HOW-TO GUIDE
How to Set Up a Solo 401(k) — Self-Employed Retirement Plan Guide 2026
Step-by-step guide to establishing a Solo 401(k) — contribution limits, deadlines, Roth option, loan provisions, and Form 5500-EZ filing requirements.
Solo 401(k) Overview: Maximum Retirement Savings for the Self-Employed
A Solo 401(k) — also called an Individual 401(k) or Self-Employed 401(k) — is a retirement plan for self-employed individuals with no employees other than a spouse. It combines the features of a traditional 401(k) (employee elective deferrals) with employer profit-sharing contributions, allowing much higher contribution limits than a SEP-IRA for most self-employed individuals.
The Solo 401(k) contribution limit for 2026 is $70,000 ($77,500 if age 50+), consisting of: (1) employee elective deferrals up to $23,500 ($31,000 if age 50+); plus (2) employer profit-sharing contributions up to 25% of W-2 wages (for S-Corp owners) or approximately 20% of net SE income (for sole proprietors). The employee deferral component makes the Solo 401(k) superior to the SEP-IRA for most self-employed individuals with income under $200,000.
| Income Level | SEP-IRA Max | Solo 401(k) Max | Solo 401(k) Advantage |
|---|---|---|---|
| $50,000 net SE income | $9,293 | $23,500 + $9,293 = $32,793 | +$23,500 |
| $100,000 net SE income | $18,587 | $23,500 + $18,587 = $42,087 | +$23,500 |
| $150,000 net SE income | $27,880 | $23,500 + $27,880 = $51,380 | +$23,500 |
| $200,000 net SE income | $37,174 | $23,500 + $37,174 = $60,674 | +$23,500 |
| $280,000+ net SE income | $70,000 | $70,000 | Equal at max |
Step-by-Step Solo 401(k) Setup
Step 1 — Choose a Provider: Open a Solo 401(k) at a financial institution that offers self-employed 401(k) plans: Fidelity (no setup fee, no annual fee), Vanguard ($20/year per fund), Schwab (no setup fee, no annual fee), or a third-party administrator (for more complex plans with Roth option, loan provisions, or alternative investments). Most major brokerages offer free Solo 401(k) plans.
Step 2 — Establish the Plan by December 31: The Solo 401(k) must be established (plan document signed) by December 31 of the tax year. Unlike the SEP-IRA, you cannot set up a Solo 401(k) after year-end for the prior year. If you miss the December 31 deadline, you must use a SEP-IRA for that year.
Step 3 — Make Employee Deferrals by December 31: Employee elective deferrals must be made by December 31 of the tax year. For sole proprietors, this means you must actually transfer the money to the plan account by December 31. For S-Corp owners, the deferral is made through payroll and must be deposited within 7 business days of each payroll.
Step 4 — Make Employer Contributions by Tax Return Due Date: The employer profit-sharing contribution can be made up to the tax return due date including extensions (April 15 or October 15). This gives you flexibility to calculate the exact contribution after year-end.
Step 5 — File Form 5500-EZ When Required: When the Solo 401(k) plan balance exceeds $250,000, you must file Form 5500-EZ (Annual Return of a One-Participant Retirement Plan) by July 31 of the following year. The penalty for late filing is $250/day (up to $150,000). Set a calendar reminder for July 1 each year to check if the balance exceeds $250,000.
Roth Solo 401(k) Option
Many Solo 401(k) providers offer a Roth option, which allows you to make after-tax employee deferrals. Roth Solo 401(k) contributions are not deductible, but qualified withdrawals in retirement are tax-free. The Roth option is particularly valuable for younger self-employed individuals who expect to be in a higher tax bracket in retirement.
For 2026, the Roth Solo 401(k) deferral limit is the same as the traditional Solo 401(k) — $23,500 ($31,000 if age 50+). You can split your deferrals between traditional and Roth. The employer profit-sharing contribution must be made to the traditional (pre-tax) account — it cannot be designated as Roth.
Case Study: $46,000 Deduction Saves $17,020 in Taxes
Michael, a freelance consultant earning $150,000 of net SE income, set up a Solo 401(k) at Fidelity in November 2025. He made a $23,500 employee deferral (transferred to the plan by December 31) and a $22,500 employer profit-sharing contribution (made by October 15, 2026 with extension). Total contribution: $46,000. Tax savings: $46,000 × 37% = $17,020 in federal income tax. The Solo 401(k) setup was free at Fidelity. Compared to a SEP-IRA ($27,880 max contribution), the Solo 401(k) allowed an additional $18,120 in contributions — saving an additional $6,704 in federal taxes.
Client Conversation Script
Client: 'I have a SEP-IRA. Should I switch to a Solo 401(k)?' Practitioner: 'With your income of $120,000, the SEP-IRA allows you to contribute about $22,000. A Solo 401(k) allows you to contribute $23,500 (employee deferral) plus $22,000 (employer contribution) = $45,500 — more than double. The difference saves you about $8,700 in federal taxes. The Solo 401(k) requires a bit more setup (you need to establish the plan by December 31 and make the employee deferral by year-end), but it is free at Fidelity or Schwab. The main question: do you have any employees? If not, the Solo 401(k) is almost always better than the SEP-IRA.'
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Apply to Join the Marketplace →Frequently Asked Questions
The Solo 401(k) contribution limit for 2026 is $70,000 ($77,500 if age 50+), consisting of employee elective deferrals up to $23,500 ($31,000 if age 50+) plus employer profit-sharing contributions up to 25% of W-2 wages or approximately 20% of net SE income.
The Solo 401(k) must be established (plan document signed) by December 31 of the tax year. Unlike the SEP-IRA, you cannot set up a Solo 401(k) after year-end for the prior year. Employee deferrals must also be made by December 31.
Form 5500-EZ must be filed by July 31 of the year following the plan year when the plan balance exceeds $250,000. The penalty for late filing is $250/day (up to $150,000). File on time — the penalty is severe.
Yes — many Solo 401(k) plans allow loans up to 50% of the vested account balance or $50,000, whichever is less. The loan must be repaid within 5 years (or longer for a primary residence purchase) with interest at the prime rate + 1%. Loans from Solo 401(k)s are not taxable if repaid on time.
No — the Solo 401(k) is only available to self-employed individuals with no employees other than a spouse. If you hire employees (other than your spouse), you must convert to a regular 401(k) plan or another plan type that covers employees.
The Solo 401(k) allows higher contributions for most self-employed individuals because it includes employee elective deferrals ($23,500) in addition to employer contributions. The SEP-IRA is simpler (no December 31 deadline, no Form 5500-EZ) but has lower effective contribution limits. For self-employed individuals with income under $200,000, the Solo 401(k) almost always allows larger contributions.
No — you cannot contribute to both a Solo 401(k) and a SEP-IRA for the same business in the same year. Choose one plan. If you have multiple businesses, you may be able to have different plans for different businesses, but the combined contributions cannot exceed the annual limit.
The information on this page is intended for licensed tax professionals (CPAs, EAs, and tax attorneys) and is provided for educational and research purposes only. Tax law is complex and fact-specific — all strategies discussed are subject to limitations, phase-outs, and conditions that may not apply to every client situation. Practitioners should independently verify all information against current IRS guidance, Treasury Regulations, and applicable state law before advising clients. This content does not constitute legal or tax advice.
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