Both plans let a self-employed person stash up to $72,000 a year — but they take completely different paths to get there. The right choice depends on your income, Roth needs, and setup timing.
The SEP IRA and solo 401(k) are the two dominant retirement plan choices for self-employed individuals without full-time employees. They share the same annual contribution ceiling ($72,000 in 2026), but the mechanics are fundamentally different — and at most income levels below roughly $240,000 in net self-employment income, the solo 401(k) allows significantly higher contributions.
The reason is structural. A SEP IRA is employer-only contributions: you can put in up to 25% of net self-employment compensation, and that's it. A solo 401(k) has two separate contribution buckets: an employee deferral (up to $24,500 in 2026, regardless of income) plus an employer contribution (up to 25% of net SE compensation). The employee deferral is what gives the solo 401(k) its early advantage — at modest income levels, you can max the employee bucket even when the 25% employer contribution alone would be well below the limit.
Beyond the contribution math, the two plans differ in meaningful ways: Roth availability, loan access, administrative requirements, and setup deadlines. Understanding those differences makes the choice straightforward for most self-employed individuals.
| Feature | SEP IRA | Solo 401(k) |
|---|---|---|
| Who qualifies | Any self-employed or small-business owner | Self-employed with no full-time employees (spouse excepted) |
| 2026 employee deferral | None | $24,500 base; +$8,000 catch-up (ages 50–59 or 64+); +$11,250 (ages 60–63) |
| 2026 employer contribution | Up to 25% of net SE comp | Up to 25% of net SE comp |
| 2026 combined limit | $72,000 | $72,000 base; $80,000 (ages 50–59 or 64+); $83,250 (ages 60–63) |
| Roth option | No | Yes (at most custodians) |
| Loans | Not permitted | Permitted by IRS (up to 50% of vested, max $50,000) — but only if the plan document and custodian support it |
| After-tax / mega backdoor Roth | No | Yes, if plan document allows it |
| Setup deadline | Tax filing deadline + extensions (up to Oct 15) | December 31 of the tax year |
| Contribution deadline | Tax filing deadline + extensions | Employee deferral: Dec 31; employer: tax filing + extensions |
| IRS reporting | Minimal (Form 5498 from custodian) | Form 5500-EZ when plan assets exceed $250,000 |
| Administrative complexity | Very low — open an account, contribute | Low-moderate — plan document required; Form 5500-EZ above threshold |
| Employees allowed | Yes — must cover all eligible employees at same % of comp | No full-time employees other than spouse |
This is the core reason most self-employed individuals under ~$240,000 net income prefer the solo 401(k). At $60,000 of net SE income, the SEP IRA allows roughly $12,000 (~20% after the SE tax deduction). The solo 401(k) allows the same ~$12,000 as employer contributions plus up to $24,500 in employee deferrals — for a total closer to $36,500. That gap persists at every income level until the solo 401(k) hits its $72,000 combined ceiling — which happens around $240,000 of net SE income (when the employer portion reaches ~$47,500). Above ~$360,000, the SEP IRA's employer-only contributions also reach $72,000 and both plans are capped at the same amount.
A solo 401(k) lets you make two types of contributions in your role as both employee and employer of your own business. The employee deferral — up to $24,500 in 2026 — is a flat dollar limit that applies regardless of how much you earn. SECURE 2.0 added age-banded catch-ups on top: $8,000 additional for ages 50–59 or 64+, and $11,250 for ages 60–63. This means even a freelancer earning $40,000 can shelter $24,500 as an employee deferral and add employer contributions on top. The SEP IRA offers only the employer side, which at $40,000 of net income comes to roughly $8,000.
Unlike the SEP IRA — which is always pre-tax — most major custodians now offer a Roth designation for solo 401(k) employee deferrals. This means you can direct some or all of your $24,500 employee contribution into a Roth bucket, pay taxes now, and let it grow tax-free. There is no income limit on Roth solo 401(k) contributions (unlike Roth IRAs, which phase out above ~$165,000 for single filers in 2026). For high earners who want Roth exposure beyond what a backdoor Roth IRA can provide, the Roth solo 401(k) is a significant advantage.
The SEP IRA's biggest practical advantage is its setup deadline. You can open and fund a SEP IRA as late as your tax filing deadline including extensions — for a sole proprietor on extension, that's October 15 of the following year. If you're a freelancer or consultant who finalized your 2025 income in March 2026 and hasn't picked a retirement plan yet, a SEP IRA can still capture a large deduction for the prior year. The solo 401(k) must be established (plan documents signed) by December 31 of the tax year — contributions can come later, but the plan itself must exist.
