SEP IRA vs Solo 401(k): Which Is Better for the Self-Employed

The short answer

If you’re a sole proprietor or single-member LLC with no employees and you want retirement savings without much paperwork, a SEP IRA is the simpler choice. If you want to save more per dollar of income — especially at modest income levels — or you want a Roth option and the ability to borrow against your balance, a Solo 401(k) usually wins. Both are built for the same person — someone who works for themselves — but they get you to the contribution ceiling through very different math, and that math matters most if your net self-employment income is under roughly $150,000 a year.

Why the two plans behave so differently

Both a SEP IRA and a Solo 401(k) let a self-employed person stash away pre-tax (or in the 401(k)’s case, sometimes Roth) dollars for retirement, and both can reach the same overall annual limit — $72,000 for 2026, up from $70,000 for 2025. But they get there through completely different mechanisms.

SEP IRA: one lever, pulled hard

A SEP IRA only has an “employer contribution.” Even though you’re self-employed, the IRS treats your contribution as if your business is contributing on your own behalf. The limit is 25% of your compensation — but for a sole proprietor, “compensation” is net self-employment income after you’ve subtracted the deduction for one-half of your self-employment tax, and after you back out the contribution itself. Run through the actual worksheet in IRS Publication 560 and the real cap works out to about 18.6%–20% of your net profit, not a clean 25%. There’s no separate “employee” contribution, no catch-up for turning 50, and, in practice, no Roth version — Section 601 of SECURE 2.0 has permitted Roth SEP contributions since 2023, but few custodians actually offer them, so most SEP IRAs are pre-tax only.

Solo 401(k): two levers, stacked

A Solo 401(k) — sometimes called a one-participant 401(k) — lets you wear two hats. As the “employee,” you can defer up to $24,500 for 2026 (up from $23,500 for 2025) regardless of how little you earned, as long as you earned at least that much. As the “employer,” you can then add a profit-sharing contribution of up to 25% of compensation, calculated the same way as the SEP. The two layers stack, up to the same overall $72,000 ceiling (plus catch-up contributions if you’re 50 or older — $8,000 for 2026, with an enhanced $11,250 catch-up for savers age 60–63 under SECURE 2.0 rules). This is why a Solo 401(k) almost always lets a modest earner contribute more than a SEP IRA would, dollar for dollar.

Here’s the concrete version: if you net $60,000 in self-employment income after expenses, a SEP IRA caps you at roughly $11,000–$12,000. A Solo 401(k) lets you defer $24,500 as “employee” first, then add the employer share on top — potentially doubling what you can put away in the same year, on the same income.

The side-by-side comparison

Figures above are for 2026 and are adjusted for inflation every year. Always confirm the exact current-year numbers at IRS.gov before you contribute, since over- or under-contributing has real tax consequences.

Which one actually fits your situation

The freelance graphic designer with a side income. Say you net $25,000 a year from freelance work on top of a day job with its own 401(k). You don’t want paperwork, and the dollar amounts involved are modest either way. A SEP IRA, opened in an afternoon at a brokerage with no annual filing requirement, does the job without friction.

The solo consultant netting $70,000–$90,000 with no employees. This is the classic case for a Solo 401(k). The employee deferral piece alone — $24,500 — eats up roughly a quarter to a third of net income before the 25% employer layer even kicks in. A SEP IRA caps out noticeably lower on the same income. If this person also wants some of their savings in Roth form, most SEP custodians still don’t offer the Roth SEP option that SECURE 2.0 authorized; the Solo 401(k) can, if the plan allows Roth deferrals.

The business owner who plans to hire within a year or two. A SEP IRA is forgiving here — if you bring on employees who meet the eligibility rules (generally age 21+, three years of service in the last five, and $800 or more in compensation for 2026, per IRS rules), you simply extend SEP coverage to them at the same contribution percentage. A Solo 401(k), by contrast, is built around having zero employees; hiring someone who isn’t your spouse generally means replacing the plan with a standard 401(k), which comes with more administration and nondiscrimination testing.

The high earner near 50 who wants to catch up fast. A Solo 401(k)’s catch-up contributions — and the newer, larger catch-up for ages 60–63 under SECURE 2.0 — aren’t available in a SEP IRA at all. If you’re playing catch-up on retirement savings in your later self-employed years, the 401(k) structure gives you more room.

The person who wants to borrow against retirement savings in an emergency. Only the Solo 401(k) allows loans. A SEP IRA, like any IRA, does not permit loans — taking money out early means taxes and, generally, a 10% early withdrawal penalty if you’re under 59½.

The trap people fall into when moving between them

The most common mistake isn’t picking the wrong plan — it’s picking a Solo 401(k) and then hiring an employee without realizing what that triggers. The “solo” in Solo 401(k) is not a marketing term; it’s a legal condition. The moment you have a common-law employee (other than your spouse) who works enough hours to become eligible, your one-participant plan generally needs to be converted or replaced, often with the help of a third-party administrator, because it’s no longer exempt from the broader 401(k) nondiscrimination and reporting rules. Business owners who scale up quickly sometimes discover this mid-year, after contributions have already been made under the old plan.

The reverse trap happens with SEP IRAs: people assume they can switch from SEP to Solo 401(k) retroactively to “catch up” contribution room for a year that’s already closed. In most cases you can’t. The IRS treats these as distinct plan types, and contribution elections for 401(k) employee deferrals in particular depend on timely payroll-style deferral elections during the plan year — in most cases you can’t reach back into a completed tax year and decide, after the fact, that you wish you’d deferred as an employee. The one exception is Section 317 of SECURE 2.0: a sole proprietor or single-member LLC with no employees that is adopting its first-ever 401(k) can establish the plan and make retroactive employee deferrals for the prior year up to its tax filing deadline, without extensions.

The safest approach is to decide before year-end, based on your actual or projected net self-employment income, rather than switching plan types reactively once you see how a given year turned out. If your income fluctuates wildly year to year, a Solo 401(k) is flexible enough to let you dial the employee deferral up or down, while the employer contribution stays optional — so it can flex with a good year or a lean one in ways a SEP IRA, which has only the one 25% lever, cannot.

Sources

• IRS — One-Participant 401(k) Plans: https://www.irs.gov/retirement-plans/one-participant-401k-plans
• IRS — Simplified Employee Pension Plan (SEP): https://www.irs.gov/retirement-plans/plan-sponsor/simplified-employee-pension-plan-sep
• IRS — Retirement Topics: 401(k) and Profit-Sharing Plan Contribution Limits: https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-topics-401k-and-profit-sharing-plan-contribution-limits
• IRS Publication 560, Retirement Plans for Small Business: https://www.irs.gov/publications/p560

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