SEP-IRA vs Solo 401(k) for Self-Employed (2026): Contribution Limits, Roth Option, and Worked Examples

For self-employed individuals and small-business owners with no full-time non-spouse employees, the two best retirement-account options are the SEP-IRA and the one-participant ("Solo") 401(k). Both are governed by IRS Publication 560 (Retirement Plans for Small Business). Both allow tax-deductible contributions far above the $7,000 traditional-IRA limit (or $8,000 with the age-50 catch-up). Both produce identical maximum contributions at very high income levels. But for self-employed workers earning under approximately $230,000 of net earnings from self-employment, the Solo 401(k) typically permits substantially larger contributions — and offers a Roth option that the SEP-IRA does not.

This guide compares the two for 2026 using the inflation-adjusted figures from Rev. Proc. 2025-32 and IRS Notice 2025-67. Worked examples at $30,000, $90,000, and $300,000 self-employment income show exactly where the Solo 401(k) advantage starts and where the two plans converge.

2026 Limits Side-by-Side

The Math: Why Solo 401(k) Wins at Most Income Levels

Self-employed net earnings from self-employment (NESE) is gross income from the business minus business expenses minus one-half of self-employment tax (the deductible portion). For Solo 401(k) and SEP-IRA profit-share calculations, the IRS uses NESE further reduced by the retirement contribution itself, producing the well-known "20% effective rate" for self-employed (versus 25% for W-2 compensation).

Per IRS Publication 560, the calculation is:

Adjusted SE Earnings = (Schedule C net profit) − (1/2 of SE tax)

Maximum profit-share contribution = Adjusted SE Earnings × 0.2 (the 20% effective rate)

The Solo 401(k) adds the employee deferral on top. The deferral is dollar-for-dollar of compensation up to the $23,500 limit (2026), so a self-employed person with $40,000 net SE income can defer the full $23,500 plus add the 20% profit-share.

Worked Example #1 — $30,000 Self-Employment Income

Worked Example #2 — $90,000 Self-Employment Income

Worked Example #3 — $300,000 Self-Employment Income

The SECURE 2.0 Catch-Up Changes for 2026

The SECURE 2.0 Act of 2022 introduced two changes that affect Solo 401(k) catch-up calculations in 2026:

• Age 60-63 super catch-up. Participants who attain age 60, 61, 62, or 63 during 2026 can make a catch-up contribution of the greater of $10,000 or 150% of the regular catch-up — so $7,500 × 150% = $11,250 in 2026. The super catch-up reverts to the regular age-50 catch-up starting the year the participant attains age 64.
• Mandatory Roth catch-up over $145,000. Participants whose prior-year FICA wages from the same employer exceeded $145,000 (2026 figure pending Treasury guidance; trailing 2024 indexed figure was $145,000) must make their catch-up contributions on a Roth basis. The mandatory Roth catch-up requirement was deferred to plan years beginning 2026 per IRS Notice 2023-62. Self-employed individuals receiving K-1 or Schedule C income rather than W-2 wages from the plan-sponsoring entity may have a different application of the rule — verify with a qualified retirement plan administrator.

The Roth Option — Solo 401(k) Only

The SEP-IRA has no Roth equivalent. Contributions to a SEP-IRA are pre-tax only, and the account grows tax-deferred until withdrawal. SECURE 2.0 §601 added Roth treatment to employer contributions in 401(k) and similar plans, but Treasury and IRS implementing guidance for self-employed Solo 401(k) Roth profit-sharing is still developing as of May 2026. Confirm with your plan custodian whether they support Roth profit-sharing and whether your plan document was amended to permit it.

For Solo 401(k) employee deferrals, the Roth option has been available since 2006. Roth deferrals are after-tax — meaning no current-year deduction — but the account grows tax-free and qualified withdrawals (after age 59½ and 5-year holding) are entirely tax-free. There are no income limits on Roth Solo 401(k) deferrals, unlike the Roth IRA (which phases out for single filers at $165,000-$180,000 in 2026).