The IRS allows solo 401(k) plans to include a loan provision — up to 50% of your vested balance, maximum $50,000, repayable over five years (longer for a primary home purchase). IRAs, including SEP IRAs, cannot offer loans at all. However, not all custodians support loans for individual 401(k)s. The plan document must explicitly allow them, and many low-cost or brokerage custodians simply don't offer the feature. If loan access is important to you, confirm with the custodian before opening the account — it's not a given. That said, loans carry real risks: they must be repaid on schedule, and a default is treated as a taxable distribution with potential penalties.
The SEP IRA is genuinely simple: open an account at any custodian, sign a brief IRS Form 5305-SEP or the custodian's equivalent adoption agreement, and contribute. No ongoing plan document, no annual filings, minimal record-keeping. The solo 401(k) requires a formal plan document (most custodians provide a prototype) and, once plan assets exceed $250,000 at year-end, annual filing of Form 5500-EZ. For most early-stage self-employed individuals the difference is minor — but if simplicity is your top priority, the SEP IRA has the edge.
The solo 401(k) hits its $72,000 combined ceiling around $240,000 of net SE income (when the employer portion reaches ~$47,500 plus the $24,500 deferral). The SEP IRA can't match that $72,000 until income reaches roughly $360,000, when employer-only contributions at 20% of net SE income also approach the cap. Below $360,000, the solo 401(k) either contributes more or contributes the same $72,000 while the SEP is still climbing — so the solo 401(k) leads at virtually every income level until both plans are maxed.
Technically you can hold both types of accounts, but you generally cannot contribute to both in the same year for the same self-employment activity. The IRS annual addition limit ($72,000 in 2026) applies per participant across all defined contribution plans maintained by the same employer. If you have a solo 401(k) through your freelance business, you cannot also make SEP IRA contributions for that same business in the same year. However, if you have a W-2 job at a separate employer with its own 401(k), the limits may be applied separately — this gets complicated, and a tax professional should review it before you act.
Yes — you can stop making SEP IRA contributions and open a solo 401(k) instead. Existing SEP IRA balances stay in the SEP IRA and can be rolled over to the solo 401(k) if the plan document allows it (most do). The key constraint is the solo 401(k) setup deadline: the plan must be established by December 31 of the first year you want to make 401(k) contributions. If you decide to switch in January, you're already too late for the prior year but on time for the current year — as long as you establish the plan before year-end.
Yes — a spouse who earns compensation from the business can participate as an employee. This effectively doubles the household contribution capacity, since both spouses get their own $24,500 employee deferral limit plus their share of employer contributions. The SEP IRA also covers a working spouse, but because neither spouse can make employee deferrals under a SEP, the solo 401(k) still has the higher potential limit when both spouses are contributing.
A solo 401(k) is only available when you have no full-time employees other than yourself and a spouse. If you hire a non-spouse employee who works 1,000+ hours in a year (traditional full-time threshold) or becomes eligible under the new long-term part-time rules (three consecutive years at 500+ hours), your plan generally must be converted to a full 401(k) with plan testing, non-discrimination rules, and higher administrative overhead — or you must terminate the solo plan and switch to a SEP or SIMPLE IRA. The SEP IRA, by contrast, scales cleanly to any number of employees.
The mega backdoor Roth involves making after-tax contributions to a solo 401(k) beyond the Roth employee deferral limit — up to the $72,000 combined limit — and then doing an in-service Roth conversion or distribution. Not all custodians support this; it requires a plan document that explicitly allows after-tax contributions and in-service distributions. When it works, it can put an additional $30,000–$40,000+ per year into Roth after already maxing the $24,500 employee deferral. The SEP IRA has no equivalent mechanism.
Yes — the solo 401(k) is a qualified plan for a business entity and requires an Employer Identification Number (EIN). You cannot use your Social Security Number. Most self-employed individuals can get an EIN in minutes at IRS.gov. This is a minor administrative step, but it's one more thing the SEP IRA doesn't require — you can open a SEP IRA using your SSN if you don't already have an EIN.
Deep dive on solo 401(k) rules — who qualifies, the mega backdoor Roth, Form 5500-EZ, and the December 31 setup deadline.
How the SEP and SIMPLE compare when you have employees — including the SIMPLE's strict 2-year rollover restriction.
All IRA, 401(k), SEP, and SIMPLE limits for 2026 in one quick-reference table.
SECURE 2.0 raised solo 401(k) catch-up limits, changed long-term part-time employee rules, and introduced new startup tax credits. The Rundown covers updates in plain English as they happen.
This guide is for general education and information only. It does not provide individualized investment, tax, or legal advice, and does not establish a client relationship. Always consult your own tax professional, financial advisor, or legal counsel before making decisions about your accounts or retirement strategy.