Retirement planning
SEP IRA vs Solo 401(k): Which Is Better for the Self-Employed?
Both plans let self-employed people shelter up to $72,000 in 2026, but they work differently — in contribution deadlines, Roth options, catch-up contributions, and administrative complexity. Here's how to pick the right one for your situation.
7 min read · Published April 2026
Key Takeaways
- Both plans allow up to $72,000 in total contributions for 2026 — the contribution limit is the same. The difference is in how you get there and how much flexibility you have.
- The Solo 401(k) has a Roth option; the SEP-IRA does not. For owners who want tax-free growth on retirement contributions, only the Solo 401(k) delivers it.
- A Solo 401(k) must be established by December 31 of the tax year. A SEP-IRA can be opened and funded as late as the tax filing deadline, including extensions — giving you until October if you extend.
- Solo 401(k) owners age 50 and older can contribute an additional $8,000 in catch-up contributions in 2026, for a total of $80,000. SEP-IRAs have no catch-up provision.
Why the comparison matters
If you’re self-employed, you have access to retirement contribution limits that W-2 employees don’t come close to. A Solo 401(k) or SEP-IRA can shelter up to $72,000 in 2026 — significantly more than the $24,500 employee limit in a traditional 401(k). Both plans show up in the same conversations, and they’re both legitimate tools. The question is which one fits your income structure, your timeline, and how you want to take the money out eventually.
The maximum contribution limit is identical. Everything else is different.
How each plan builds to $72,000
The two plans use completely different contribution mechanics to reach the same cap.
A Solo 401(k) works in two layers. As an employee of your own business, you can defer up to $24,500 of your compensation into the plan (the standard 2026 employee limit, the same as in any 401(k)). Then, as the employer, your business can contribute an additional amount: up to 25% of your W-2 wages if you run an S-corp, or up to about 20% of net self-employment income if you’re a sole proprietor or single-member LLC. The two layers together are capped at $72,000.
A SEP-IRA has only one layer — the employer contribution. You contribute up to 25% of W-2 wages (for S-corp owners) or about 20% of net SE income (for sole props). There is no employee deferral. To reach $72,000 via a SEP-IRA, you need $288,000 in W-2 wages or net SE income.
At $150,000 net SE income, the Solo 401(k) shelters $54,500 — nearly double the SEP-IRA's $30,000 contribution. The employee deferral is the difference. To reach $54,500 via a SEP-IRA alone, you'd need $272,500 in qualifying income.
The four differences that actually matter
| SEP-IRA | Solo 401(k) | |
|---|---|---|
| 2026 max contribution | $72,000 | $72,000 |
| Employee deferral | No — employer side only | Yes — $24,500 |
| Roth option | No | Yes (Roth Solo 401(k)) |
| Catch-up contributions (age 50+) | None | $8,000 more, for $80,000 total |
| Establishment deadline | Tax filing deadline (incl. extensions) | December 31 of the tax year |
| Contribution deadline | Tax filing deadline (incl. extensions) | Tax filing deadline (incl. extensions) |
| Annual filing requirement | None | Form 5500-EZ once assets exceed $250k |
| Rollover / loan options | No loans from SEP-IRA | Loans allowed from Solo 401(k) |
| Setup complexity | Simple — open and contribute | Moderate — plan document required |
The Roth question
The Roth Solo 401(k) is the most underused retirement planning tool for self-employed high earners. With a traditional SEP-IRA or Solo 401(k), you get a deduction now and pay tax on withdrawals in retirement. With a Roth Solo 401(k), you get no deduction now but withdrawals in retirement are tax-free.
The Roth option is only available through the Solo 401(k). SEP-IRAs are always pre-tax. Roth IRA contributions phase out at $153,000 (single) and $242,000 (MFJ) for 2026 — which means many self-employed high earners cannot contribute to a Roth IRA directly. The Roth Solo 401(k) has no income limit. If you expect your tax rate to be higher in retirement than it is now, or if you want to leave tax-free assets to heirs, the Roth Solo 401(k) is the only self-employed plan that gets you there without the backdoor Roth workaround.
The SEP-IRA is simpler. The Solo 401(k) is more flexible. Neither is automatically better — it depends on your income level, your entity structure, and whether you want the Roth option.
The deadline gap
This is where the two plans diverge most practically for self-employed people who are behind on planning.
A SEP-IRA can be opened and fully funded as late as your tax filing deadline, including extensions. If you file an extension, you have until October 15 of the following year to open the account and make the full contribution. Many owners use this to reduce a tax bill after year-end, once they know what their income was.