Deadlines and Plan Establishment

This is one of the more frequent sources of self-employed retirement-planning errors.

• SEP-IRA can be both established and funded by the tax return due date including extensions. A sole proprietor who files an extension to October 15, 2027 has until that date to open and fund a 2026 SEP-IRA with a custodian. The IRS Form 5305-SEP (or a custodian-specific equivalent) is the plan document.
• Solo 401(k) employee deferrals generally must be made through a plan that existed as of December 31, 2026. SECURE Act §201 (2019) eased the rule slightly — a Solo 401(k) for the employer-contribution side can be established by the tax return due date including extensions (October 15, 2027 for 2026). But the employee-deferral side still requires the plan to have existed by December 31, 2026, and the deferral election to have been made before year-end. Self-employed individuals discovering Solo 401(k) eligibility in March 2027 typically cannot make a 2026 deferral, only a 2026 employer profit-share contribution.

The "No Full-Time Employees" Rule

Solo 401(k) is available only to self-employed individuals and small-business owners with no full-time non-spouse employees. The IRS definition of "full-time" depends on the plan document but typically follows the standard ERISA definition: 1,000+ hours per year, or under the long-term part-time worker rule from SECURE 2.0 §125, 500+ hours for 2 consecutive years (for plan years beginning 2025 and later). A working spouse can be covered by the same Solo 401(k); they make their own employee deferral and the business can make a separate employer profit-share for the spouse.

The moment a non-spouse employee crosses the eligibility threshold, the plan is no longer a "one-participant" plan and the employer must either expand it to a full 401(k) (with non-discrimination testing and Form 5500 filing) or terminate it. SEP-IRA, by contrast, must cover all employees who meet the plan-document eligibility rules (typically age 21, worked for the employer in 3 of the prior 5 years, and earned at least $750 in 2026 per IRS Publication 560). This is why SEP-IRA is often the wrong choice once you hire your first employee.

Loans — Solo 401(k) Advantage

Solo 401(k) plans typically permit loans of up to 50% of vested balance or $50,000 (whichever is less). The loan must be repaid generally over 5 years (longer for principal residence purchase) at a market interest rate. SEP-IRAs do not permit loans — any "loan" from an IRA is a prohibited transaction under IRC §4975 and disqualifies the entire IRA, triggering immediate taxation of the full balance.

Roth Conversions and Backdoor Strategies

SEP-IRA balances complicate the "backdoor Roth IRA" strategy because of the IRA pro-rata rule under IRC §408(d)(2). Any pre-tax balance in any traditional IRA (including SEP-IRA, SIMPLE-IRA, rollover IRA) creates a pro-rata fraction that taxes a portion of any Roth conversion. Solo 401(k) balances are not aggregated for the pro-rata rule — they exist outside the IRA universe. Self-employed individuals who plan to use the backdoor Roth IRA each year are usually better off with a Solo 401(k) than a SEP-IRA for that reason alone.

When SEP-IRA Still Makes Sense

Despite the Solo 401(k)'s advantages in most scenarios, SEP-IRA is still preferred when:

• You discover retirement-saving capacity after year-end. A SEP-IRA can be established and funded by the tax-return extension deadline. Solo 401(k) employee deferrals are locked out after December 31.
• You hate paperwork. SEP-IRA opens at any IRA custodian in 15 minutes. No annual Form 5500-EZ ever required (no asset threshold). No mandatory plan document review. No vesting schedules.
• You expect to hire full-time employees soon. SEP-IRA can cover employees more easily than transitioning a Solo 401(k) to a full 401(k).
• Your business income is so high that the cap binds anyway. Above approximately $231,000 of net SE income, the 25%-of-comp profit-share alone reaches the $70,000 annual additions cap and the deferral provides no incremental benefit.
• You don't need the Roth option. Some taxpayers in low brackets actually prefer pre-tax for current deduction value and accept tax-deferred growth.

Comparison with Other Self-Employed Plans

Frequently Asked Questions