Solo 401(k) vs SEP-IRA for the self-employed
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When you're self-employed, no employer is quietly funding a 401(k) for you — but you get something in return: two of the most generous retirement accounts available, the Solo 401(k) and the SEP-IRA. Both let you shelter a large chunk of income from taxes today while building a nest egg. The catch is choosing between them, because they're structured differently and suit different situations.
This guide explains how each works, how their contribution structures differ, the tax benefits, and who each one fits — in plain language, without pretending there's a single right answer. Because the exact dollar limits change every year, we'll describe the structure and repeatedly point you to verify current-year figures.
How each account is built
The SEP-IRA
A Simplified Employee Pension (SEP) IRA is exactly what its name suggests: simple. You contribute as the "employer" — a percentage of your net self-employment income, up to an annual cap. There's no separate employee contribution. Setup is fast, paperwork is minimal, and there's typically no annual government filing until the account grows quite large. The trade-off is flexibility: because it only uses the employer-style contribution, you may not be able to save as much at lower incomes as you could in a Solo 401(k).
One important rule if you have staff: a SEP-IRA can cover employees, but you must contribute the same percentage of pay for every eligible employee as you do for yourself. That's fine when it's just you — but it can get expensive if you have a team.
The Solo 401(k)
A Solo 401(k) (also called an individual or one-participant 401(k)) is designed for a business with no full-time employees besides the owner and a spouse. Its superpower is that you contribute in two capacities:
- As the employee: a salary-deferral contribution, up to an annual limit.
- As the employer: an additional profit-sharing contribution, a percentage of net self-employment income.
Because those two stack, a Solo 401(k) often lets you reach a higher total contribution than a SEP-IRA at the same income — especially at low-to-middle incomes, where the flat employee deferral does a lot of work. Many Solo 401(k) plans also offer a Roth option for the employee portion (contribute after-tax now, withdraw tax-free later), and some allow loans from the balance. The cost is a little more administration, and once assets pass a threshold you may need to file an annual information return.
Side-by-side comparison
| Feature | Solo 401(k) | SEP-IRA |
|---|---|---|
| Contribution structure | Employee deferral + employer profit-sharing (two parts stack) | Employer contribution only (one part) |
| Relative contribution room | Often higher at low-to-middle income | Can match at higher income; simpler math |
| Roth option | Frequently available for the employee portion | Generally not (traditional pre-tax) |
| Loans | Sometimes allowed by the plan | Not allowed |
| Employees | Designed for owner (and spouse) only | Can include employees — but you must fund them equally by percentage |
| Setup & admin | A bit more paperwork; possible annual filing above an asset threshold | Very simple; minimal filing |
Contribution limits, income caps, and filing thresholds change every year. Verify current-year limits with the IRS or your plan provider before contributing.
The tax benefits
Both accounts deliver the core self-employed retirement tax win: contributions to the traditional (pre-tax) version reduce your taxable income for the year, and the money grows tax-deferred until you withdraw it in retirement. For a self-employed person in a meaningful tax bracket, that deduction can be substantial — it's one of the few large, legitimate levers left after your business deductions.
The Solo 401(k) adds a wrinkle worth understanding: its Roth option lets you skip the deduction now in exchange for tax-free withdrawals later. That can be the better deal if you expect higher tax rates in the future or simply want tax-free income in retirement. A SEP-IRA is traditionally pre-tax only, so it's a pure "deduct now" play.
Whichever you choose, coordinate it with the rest of your tax picture. Knowing your net income drives how much you can contribute — our self-employed tax calculator helps you estimate that, and our deductions guide covers the write-offs that come first.
Who each one suits
Lean toward a Solo 401(k) if…
- You have no full-time employees (just you, or you and a spouse).
- You want to contribute as much as possible, especially at low-to-middle income.
- You'd value a Roth option or the ability to borrow from the plan.
- You're comfortable with slightly more setup and paperwork.
Lean toward a SEP-IRA if…
- You prize simplicity and want to open and fund it fast.
- You have (or plan to add) employees and want a straightforward plan — accepting that you'll fund them at the same percentage.
- Your income is high enough that the two plans' contribution room converges anyway.
- You want minimal ongoing administration.
Where to open one
Both account types are widely available. The right provider depends on which account you choose and how hands-on you want to be. Check current fees, investment options, and whether Roth and loan features are supported before opening.
[Affiliate: Solo 401(k) Provider]
A specialist Solo 401(k) provider that supports the features that make these plans attractive — employee and employer contributions, and often Roth and loan options. Best if you've decided a Solo 401(k) fits and want a plan built specifically for it. Downside: specialist plans can carry setup or annual fees that a plain IRA wouldn't, so weigh the cost against the extra flexibility. Verify current fees and features.
[Affiliate: Robo / IRA Provider]
A low-cost brokerage or robo-advisor that offers SEP-IRAs (and often Solo 401(k)s) with simple, automated investing. Best if you want a hands-off, low-fee home for retirement money without managing individual investments. Downside: automated platforms offer less customization, and not every one supports the full range of Solo 401(k) features — confirm what's available and check current pricing.
A calm way to decide
- Do you have full-time employees? If yes, a Solo 401(k) is off the table — compare a SEP-IRA against other small-business plans.
- Just you (and maybe a spouse)? Estimate contributions both ways at your income using current-year limits.
- Want Roth or a loan feature? That points to a Solo 401(k).
- Want maximum simplicity? That points to a SEP-IRA.
- Still unsure? A SEP-IRA is easy to start now and you can move to a Solo 401(k) later as your income and needs grow.
The most important decision isn't which of these two you pick — it's that you pick one and start. Both turn irregular self-employed income into long-term security and a real tax break today. Choose the one you'll actually maintain, verify this year's limits, and fund it consistently.
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Frequently asked questions
Which lets me contribute more, a Solo 401(k) or a SEP-IRA?
At lower and middle income levels, a Solo 401(k) usually allows a larger contribution because it combines an employee salary deferral with an employer profit-sharing contribution, while a SEP-IRA uses only the employer-style contribution. At higher income the two can converge. Verify current-year limits before deciding, since they change annually.
Can I have employees with a Solo 401(k)?
A Solo 401(k) is designed for a business with no full-time employees other than the owner and a spouse. If you hire full-time W-2 employees, you generally can't keep using it and would need a different plan. A SEP-IRA can include employees, but you must contribute the same percentage for eligible employees as for yourself.
Is a Solo 401(k) or SEP-IRA harder to set up?
A SEP-IRA is simpler — quick to open, minimal paperwork, and no annual filing until it grows large. A Solo 401(k) has slightly more setup and may require an annual information return once assets exceed a threshold, but it offers features like salary deferral, potential Roth options, and sometimes loans.
Can I switch from a SEP-IRA to a Solo 401(k) later?
Often yes. Many self-employed people start with a SEP-IRA for simplicity and move to a Solo 401(k) as income grows or they want higher contributions or Roth options. The mechanics of rolling over or coordinating plans can be nuanced, so confirm the steps with the provider or a tax professional.
Educational information only — not tax, legal, or investment advice. Contribution limits, income caps, deadlines, and filing thresholds change every year and depend on your specific situation. Verify current-year limits with the IRS and confirm details with your plan provider or a tax professional before contributing. Keldwell may earn affiliate commissions from some links on this page.