In the SEP IRA vs Solo 401k decision for 2026, a Solo 401(k) usually lets a self-employed person contribute more at low-to-mid income because it stacks a flat $24,500 employee deferral on top of the same profit-sharing math, while a SEP IRA wins on simplicity and a later funding deadline. Which one fits depends heavily on your business entity and how much you want to save.
Both plans share a $72,000 combined 2026 contribution ceiling (Source: IRS Notice 2025-67). The Solo 401(k) adds a $24,500 employee deferral (plus catch-up for age 50+), so it typically allows a larger contribution below roughly $288,000 of income. The SEP IRA offers no employee deferral, no loans, and lighter paperwork, and it can be opened and funded up to the tax deadline plus extensions.
SEP IRA vs Solo 401k: the short answer
For most solo business owners in 2026, a Solo 401(k) allows a larger contribution at the same income because it combines two contribution sources: a fixed employee salary deferral and an employer profit-sharing amount. A SEP IRA offers only the employer piece. Both plans cap total contributions at $72,000 in 2026 (Source: IRS Notice 2025-67).
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The tradeoff is administrative. A SEP IRA is often described as one of the simplest employer plans to open and maintain, with no annual IRS filing in most years. A Solo 401(k) may permit larger contributions, Roth deferrals, and participant loans, but it carries more paperwork, including a Form 5500-EZ once plan assets exceed $250,000 (Source: IRS, Form 5500-EZ instructions).
Because the numbers below use current-year figures, they may change annually with cost-of-living adjustments. For a deeper look at the deferral and profit-sharing math on a single plan, see the Q3 Advisors guide to Solo 401(k) contribution limits for 2026 and the broader 2026 retirement contribution limits.
At-a-glance comparison table (2026)
This table summarizes the core differences self-employed savers weigh when choosing between a SEP IRA and a Solo 401(k) for 2026. Every dollar figure is a 2026 amount from IRS Notice 2025-67 unless noted. Individual eligibility and outcomes depend on entity type, income, and the plan document a provider offers.
| Feature (2026) | SEP IRA | Solo 401(k) |
|---|---|---|
| Who contributes | Employer only | You wear “both hats”: employee and employer |
| Employee salary deferral | None (post-1996 SEPs allow no elective deferrals) | Up to $24,500 |
| Employer / profit-sharing | Up to 25% of compensation (~20% of net earnings for sole proprietors) | Up to 25% of compensation (~20% for sole proprietors) |
| Combined limit (415(c)) | $72,000 | $72,000 (excludes catch-up) |
| Catch-up, age 50+ | Generally none | +$8,000 |
| Enhanced catch-up, age 60-63 | Generally none | +$11,250 (if plan permits) |
| Practical max, age 50+ | Up to $72,000 | Up to ~$80,000 |
| Practical max, age 60-63 | Up to $72,000 | Up to ~$83,250 |
| Compensation cap | $360,000 | $360,000 |
| Roth option | Roth designation only if provider offers it (post-SECURE 2.0) | Designated Roth employee deferrals if plan permits |
| Participant loans | No | Yes, if the plan allows (lesser of $50,000 or 50% of vested balance) |
| Employees allowed | Yes (must fund the same % for all eligible) | Owner and spouse only |
| Annual IRS filing | None in most years | Form 5500-EZ once assets exceed $250,000 |
| Setup / funding deadline | Tax-filing deadline plus extensions | Plan generally established by year-end (see deadlines below) |
What is a SEP IRA?
A SEP IRA (Simplified Employee Pension) is an employer-funded retirement account that a self-employed person or small business can open with minimal paperwork. Only the employer contributes; there is no employee salary deferral. For 2026, the contribution is limited to the lesser of 25% of compensation or $72,000 (Source: IRS Notice 2025-67; IRS Publication 560).
For a sole proprietor or single-member LLC, the effective ceiling is lower than the headline 25%. Because the calculation runs on net earnings from self-employment (net profit reduced by half of self-employment tax and by the contribution itself), the practical rate works out to about 20% of net earnings (Source: IRS Publication 560). The compensation cap for 2026 is $360,000 (Source: IRS Notice 2025-67).
A SEP IRA can cover employees, but that is a feature and a cost: an employer generally must contribute the same percentage of compensation for every eligible employee. That uniform-percentage rule is why a SEP can become expensive for a business that adds staff.
What is a Solo 401(k)?
A Solo 401(k), also called a one-participant 401(k) or owner-only 401(k), is a 401(k) plan for a business with no employees other than the owner and a spouse. The owner contributes in two capacities: as an employee making salary deferrals, and as the employer making profit-sharing contributions (Source: IRS, one-participant 401(k) plans).
