What is a Solo 401(k)?
A Solo 401(k) — also called an individual 401(k) or self-employed 401(k) — is a tax-advantaged retirement plan designed for self-employed individuals and small business owners with no employees other than themselves (and a spouse). It combines the benefits of a traditional 401(k) with higher contribution limits that are only available when you work for yourself.
Unlike a SEP-IRA, a Solo 401(k) allows you to contribute as both an employee and an employer. This dual contribution structure lets self-employed individuals shelter significantly more income from taxes each year. The plan is available to sole proprietors, single-member LLC owners, S-corporation owners, partnerships, and other self-employed structures.
Who Qualifies for a Solo 401(k)?
To open and contribute to a Solo 401(k), you must meet two criteria:
- **Self-employment income**: You must have net self-employment income from a business, freelance work, consulting, or other self-employed activity. - **No full-time employees**: You cannot have any employees other than yourself and your spouse. If you hire even one part-time employee who meets IRS eligibility rules, you may no longer qualify for a Solo 401(k) and may need to convert to a different plan type.
Common qualifying situations include sole proprietors filing Schedule C, single-member LLC owners, S-corporation shareholders who pay themselves a W-2 salary, and independent contractors. Spouses who are employed by the business may also participate.
Employee vs. Employer Contributions Explained
A Solo 401(k) has two separate contribution buckets, each with its own rules:
**Employee Elective Deferral** As the employee of your own business, you can contribute up to 100% of your compensation, subject to the IRS annual deferral limit. This limit is the same ceiling that applies to W-2 employees at large corporations. You can contribute pre-tax (traditional) or after-tax (Roth, if your plan allows), or a combination of both.
**Employer Profit-Sharing Contribution** As the employer, you can make an additional profit-sharing contribution on top of your employee deferral. For S-corporations, this is up to 25% of your W-2 wages from the S-corp. For sole proprietors, the IRS formula works out to approximately 20% of your net self-employment income (after subtracting the deductible half of self-employment tax).
**Combined Annual Limit** The total of both contributions — employee deferral plus employer profit sharing — cannot exceed the IRS combined annual additions limit (the Section 415 limit). This combined cap is substantially higher than what any individual can contribute to a traditional employer 401(k) alone, making the Solo 401(k) one of the most powerful retirement savings vehicles available.
Catch-Up Contributions and SECURE 2.0
If you are age 50 or older, you can make additional catch-up contributions above the standard employee deferral limit.
**Standard Catch-Up (Ages 50-59 and 64+)** Participants age 50 or older can contribute an extra catch-up amount on top of the base employee deferral limit each year.
**Enhanced Catch-Up for Ages 60-63 (SECURE 2.0 Act)** Starting in 2025, the SECURE 2.0 Act introduced a special enhanced catch-up for participants aged 60 through 63. This enhanced amount is higher than the standard 50+ catch-up and is one of the most significant retirement savings improvements enacted in recent years. Once you turn 64, the catch-up reverts to the standard 50+ amount.
Catch-up contributions apply only to the employee deferral portion — not to the employer profit-sharing contribution — but they do count toward the combined annual limit calculation.
S-Corp vs. Sole Proprietor Differences
The calculation method differs depending on your business structure:
**Sole Proprietor / Single-Member LLC** Your compensation base is your net self-employment income minus the deductible portion of self-employment (SE) tax. Because the IRS lets you deduct half of your SE tax before calculating contributions, the effective profit-sharing rate works out to roughly 20% of your gross net self-employment income (as opposed to the stated 25% rate applied after the deduction).
**S-Corporation** Your compensation base for Solo 401(k) purposes is your W-2 salary from the S-corp — not the total distributions you take. The employer profit-sharing contribution is 25% of that W-2 salary. This is one reason why the W-2 salary you set for yourself in an S-corp has significant retirement planning implications. A salary that is too low reduces your allowable profit-sharing contribution.
How to Use This Calculator
1. Select your business type: Sole Proprietor or S-Corporation. 2. Enter your net self-employment income (sole proprietors) or your W-2 salary from the S-corp (S-corp owners). 3. Enter your age. This determines whether catch-up contributions apply and which catch-up amount to use. 4. Optionally enter a desired employee contribution amount. Leave it at 0 to have the calculator show the maximum possible employee deferral. 5. Click Calculate Maximum Contributions. The calculator fetches current IRS limits from our AI service and then computes your employee deferral, employer profit sharing, and total maximum contribution. 6. Review your results, including the contribution breakdown chart and the percentage of the combined annual limit you would use.
FAQs
**Q: Can I contribute to both a Solo 401(k) and a SEP-IRA in the same year?** A: Generally no — you cannot contribute to both a Solo 401(k) and a SEP-IRA for the same business in the same year. If you have multiple businesses, different rules may apply. Consult a tax professional for multi-business situations.
**Q: What is the deadline to open a Solo 401(k)?** A: You must establish the plan by December 31 of the tax year you want to contribute for. The deadline to make contributions is your tax filing deadline (including extensions), which can extend into the following year.
**Q: Can my spouse contribute to a Solo 401(k)?** A: Yes, if your spouse earns compensation from your business, they can participate in the same Solo 401(k) plan and contribute their own employee deferral and profit-sharing amounts.
**Q: What happens if I exceed the contribution limits?** A: Excess contributions must be withdrawn (with earnings) by the tax filing deadline or you will face excise taxes. This is why accurate calculation before contributing is important.
**Q: Does the calculator account for Roth Solo 401(k) contributions?** A: The contribution limits are the same whether you contribute pre-tax (traditional) or after-tax (Roth). This calculator shows the maximum total contributions regardless of which type you choose.
**Q: Are Solo 401(k) contributions tax-deductible?** A: Traditional (pre-tax) contributions reduce your taxable income in the year you make them. Roth contributions are made with after-tax dollars but grow tax-free. The employer profit-sharing portion is always deductible as a business expense.
**Q: What is the Section 415 combined limit?** A: Section 415 of the IRS code sets the maximum total amount that can be added to a defined contribution plan in a year. For Solo 401(k)s, the combined limit is the ceiling on all contributions (employee + employer) from all sources.
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