treated as a Roth SEP IRA. The employer does not have to offer the election. The employee must affirmatively elect Roth treatment before the contribution is made.

A Roth SEP contribution is included in the employee’s gross income. It does not turn the SEP into a salary-deferral plan, and it does not use the ordinary Roth IRA contribution limit or its income phaseouts.

What can the Roth feature in a Solo 401(k) cover?

A Solo 401(k) can accept designated Roth employee deferrals when the plan document permits them. Those deferrals are included in current taxable income. A qualified distribution from the designated Roth account can be tax-free when the applicable requirements are met.

Some plans may also permit Roth treatment for vested employer contributions, voluntary after-tax contributions, or in-plan Roth conversions. Those are separate features. They are not standard in every Solo 401(k).

How does the 2026 Roth catch-up rule affect a Solo 401(k)?

Beginning in 2026, a participant whose prior-year FICA wages from the employer sponsoring the plan exceeded $150,000 generally must make catch-up contributions on a Roth basis when the plan offers catch-ups. The threshold looks to wages from that plan sponsor, not total household income.

Entity type matters. A sole proprietor or partner may have self-employment income but no FICA wages from the sponsoring business. An S corporation owner may receive W-2 wages. Ask the plan administrator and tax professional how the final rules apply to the owner’s pay record.

How do employees change the choice?

A one-participant 401(k) is for a business owner with no common-law employees, or the owner and spouse. Hiring a worker who meets the plan’s eligibility terms can bring coverage, participation, testing, notice, and reporting duties that did not apply to an owner-only plan.

A SEP can include employees, but a contribution made for the owner generally requires a comparable contribution percentage for each eligible employee. That cost can be central when the business has workers or expects to hire.

Related businesses, leased workers, and independent-contractor classifications can affect who counts. Get plan counsel or a qualified administrator involved before excluding a worker from either arrangement.

What filing and recordkeeping duties apply?

A SEP is often easier to run, but it still needs a valid written arrangement, eligibility records, contribution calculations, employee notices, and correct tax reporting. The financial institution handles IRA account reporting, while the employer remains responsible for following the SEP terms.

A Solo 401(k) needs a signed plan document, timely elections, contribution records, separate trust or custodial accounting, and annual review. IRS one-participant 401(k) guidance generally requires Form 5500-EZ when total plan assets reach $250,000 or more at year-end. A final return can be required when the plan ends, even below that threshold.

Which provider questions should you ask before opening the plan?

• Does the SEP document and custodian accept Roth SEP contributions?
• Does the Solo 401(k) allow designated Roth employee deferrals?
• Are vested employer contributions allowed to receive Roth treatment?
• Are voluntary after-tax contributions supported in writing?
• Does the plan permit participant loans, if that feature matters?
• Who prepares or supports Form 5500-EZ?
• What are the setup, document, trading, account, and annual fees?
• What happens to the plan when the business hires an eligible employee?

When might each plan fit?

Neither plan wins for every business. Model the allowed contribution, current tax cost, employee cost, fees, filing work, and hiring plan before adopting one.

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