For 2026, the employee deferral limit is $24,500 (Source: IRS Notice 2025-67). On top of that, the employer profit-sharing piece is limited to 25% of compensation (about 20% of net earnings for sole proprietors), and the sum of both, excluding catch-up, cannot exceed $72,000 (Source: IRS Notice 2025-67; IRS Publication 560).
Savers age 50 and older may add an $8,000 catch-up in 2026, and those age 60 to 63 may add an enhanced $11,250 catch-up under SECURE 2.0, if the plan document permits it (Source: IRS Notice 2025-67). Those catch-up amounts sit above the $72,000 cap, which is why the practical Solo 401(k) maximum can reach roughly $80,000 (age 50+) or $83,250 (age 60-63).
2026 contribution limits side by side
The single biggest driver in the SEP IRA vs Solo 401k choice is the flat employee deferral. Both plans use the same $72,000 combined cap and the same ~20% self-employed profit-sharing rate, so the Solo 401(k)’s $24,500 deferral is the extra layer that lets many owners save more at the same income (Source: IRS Notice 2025-67).
| 2026 limit | Amount | Source |
|---|---|---|
| Employee deferral (Solo 401k) | $24,500 | IRS Notice 2025-67 (IRC 402(g)(1)) |
| Combined annual additions cap (both plans) | $72,000 | IRS Notice 2025-67 (IRC 415(c)(1)(A)) |
| Catch-up, age 50+ | $8,000 | IRS Notice 2025-67 (IRC 414(v)(2)(B)(i)) |
| Enhanced catch-up, age 60-63 | $11,250 | IRS Notice 2025-67 (IRC 414(v)(2)(E)(i)) |
| Compensation cap | $360,000 | IRS Notice 2025-67 (IRC 401(a)(17), 408(k)(3)(C)) |
| SEP minimum comp to require a contribution | $800 | IRS Notice 2025-67 (IRC 408(k)(2)(C)) |
One common misconception is that a Solo 401(k) permits $24,500 plus $72,000. It does not. The correct reading is that employee deferrals and employer profit-sharing together cannot exceed $72,000 in 2026, with catch-up contributions layered above that ceiling (Source: IRS Notice 2025-67; IRS Publication 560).
The math that changes the answer: your business entity
Your entity type quietly changes the winner, and most comparison pages skip it. The 25% profit-sharing rate applies cleanly to W-2 wages, so an S-corporation owner-employee gets a true 25% of W-2 compensation. A sole proprietor or single-member LLC instead uses net earnings from self-employment, which drops the effective rate to about 20% (Source: IRS Publication 560).
This matters because both a SEP IRA and the employer side of a Solo 401(k) use the same net-earnings base for a sole proprietor. The percentage is identical between the two plans. What differs is that the Solo 401(k) adds the flat $24,500 employee deferral on top, which the SEP IRA cannot match (Source: IRS Notice 2025-67).
For S-corporation owners, the profit-sharing contribution is calculated on W-2 wages, not distributions. A lower salary can shrink the amount either plan permits, so the interaction between compensation strategy and retirement savings is worth modeling before choosing. Owners weighing salary levels may also want to consider how contributions interact with the Net Investment Income Tax for 2026.
Income-based contribution examples (sole proprietor, 2026)
These worked examples show why a Solo 401(k) often allows more at lower incomes. Each row assumes a sole proprietor (not an S-corp), uses 2026 limits, and applies the ~20% self-employed profit-sharing rate on net earnings after the standard half-of-SE-tax adjustment. Figures are illustrative and rounded; your own result depends on exact net earnings and self-employment tax (Source: IRS Publication 560; IRS Notice 2025-67).
| Net business profit | SEP IRA (employer only) | Solo 401(k) (deferral + employer) | Solo 401(k) advantage |
|---|---|---|---|
| $50,000 | ~$9,300 | ~$33,800 | ~$24,500 |
| $100,000 | ~$18,600 | ~$43,100 | ~$24,500 |
| $150,000 | ~$27,900 | ~$52,400 | ~$24,500 |
| $200,000 | ~$37,200 | ~$61,700 | ~$24,500 |
| ~$288,000+ | Approaches $72,000 | Approaches $72,000 | Roughly equal |
The pattern is consistent: below the break-even zone, the Solo 401(k) allows about $24,500 more (before any catch-up) because of the employee deferral. As income rises toward roughly $288,000 and above, the employer profit-sharing amount alone approaches the $72,000 cap under both plans, so the two converge (Source: IRS Notice 2025-67). The ~$288,000 break-even is an approximation and shifts with self-employment tax mechanics.
