SEP IRA vs Solo 401(k): Which Is Best for the Self-Employed?
SEP IRA vs Solo 401(k) Comparison
| Factor | SEP IRA | Solo 401(k) |
|---|---|---|
| Eligibility | Self-employed or small business owners (with or without employees) | Self-employed with no employees (except spouse) |
| 2025 Contribution Limit | 25% of net self-employment income, up to $70,000 | $23,500 employee + 25% employer, up to $70,000 total |
| Catch-Up (age 50+) | None | $7,500 additional ($77,500 total) |
| Roth Option | No | Yes — Roth Solo 401(k) available |
| Loan Provision | No | Yes — up to 50% of balance or $50K |
| Contribution Type | Employer-only (profit-sharing) | Employee (salary deferral) + Employer (profit-sharing) |
| Setup Complexity | Very simple — one-page form | Moderate — plan document + annual filing if >$250K |
| Backdoor Roth Impact | Yes — triggers pro-rata rule | No — doesn’t affect backdoor Roth |
| Deadline to Establish | Tax filing deadline (incl. extensions) | December 31 of the tax year |
When the Solo 401(k) Wins
The Solo 401(k) is superior for most solo freelancers and consultants. The dual contribution structure (employee + employer) lets you contribute more at lower income levels. For example, if you earn $60,000 net self-employment income, a Solo 401(k) lets you defer $23,500 as the employee plus $15,000 (25% of net) as the employer — totaling $38,500. A SEP IRA would only allow $15,000 (25% of net).
The Roth option is a major advantage — you can make employee contributions as Roth (after-tax) for tax-free growth. The loan provision provides emergency liquidity. And critically, a Solo 401(k) doesn’t interfere with the backdoor Roth IRA strategy because 401(k) balances don’t trigger the pro-rata rule.
When the SEP IRA Wins
The SEP IRA’s advantage is simplicity. It’s a one-page form, no annual filings (even with large balances), and can be established as late as your tax filing deadline (including extensions). If you have employees, the SEP can cover them too (though you must contribute the same percentage for all eligible employees).
For high earners ($280K+ net self-employment income), the maximum contribution is the same for both plans ($70,000 in 2025), so the SEP’s simplicity becomes more attractive since the Solo 401(k)’s lower-income advantage disappears at that point.
Key Takeaways
- The Solo 401(k) allows higher contributions at lower income levels thanks to the dual (employee + employer) structure.
- The SEP IRA is simpler to set up and administer, with no annual filing requirements.
- Solo 401(k) offers a Roth option and loan provisions — the SEP IRA has neither.
- The SEP IRA triggers the pro-rata rule for backdoor Roth conversions; the Solo 401(k) does not.
- At very high income ($280K+), maximum contributions are identical — the SEP’s simplicity becomes more appealing.
Frequently Asked Questions
Can I have both a SEP IRA and Solo 401(k)?
Technically yes, but it rarely makes sense. Aggregate contribution limits apply across both plans, so having two doesn’t increase your total limit. Most people choose one or the other.
What is the pro-rata rule and why does it matter?
The pro-rata rule applies to Roth conversions when you have pre-tax IRA balances (including SEP IRAs). It forces you to convert proportionally from pre-tax and after-tax funds, creating an unexpected tax bill. Solo 401(k) balances are excluded from this calculation.
Can my spouse participate in my Solo 401(k)?
Yes, if your spouse earns income from the same business. A spousal Solo 401(k) effectively doubles the household contribution limit — up to $140,000 combined ($154,000 if both are 50+).
When should I set up each plan?
The Solo 401(k) must be established by December 31 of the tax year. Contributions can be made until the tax filing deadline. The SEP IRA can be established and funded anytime before the filing deadline, including extensions — giving you more time.
Do I need to file any special forms?
SEP IRA: no annual filings. Solo 401(k): you must file Form 5500-EZ annually once plan assets exceed $250,000. This is a simple one-page form but an additional administrative step.