If you're self-employed — a freelancer, consultant, sole proprietor, or single-member LLC — the Solo 401(k) is likely the most powerful retirement account available to you. It allows contribution limits far exceeding most other accounts, includes Roth options, and allows participant loans. Most self-employed people either don't know it exists or assume it's complicated.
It isn't.
Disclaimer: Contribution limits and rules change annually. This article is educational. Consult a licensed tax professional or financial advisor for guidance specific to your situation.
What Is a Solo 401(k)?
Also called an Individual 401(k) or One-Participant 401(k), a Solo 401(k) is a traditional 401(k) plan for businesses with one participant — the owner, and optionally their spouse. No other employees may be covered (if you hire employees, you must move to a different plan type).
Like a traditional 401(k), the Solo 401(k) allows:
- Pre-tax contributions (reduce taxable income now, taxed on withdrawal)
- Optional Roth contributions (after-tax, tax-free growth and withdrawal)
- Tax-deferred investment growth
- A wide range of investment options depending on the custodian
Contribution Limits — Where It Gets Powerful
The Solo 401(k) has two contribution sources because the self-employed person is both employee AND employer:
Employee elective deferral: Up to $23,000 in 2024 ($30,500 if 50+). This is the same limit as an employee at a regular company.
Employer profit-sharing contribution: Up to 25% of net self-employment income (after deducting half of SE tax and the plan contribution itself). For sole proprietors, the calculation is based on net Schedule C income.
Combined maximum: $69,000 in 2024 ($76,500 if 50+), or 100% of compensation, whichever is less.
This is significantly more than a SEP-IRA for many earners at mid-range self-employment income.
Solo 401(k) vs. SEP-IRA
| Feature | Solo 401(k) | SEP-IRA | |---|---|---| | Max contribution (lower incomes) | Higher — due to employee deferral | Lower — employer-only, 25% of income | | Max contribution (high incomes) | ~$69,000 | ~$69,000 (same cap) | | Roth option | Yes | No | | Participant loans | Yes | No | | Setup complexity | Slightly more involved | Very simple | | Deadline to establish | December 31 (generally) | Tax filing deadline | | Admin requirements | Form 5500 when assets exceed $250,000 | Minimal |
Key insight: For self-employed earners with income below ~$200,000–250,000, the Solo 401(k) typically allows higher contributions because the employee deferral component isn't limited to a percentage of income.
Example: $60,000 net self-employment income
- SEP-IRA: 25% × ~$56,500 (after SE tax adjustment) ≈ $14,130 max
- Solo 401(k): $14,130 (employer) + $23,000 (employee) = $37,130 max
The Solo 401(k) enables nearly $23,000 more in retirement contributions on the same income.
The Roth Solo 401(k)
Many Solo 401(k) providers offer a Roth designation for employee contributions. Unlike a Roth IRA:
- No income limits on Roth Solo 401(k) contributions
- High earners who are phased out of Roth IRA contributions can use Roth Solo 401(k)
- Contributions are after-tax; growth and withdrawals in retirement are tax-free
A popular strategy: contribute the full $23,000 employee deferral as Roth, plus the employer profit-sharing as traditional pre-tax.
Participant Loans
Unlike IRAs or SEP-IRAs, Solo 401(k) plans may allow the participant to take a loan from the plan — up to 50% of the vested balance or $50,000, whichever is less. The loan is repaid with interest (to yourself) on a schedule.
Loans are not taxable if repaid according to terms. Default triggers taxes and penalties.
This feature provides an emergency liquidity option that IRAs don't have.
How to Set Up a Solo 401(k)
Eligibility: You must have self-employment income. The business must not have any full-time employees other than yourself (and optionally your spouse).
Choosing a custodian: Fidelity, Vanguard, Schwab, E*Trade, and TD Ameritrade all offer Solo 401(k) plans with varying investment options and features. Fidelity's Solo 401(k) is widely considered among the best — no fees, Roth option, broad investment choices.
Establish before December 31: The plan must be established by the end of the tax year you intend to make contributions for (unlike SEP-IRAs, which can be established up to your tax filing deadline).
Steps:
- Choose a custodian and complete their adoption agreement
- Apply for an EIN (Employer Identification Number) from the IRS if you don't have one
- Fund the account before your tax filing deadline (or by December 31 for the calendar year)
- Keep records of contributions by type (employee vs. employer)
Annual requirement: File IRS Form 5500 (or 5500-EZ) once the plan's assets exceed $250,000. Below that threshold, no annual filing is required.
The Spousal Addition
If your spouse earns income from the business, they can also participate in the Solo 401(k) and contribute as an employee. This doubles the contribution opportunity for families where both spouses are involved in the business.
For most self-employed individuals earning more than $30,000–40,000 in net income, the Solo 401(k) offers more tax-sheltered space than any other account available. It takes one afternoon to establish and pays dividends in tax savings for years.