Roth options: a real difference
A Solo 401(k) can accept designated Roth employee deferrals if the plan document offers them, letting an owner contribute after-tax dollars that grow tax-free (Source: IRS, designated Roth accounts guidance). A traditional SEP IRA historically allowed pre-tax employer contributions only, though SECURE 2.0 created a Roth SEP option that some providers now support (Source: IRS Publication 560).
In practice, the Roth SEP option remains uncommon at many custodians, so an owner who wants a straightforward Roth path within a self-employed plan often finds it easier inside a Solo 401(k). Roth availability always depends on what the specific provider’s plan document permits.
Some Solo 401(k) plans also permit voluntary after-tax contributions and in-plan conversions, an approach sometimes called a mega backdoor Roth. This strategy is only available where the plan document explicitly allows after-tax contributions and conversions, and the rules can be technical. Owners exploring Roth strategy may also review the Q3 Advisors Roth conversion service and the 2026 Roth conversion statistics.
Loans, deadlines, and paperwork
Three practical mechanics separate the plans beyond raw contribution room: participant loans, setup deadlines, and annual filing. A Solo 401(k) may permit a participant loan of the lesser of $50,000 or 50% of the vested balance, if the plan allows it, while a SEP IRA never permits loans because IRA rules prohibit them (Source: IRS, retirement plan loan FAQs; IRS Publication 560).
Setup and funding deadlines
Setup and funding deadlines differ between the two plans. A SEP IRA can be established and funded up to the business’s tax-filing deadline plus extensions (Source: IRS Publication 560). A Solo 401(k) generally must be established by year-end, though SECURE 2.0 lets a sole proprietor treat a plan adopted by the tax deadline as effective for the prior year for employer contributions (Source: IRS, SECURE 2.0 guidance).
The distinction is decision-critical for someone reading this in the spring after year-end. If the prior year has already closed and no plan existed, a SEP IRA is often the only way to still make a prior-year contribution.
Administrative burden and filings
A SEP IRA typically requires no annual IRS filing. A Solo 401(k) requires a Form 5500-EZ once total plan assets exceed $250,000 at year-end, and a final 5500-EZ when the plan terminates (Source: IRS, Form 5500-EZ instructions). Neither plan is complex compared with a plan covering employees, but the SEP carries the lighter ongoing load.
Can you have both, and can you roll a SEP into a Solo 401(k)?
Yes, a business owner can have both a SEP IRA and a Solo 401(k), but the $72,000 combined annual additions limit generally applies across plans of the same employer, so the accounts do not multiply the ceiling (Source: IRS Notice 2025-67; IRS Publication 560). Many owners open both only during a transition year.
Rolling a SEP IRA into a Solo 401(k) is generally permitted, because pre-tax SEP IRA assets can typically be rolled into a 401(k) plan that accepts rollovers (Source: IRS, rollover guidance). A common sequence looks like this:
- Confirm the Solo 401(k) plan document accepts incoming rollovers.
- Request a direct rollover (trustee-to-trustee) from the SEP IRA custodian to avoid withholding.
- Deposit the pre-tax SEP balance into the Solo 401(k) rollover source.
- Keep records showing the rollover was direct, so it is not treated as a distribution.
Whether this move helps depends on your goals. Consolidating into a Solo 401(k) can enable loans and, for some owners, cleaner backdoor Roth mechanics by removing pre-tax IRA balances from the pro-rata calculation. The tax treatment of rollovers can be technical and depends on account types.
When to choose each plan
Choose based on your priority: maximum savings and flexibility point toward a Solo 401(k), while simplicity and a later deadline point toward a SEP IRA. The right answer depends on income, entity type, whether you have or plan to hire employees, and how much administrative work you are willing to carry (Source: IRS Publication 560).
| Your situation | Often points toward |
|---|---|
| Want to contribute the most at low-to-mid income | Solo 401(k) |
| Want Roth deferrals or a participant loan | Solo 401(k) |
| Value minimal paperwork and no annual filing | SEP IRA |
| Missed year-end and need a prior-year contribution | SEP IRA |
| Have variable income and want flexibility to skip years | SEP IRA |
| Plan to hire non-spouse employees soon | SEP IRA (Solo 401k requires owner/spouse only) |
| Very high income (~$288k+), simplicity preferred | Either (contributions converge) |
Both plans require minimum distributions to begin at age 73 under current law, so RMD timing is not a differentiator between them (Source: IRS, required minimum distributions rules). For details, see the Q3 Advisors guide to required minimum distributions for 2026.
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Q3 Advisors is a registered investment adviser focused on retirement tax planning. This article is educational and is not advice; for guidance on your own circumstances, consult a qualified tax or financial professional.
Frequently asked questions
What are the disadvantages of a Solo 401(k)?
