retirement Audience: self employed 4 min read

Solo 401(k) vs. SEP IRA: Which Wins for Solopreneurs?

Self-employed? You have two main retirement options. The SEP IRA is easier, but the Solo 401(k) is usually better. Here is why.

If you are a freelancer or business owner with no employees (except a spouse), you are in a self-employed retirement sweet spot. You can choose between the SEP IRA and the Solo 401(k). Most CPAs set up SEPs because they are easy. But the Solo 401(k) is the Ferrari. For a broader look that includes SIMPLE IRAs, see our SEP IRA vs SIMPLE IRA comparison.

Key Takeaways

  • SEP IRA: Contribution limited to ~20% of net profit. Easy to set up. Triggers Pro-Rata Rule (blocks Backdoor Roth).
  • Solo 401(k): Allows $24,500 'Employee' deferral (2026) + 20% 'Employer' profit share. Higher limits at lower income.
  • Roth Option: SEP IRAs recently got specific Roth allowance, but Solo 401(k)s have done it for years.
  • Loans: You can borrow from a Solo 401(k). You cannot borrow from a SEP.

The “Low Income” Advantage

This is where the solo 401k vs sep ira comparison gets decisive. Imagine you make $50,000 profit.

  • SEP IRA: Max contribution is ~20% = $10,000.
  • Solo 401(k): You can contribute $24,500 (Employee deferral) + ~20% Employer share = ~$34,500. Winner: The Solo 401(k) lets you shelter more than triple the amount at this income level.

As income rises, the gap narrows. At roughly $130,000+ of net self-employment income, the SEP IRA’s ~20% contribution catches up to the Solo 401(k)‘s employee deferral. But even then, the Solo 401(k) wins on other features.

For a deeper look at how the Solo 401(k) strategy works in practice, see our strategy page.

The Backdoor Roth Factor

This is the killer for anyone pursuing a Backdoor Roth IRA.

  • SEP IRA: Balances count as “Traditional IRA” money. They trigger the Pro-Rata Rule, ruining your personal Backdoor Roth strategy.
  • Solo 401(k): Does NOT count for Pro-Rata. It protects your Backdoor Roth ability.

If you are a high earner who also wants to do a Backdoor Roth conversion each year, a SEP IRA can cost you thousands in unexpected taxes. The Solo 401(k) keeps the door open.

What About a Defined Benefit Plan?

If your self-employment income is consistently above $200,000 and you want to shelter even more, a defined benefit plan lets you contribute $100,000+ per year on a tax-deferred basis. These are more complex and expensive to administer, but for high-earning solopreneurs they can be layered on top of a Solo 401(k).

Self-Employed Retirement: Other Considerations

  • Deadlines: A Solo 401(k) must be established by December 31 of the tax year (add this to your year-end tax checklist). A SEP IRA can be opened and funded up to your tax filing deadline (including extensions).
  • Paperwork: A Solo 401(k) requires Form 5500-EZ once assets exceed $250,000. A SEP has no annual filing requirement.
  • Spousal contributions: If your spouse works in the business, a Solo 401(k) lets them make their own $24,500 deferral, effectively doubling the household shelter.
  • Self-employment tax: Remember that self-employment tax (15.3% for Social Security + Medicare) applies on top of income tax. Employer contributions to either plan reduce your AGI but not your SE tax base.
  • Roth 401(k): The Solo 401(k) offers a Roth option, letting you make after-tax contributions that grow tax-free. SEP IRAs do not have an established Roth option at most custodians.

Verdict: Unless you plan to hire employees soon (which kills the Solo 401k), choose the Solo 401(k).

How sharper.tax Helps

sharper.tax analyzes your uploaded return and identifies your self-employment income, existing retirement contributions, and whether a SEP IRA or Solo 401(k) would save you more. We model the contribution limits at your specific income level so you can see the difference in real dollars. Sophisticated tax planning used to require a high-end CPA --- we make it available for free.

Sources

The information above is educational and not tax advice.