A Solo 401(k) must be established by December 31 of the tax year. If you missed that window, you cannot set one up retroactively. Once established, you can make the actual contributions up to the filing deadline — but the plan must exist before the year closes. For owners who want to start a Solo 401(k) to cover the current tax year, the December 31 deadline is the one that matters.
Missing the Solo 401(k) establishment deadline
Which one to choose
A few straightforward rules for most situations:
- Choose a Solo 401(k) if: you are age 50 or older and want catch-up contributions; you want a Roth option; your income is below $288,000 and you want to shelter more than the SEP-IRA percentage allows; or you’re an S-corp owner whose salary-to-profit structure makes the employee deferral more advantageous.
- Choose a SEP-IRA if: you’re setting up a plan after December 31 and need the current tax year to count; you prefer minimal administration and no annual filings; or your income already exceeds $288,000 and the SEP-IRA percentage alone gets you to the $72,000 cap.
- Consider a defined benefit plan if: you have more income than either plan can shelter and you want to defer significantly more than $72,000. Defined benefit contributions can exceed $275,000 annually at certain ages and income levels — a separate analysis, but worth knowing exists.
Neither plan is permanently better. Some owners run a SEP-IRA for years and switch to a Solo 401(k) when the Roth option becomes relevant or when the catch-up contribution threshold approaches. Others establish a Solo 401(k) from day one to preserve flexibility. The right call depends on where you are now, not just the current year’s deduction.
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Frequently asked
Questions owners actually ask
- Which plan gives me a larger deduction?
- At high income levels, both plans cap at the same $72,000 total limit, so the maximum deduction is identical. The difference is in how you reach that limit. With a Solo 401(k), you contribute up to $24,500 as an employee deferral (regardless of income) plus up to 25% of W-2 wages or 20% of net self-employment income as the employer contribution. With a SEP-IRA, you contribute only the employer side — 25% of W-2 wages or about 20% of net SE income. At lower income levels, the Solo 401(k)'s employee deferral lets you shelter more.
- Can I have both a SEP-IRA and a Solo 401(k) in the same year?
- You can have both open, but you cannot double-count the same income for contributions to both. If you have a Solo 401(k), you generally cannot also make SEP-IRA contributions for the same self-employment income. The IRS rules require you to choose. However, if you have multiple businesses — one with a SEP-IRA and one with a Solo 401(k) — specific rules apply to how contributions are coordinated. This is worth confirming with a CPA before doing it.
- I'm an S-corp owner paying myself a salary. Which plan works better?
- The Solo 401(k) generally works better for S-corp owners. As an S-corp owner with W-2 wages, you can make the full $24,500 employee deferral from your salary, plus the employer contribution of up to 25% of W-2 wages. The SEP-IRA limits your contribution to 25% of W-2 wages — there's no employee deferral component. At the same salary, the Solo 401(k) gets you to the $72,000 cap faster and with a lower required salary.
- What's the deadline to open a Solo 401(k)?
- The plan must be established by December 31 of the tax year for which you want to make contributions. This is a hard deadline — you cannot set up a Solo 401(k) in April and retroactively contribute for the prior year. Once the plan is established by year-end, you can make the actual contributions up to the tax filing deadline (including extensions — usually October 15 for individuals). The establishment deadline is the critical one to hit.
- Does a Solo 401(k) require a lot of paperwork?
- More than a SEP-IRA, but not dramatically so. Most financial institutions (Fidelity, Vanguard, Schwab) offer prototype Solo 401(k) plans with minimal setup paperwork. Once established, you file Form 5500-EZ annually once plan assets exceed $250,000. A SEP-IRA requires no annual filings — you contribute and the custodian handles the rest. If you're close to $250,000 in plan assets, factor in that the Solo 401(k) adds one annual form.
- Can I convert a SEP-IRA to a Solo 401(k)?
- You can't convert a SEP-IRA to a Solo 401(k) directly, but you can establish a Solo 401(k) for future contributions while leaving the existing SEP-IRA balance in place. Some Solo 401(k) plans also accept rollovers from SEP-IRAs, which would consolidate the accounts — check with your plan provider. Many owners make this switch when they want the Roth option or catch-up contributions and their income level makes the Solo 401(k)'s deferral structure more advantageous.
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Educational content only. This article is for informational purposes and does not constitute tax, legal, or financial advice. Every situation is different — consult a qualified professional before acting on anything here.