Understanding Solo 401(k) Contribution Limits
A Solo 401(k), also known as an Individual 401(k), is a powerful retirement savings vehicle designed for self-employed individuals and small business owners with no employees (other than a spouse). It allows you to contribute in two capacities: as an employee and as an employer.
2025 Solo 401(k) Contribution Limits
| Contribution Type |
Under Age 50 |
Age 50+ |
| Employee Elective Deferral |
$23,500 |
$31,000 |
| Employer Profit-Sharing (max) |
Up to 25% of compensation |
Up to 25% of compensation |
| Total Contribution Limit |
$70,000 |
$77,500 |
Employee Deferral
As the employee, you can elect to defer up to $23,500 of your compensation in 2025 (or $31,000 if age 50 or older, including $7,500 catch-up). This is the same limit that applies to traditional 401(k) plans. If you also participate in another employer's 401(k) plan, the limit is shared across all plans.
Employer Profit-Sharing Contribution
As the employer, you can contribute up to 25% of your compensation as a profit-sharing contribution. For self-employed individuals, compensation is calculated as net earnings from self-employment minus half of your self-employment tax and the employee deferral. In practice, this works out to roughly 20% of your net self-employment income for the employer contribution portion.
Total Limit
The combined employee + employer contributions cannot exceed $70,000 in 2025 (or $77,500 if age 50+). Additionally, total contributions cannot exceed 100% of your compensation.
Tax Deduction
All Solo 401(k) contributions are tax-deductible (if using the traditional version), reducing your taxable income dollar-for-dollar. This makes the Solo 401(k) one of the most tax-efficient ways to save for retirement as a self-employed individual.
Eligibility Requirements
- You are self-employed (sole proprietor, independent contractor, or single-member LLC)
- You have no employees other than a spouse (if the spouse works for the business)
- You have net self-employment income (positive earnings from your business)
- A Solo 401(k) can be established by partnerships, corporations, and LLCs as long as there are no non-owner employees
Deadlines to Set Up a Solo 401(k)
A Solo 401(k) must be established by the last day of the tax year (December 31 for calendar-year taxpayers) to make employee deferrals for that year. However, employer profit-sharing contributions can be made up to the tax filing deadline (including extensions).
Frequently Asked Questions
Can I have both a Solo 401(k) and a traditional 401(k) through an employer?
Yes, but the employee deferral limit ($23,500 in 2025, or $31,000 if 50+) is shared across all 401(k) plans. If you contribute $10,000 through your day job's 401(k), you can only contribute $13,500 more through your Solo 401(k) as an employee deferral. However, the employer profit-sharing contribution to your Solo 401(k) is separate and does not count toward this limit.
Can I contribute 100% of my income to a Solo 401(k)?
No, total contributions are capped at the IRS limits. The employee deferral is limited to $23,500 (under 50) or $31,000 (50+), and total combined contributions cannot exceed $70,000 (or $77,500 if 50+) or 100% of your compensation — whichever is less. Your actual net income also determines the employer contribution, which is calculated as a percentage of your earnings.
When is the deadline to make Solo 401(k) contributions?
Employee salary deferrals must be made by the end of the tax year (December 31). Employer profit-sharing contributions can be made up to the tax filing deadline, including extensions (typically April 15 or October 15 for sole proprietors). You must formally adopt the Solo 401(k) plan by December 31 of the tax year to make employee deferrals for that year.
Is a Solo 401(k) better than a SEP IRA?
For many self-employed individuals, yes. A Solo 401(k) generally allows higher total contributions ($70,000 vs. $69,000 for SEP IRA in 2025) and offers catch-up contributions for those 50+ (SEP IRAs have no catch-up provision). Solo 401(k)s also allow Roth contributions and loan provisions. However, SEP IRAs are simpler to set up and have no filing requirements regardless of balance. The best choice depends on your specific situation.
Do I need to file Form 5500 for my Solo 401(k)?
If your Solo 401(k) assets exceed $250,000 at the end of the plan year, you must file Form 5500-EZ annually. This is an informational return — no taxes are due. Many Solo 401(k) providers help with this filing. Below $250,000 in assets, no annual filing is required, making it very low-maintenance for smaller accounts.
Can my spouse participate in my Solo 401(k)?
Yes! If your spouse works for your business, they can also participate in the Solo 401(k) plan. They can make their own employee deferrals (up to $23,500 or $31,000 if 50+) and receive employer profit-sharing contributions. This effectively doubles the tax-advantaged contribution room for a married couple running a business together.