If you're self-employed or own a small business with no full-time employees (other than a spouse), you've likely heard of both the Solo 401(k) and the SEP IRA. Both let you shelter significant income from taxes — up to $69,000 in 2025 and $70,000 in 2026. But the similarities end there. The right choice depends on your income level, whether you want Roth access, and how much complexity you're willing to manage.
Here's the complete head-to-head comparison.
Solo 401(k) vs. SEP IRA: Feature Comparison
| Feature | Solo 401(k) | SEP IRA |
|---|---|---|
| 2026 contribution limit | Up to $70,000 ($77,500 if 50+) | Up to $70,000 (25% of comp) |
| Employee deferral | $23,500 ($31,000 if 50+) | Not available |
| Employer contribution | Up to 25% of compensation | Up to 25% of compensation |
| Roth option | Yes — Roth employee deferrals | No (Roth SEP IRA available starting 2023, but few custodians offer it) |
| Loan provision | Yes — borrow up to $50K or 50% of balance | No |
| Eligibility | Self-employed with no full-time W-2 employees (spouse OK) | Any business, including those with employees |
| Employee coverage requirement | N/A (no employees allowed) | Must contribute same % for all eligible employees |
| Setup deadline | December 31 of the tax year | Tax filing deadline (incl. extensions) |
| Contribution deadline | Tax filing deadline (incl. extensions) | Tax filing deadline (incl. extensions) |
| Annual filing | Form 5500-EZ when balance exceeds $250K | None |
| Administrative complexity | Moderate | Low |
Why the Solo 401(k) Usually Wins
For most self-employed individuals and single-owner businesses, the Solo 401(k) is the better plan. Here's why:
Higher Contributions at Lower Income Levels
This is the biggest advantage. With a SEP IRA, your contribution is capped at 25% of net self-employment income. That means you need to earn $280,000 in net self-employment income to hit the $70,000 max contribution.
With a Solo 401(k), you can contribute an employee deferral of $23,500 (2026) regardless of income, plus up to 25% of compensation as the employer portion. At $100,000 in net income, the math looks like this:
That's more than double the tax-deferred savings at the same income level. For business owners earning between $50K and $250K, this gap is significant.
Roth Contributions
The Solo 401(k) lets you make employee deferrals as Roth contributions — after-tax money that grows and is withdrawn tax-free in retirement. A SEP IRA is entirely pre-tax (while SECURE 2.0 technically enabled Roth SEPs, custodian availability remains extremely limited).
If you expect your tax rate to be higher in retirement — or you simply want tax diversification — the Roth option alone may justify choosing the Solo 401(k).
Loan Provision
Need short-term access to cash? A Solo 401(k) lets you borrow up to $50,000 or 50% of your vested balance, whichever is less, and pay yourself back with interest. A SEP IRA has no loan provision — the only way to access funds is a distribution, which triggers taxes and potential penalties.
Pro tip: If you're self-employed with no employees and earning under $250K, the Solo 401(k) almost always lets you shelter more income than a SEP IRA. The employee deferral is the key advantage — it's a flat amount that doesn't depend on your income level.
When the SEP IRA Makes More Sense
The SEP IRA isn't obsolete. It has legitimate advantages in specific situations:
You have employees. If your business has W-2 employees beyond a spouse, a Solo 401(k) isn't available to you. A SEP IRA works for businesses of any size — but be aware that you must contribute the same percentage for all eligible employees. If you contribute 25% for yourself, you contribute 25% for every qualifying employee. This can get expensive quickly.
You need simplicity. A SEP IRA has virtually no administrative overhead. No annual filings, no plan documents to maintain, and setup takes minutes. A Solo 401(k) requires a written plan document and, once the account balance exceeds $250K, annual Form 5500-EZ filing.
You missed the December 31 deadline. A SEP IRA can be established and funded up to your tax filing deadline, including extensions. A Solo 401(k) must be established by December 31 of the tax year (though contributions can be made until the filing deadline). If it's February and you haven't set up a plan, the SEP is your only option for the prior year.
Your income is very high. At incomes above $280K, both plans hit the same $70,000 cap. The SEP's simplicity becomes more attractive when the contribution limits converge.
Can You Have Both?
Yes — but it rarely makes sense. If you contribute to a SEP IRA, the employer contributions reduce your available employer contribution to the Solo 401(k). The combined contribution limits don't stack; they share the same ceiling. In most cases, pick one and maximize it.
The exception: if you have a Solo 401(k) for your self-employment income and also receive a W-2 from a separate employer with its own retirement plan, those are separate limits.
Not sure which plan fits your situation? We'll model both options with your actual income numbers and show you the exact tax savings. Takes 15 minutes.
Book a Free Review →What About a Defined Benefit Plan?
If you're a high-income self-employed professional — earning $300K+ — and you want to shelter more than $70,000 per year, consider stacking a Solo 401(k) with a defined benefit plan. A DB plan can allow contributions of $200,000–$350,000+ per year depending on your age, with all contributions tax-deductible. Combined with a Solo 401(k), some business owners shelter $250K–$400K annually.
How to Set Up a Solo 401(k)
Setting up a Solo 401(k) is straightforward, but timing matters:
1. Choose a custodian. Fidelity, Schwab, and Vanguard all offer free Solo 401(k) plans. If you want Roth contributions or checkbook control (for real estate investing inside the plan), you may need a third-party administrator.
2. Establish the plan by December 31. The plan must be opened before year-end for that tax year's contributions. Don't wait until tax season.
3. Fund by your tax filing deadline. You have until April 15 (or October 15 with an extension) to make contributions for the prior year.
4. File Form 5500-EZ once the plan balance exceeds $250,000. It's a simple one-page filing due by July 31 each year.
The Bottom Line
For self-employed business owners with no employees, the Solo 401(k) beats the SEP IRA in almost every scenario that matters: higher contributions at lower income levels, Roth access, and a loan provision. The SEP's only real advantages are setup simplicity and a later establishment deadline.
If you're earning $50K–$250K in self-employment income and not maximizing a Solo 401(k), you're likely paying more in taxes than you need to. The plan is free to open at most custodians. The only cost is the 30 minutes it takes to set it up.