A Solo 401(k) carries more administration than a SEP IRA, including a Form 5500-EZ once plan assets exceed $250,000 (Source: IRS, Form 5500-EZ instructions). It generally must be established by year-end, and it cannot cover non-spouse employees. If a business hires staff, the plan usually must convert to a standard 401(k) or be replaced, adding cost and complexity.
Is a Solo 401(k) better than a SEP-IRA?
Neither is universally better. A Solo 401(k) often allows a larger 2026 contribution below roughly $288,000 of income because of its $24,500 employee deferral, plus Roth deferrals and loans (Source: IRS Notice 2025-67). A SEP IRA is simpler, has no annual filing in most years, and can be funded up to the extended tax deadline. The fit depends on income, entity type, and priorities.
How much can I contribute to a SEP-IRA as a self-employed individual?
For 2026, a SEP IRA contribution is limited to the lesser of 25% of compensation or $72,000 (Source: IRS Notice 2025-67). For a sole proprietor or single-member LLC, the effective ceiling is about 20% of net earnings from self-employment, because the calculation uses net profit reduced by half of self-employment tax and by the contribution itself (Source: IRS Publication 560).
What is the downside of a SEP-IRA?
A SEP IRA has no employee salary deferral, so at low-to-mid income it usually permits a smaller contribution than a Solo 401(k) (Source: IRS Notice 2025-67). It allows no participant loans and, traditionally, limited Roth access. If the business has eligible employees, the employer generally must contribute the same percentage of pay for each one, which can become costly.
Can you have both a SEP IRA and a Solo 401(k)?
Yes, an owner can maintain both, but the $72,000 combined annual additions limit for 2026 generally applies across plans of the same employer, so the two accounts do not double the ceiling (Source: IRS Notice 2025-67; IRS Publication 560). Owners often hold both only during a transition year while consolidating retirement assets.
Can I roll a SEP IRA into a Solo 401(k)?
Generally yes. Pre-tax SEP IRA assets can typically be rolled into a Solo 401(k) that accepts incoming rollovers (Source: IRS, rollover guidance). A direct trustee-to-trustee transfer avoids withholding and keeps the move from being treated as a taxable distribution. Consolidating can enable loans and, for some owners, simpler backdoor Roth mechanics by clearing pre-tax IRA balances.
What is the difference between a SEP plan and a 401(k) plan?
A SEP is funded by employer contributions only, with no employee salary deferral and no loans. A 401(k), including a Solo 401(k), lets participants make employee deferrals (up to $24,500 in 2026) plus employer contributions, and it may permit Roth deferrals and loans if the plan allows (Source: IRS Notice 2025-67; IRS one-participant 401(k) guidance). The 401(k) generally offers more features and more paperwork.
Which is better for a sole proprietor, SEP IRA or Solo 401(k)?
For a sole proprietor focused on saving the most, a Solo 401(k) often allows a larger 2026 contribution because the flat $24,500 deferral stacks on the same ~20% profit-sharing math a SEP uses (Source: IRS Notice 2025-67; IRS Publication 560). A sole proprietor who values simplicity or a later funding deadline may prefer a SEP IRA. Outcomes depend on income and individual circumstances.
Sources
IRS Notice 2025-67, 2026 Amounts Relating to Retirement Plans and IRAs: https://www.irs.gov/pub/irs-drop/n-25-67.pdf
IRS COLA Increases for Dollar Limitations on Benefits and Contributions: https://www.irs.gov/retirement-plans/cola-increases-for-dollar-limitations-on-benefits-and-contributions
IRS Newsroom IR-2025-111 (401(k) limit increases to $24,500 for 2026): https://www.irs.gov/newsroom/401k-limit-increases-to-24500-for-2026-ira-limit-increases-to-7500
IRS Publication 560, Retirement Plans for Small Business: https://www.irs.gov/publications/p560
IRS One-Participant 401(k) Plans: https://www.irs.gov/retirement-plans/one-participant-401k-plans
IRS Retirement Plan Loan FAQs: https://www.irs.gov/retirement-plans/retirement-plans-faqs-regarding-loans
IRS Designated Roth Accounts guidance: https://www.irs.gov/retirement-plans/retirement-plans-faqs-on-designated-roth-accounts
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Disclaimer
This article is provided by Q3 Advisors for educational and informational purposes only. It is not investment, tax, or legal advice, and it is not a recommendation to buy, hold, or sell any security or to adopt any specific plan or strategy. Tax and retirement-plan rules are complex and depend on your individual circumstances; consult a qualified tax or financial professional before acting. Figures cited reflect 2026 amounts from the sources named and may change. Q3 Advisors is a registered investment adviser; additional information is available in our Form ADV.
