Solo 401(k): The Best Retirement Account Most Self-Employed People Miss

If you are self-employed without full-time employees, the Solo 401(k) is almost certainly the best retirement account available to you. It allows higher contributions than a SEP IRA at most income levels, offers a Roth option, and permits loans against the balance in ways no IRA allows.

Most self-employed people have never set one up, often because it sounds complicated. It is not. It requires a one-time plan adoption document and a brokerage account, and most major brokerages handle the setup in under an hour.

What a Solo 401(k) Is

A Solo 401(k), also called an Individual 401(k) or Self-Employed 401(k), is a standard 401(k) plan for businesses with no full-time employees other than the owner and the owner's spouse. It follows the same IRS rules as an employer 401(k), including the same contribution limits.

The critical advantage over a SEP IRA or SIMPLE IRA is the two-bucket contribution structure.

2026 Contribution Limits: The Two Buckets

A Solo 401(k) allows contributions from two separate sources:

Employee elective deferrals: As the employee of your own business, you can defer up to $23,500 in 2026. Catch-up contribution rules for 2026:

• Age 50-59: additional $7,500 (total $31,000)
• Age 60-63: additional $11,250 (total $34,750) -- enhanced under SECURE 2.0
• Age 64 and older: additional $7,500 (total $31,000)

Employer profit-sharing contributions: As the employer, you can contribute up to 25% of net self-employment income (after subtracting half of self-employment tax).

Combined limit: The total from both buckets cannot exceed $70,000 in 2026 ($77,500 or more with catch-up contributions depending on age).

Why does this matter? Because the employee contribution bucket is not a percentage of income. Even at relatively low income, you can contribute the full employee deferral amount.

Solo 401(k) vs SEP IRA at Different Income Levels

This table illustrates why the Solo 401(k) usually wins at lower and moderate income levels:

At nearly every income level below the maximum contribution cap, the Solo 401(k) allows significantly higher total contributions. The gap closes and eventually disappears only at very high incomes where the 25% employer contribution alone approaches the plan maximum.

The Roth Solo 401(k) Option

One of the most significant advantages of the Solo 401(k) over the SEP IRA: the employee elective deferral can be made as Roth contributions.

A Roth Solo 401(k) uses after-tax dollars on the employee deferral portion. The money grows tax-free and is withdrawn tax-free in retirement. Unlike a Roth IRA, there are no income limits restricting who can make Roth Solo 401(k) contributions. High earners who are phased out of direct Roth IRA contributions can still make Roth contributions through the Solo 401(k) employee deferral.

Not all providers offer the Roth option on Solo 401(k)s. Fidelity and Charles Schwab both offer Roth Solo 401(k) options. Vanguard does not currently offer the Roth employee deferral.

Loan Provision

Solo 401(k)s can include a loan provision allowing you to borrow from your own account balance. The IRS allows loans up to the lesser of $50,000 or 50% of the vested account balance. Loans must be repaid within five years at a reasonable interest rate (the interest goes back to your own account).

This is not a feature available in any IRA type (traditional, Roth, or SEP). It provides a liquidity option in emergencies without triggering taxes or penalties, though using it reduces your account's growth and should be considered carefully.

Eligibility Requirements

To open and contribute to a Solo 401(k), you must:

• Have self-employment income (sole proprietor, single-member LLC, partnership, S-corp owner)
• Have no full-time W-2 employees other than yourself or your spouse

If you have a part-time employee working fewer than 1,000 hours per year (or fewer than 500 hours under newer SECURE Act rules that phase in through 2025), they may not trigger a full plan qualification requirement, but rules here are nuanced. Once you hire full-time employees, a Solo 401(k) is no longer appropriate and you would need to transition to a traditional 401(k) plan.

How to Open a Solo 401(k)

Important deadline: The Solo 401(k) plan must be established (signed plan documents) by December 31 of the tax year for which you want to contribute. You cannot establish a Solo 401(k) after year-end for the prior year, unlike a SEP IRA. Contributions, however, can be made until the tax filing deadline including extensions.

Steps:

1. Choose a provider: Fidelity, Schwab, and TD Ameritrade (now part of Schwab) offer no-fee Solo 401(k)s with good investment options. For Roth contributions specifically, Fidelity is a strong choice.
2. Complete the adoption agreement and plan document. The provider handles this.
3. Note the plan establishment date on your records.
4. Open the account and begin investing. Employee deferral contributions must be deposited within a reasonable time after the pay date (typically 7-15 business days).
5. File IRS Form 5500-EZ annually once your plan balance exceeds $250,000.

Real-World Examples

Example: Nina, 34, freelance copywriter earning $75,000 net

Situation: Nina had been using a SEP IRA and contributing approximately $18,000 per year. Her accountant explained the Solo 401(k) comparison.

What she switched to: A Solo 401(k) with the Roth employee deferral option at Fidelity. She now contributes $23,500 as Roth employee deferrals (tax-free growth forever) plus approximately $14,800 as a pre-tax employer contribution.

Result: Total 2026 contribution of $38,300, up from $18,000, and the Roth component means $23,500 grows completely tax-free. At her 22% marginal rate, the pre-tax employer contribution saves roughly $3,256 in federal taxes this year.

Example: Jerome, 52, consultant with irregular income

Situation: Jerome has a strong year ($180,000 net) followed by a moderate year ($90,000 net). He wants maximum flexibility.

What he uses: A Solo 401(k). In the strong year, he contributes $31,000 as employee deferrals (age 50 catch-up) plus $40,000 as employer (25% of net), totaling $71,000. In the moderate year, he contributes $31,000 employee plus $20,000 employer, totaling $51,000. The flexibility to scale with income is identical to a SEP IRA but with a consistently higher ceiling.

Common Mistakes

Missing the December 31 plan establishment deadline. You must open and sign plan documents by December 31 to contribute for that tax year. If you miss this, a SEP IRA (which can be opened up until tax filing) is your fallback for prior-year contributions.

Confusing the employee and employer contribution limits. The $23,500 employee limit applies per person across all employer plans. If you also have a W-2 job with a 401(k) where you contributed $10,000, you can only contribute $13,500 as the employee in your Solo 401(k) that year.

Not filing Form 5500-EZ when the balance crosses $250,000. This is an IRS requirement, not optional. Penalties for not filing are $250 per day, capped at $150,000.

For the direct comparison with the SEP IRA, see What Is a SEP IRA and Who Actually Benefits From One?. And if you are deciding between pre-tax and Roth contributions, the framework in 401(k) vs Roth IRA at 22: Which Comes First? applies equally to self-employed retirement account decisions.

This post is for informational purposes only and does not constitute financial, tax, or legal advice. Contribution limits and plan rules are subject to annual IRS adjustments. Consult a qualified tax professional for guidance specific to your situation.