The Solo 401(k) offers one of the highest contribution ceilings available to self-employed individuals. In 2026, a qualifying participant can contribute up to $72,000 to the plan, or $83,250 with the catch-up available to ages 60 through 63. What makes that possible is a dual-contribution structure found in no other self-directed plan type: you contribute once as the employee of your business, and again as the employer.
This page explains how each contribution type works, how the limits are calculated based on business structure, age-based catch-up provisions, and contribution deadlines. Because your specific allowable amount depends on net business income, business entity type, and other retirement plan participation, we encourage you to work with a qualified tax advisor on contribution strategy. The limits below define the ceiling; your advisor helps you determine the optimal amount for your situation.
2026 Solo 401(k) contribution limits
Source: IRS Notice 2025-67 | Effective for the 2026 tax year
| Contribution Type | 2026 Limit |
|---|---|
| Employee Salary Deferral | $24,500 |
| Employer Profit-Sharing (W-2 wages) | Up to 25% of W-2 wages |
| Employer Profit-Sharing (Self-employed) | Up to 20% of net self-employment income |
| Catch-Up (Age 50-59 or Age 64+) | $8,000 |
| Super Catch-Up (Age 60-63) | $11,250 |
| Plan Maximum (Under age 50) | $72,000 |
| Plan Maximum (Age 50-59 or Age 64+) | $80,000 |
| Plan Maximum (Age 60-63) | $83,250 |
Maximum compensation considered for calculations: $360,000 (IRC §401(a)(17))
How the two contribution types work together
The Solo 401(k)'s contribution power comes from stacking two legally distinct contribution sources.
Employee salary deferrals operate exactly like a traditional 401(k) at any employer. You defer a portion of your compensation into the plan, pre-tax or Roth, up to the annual employee limit. This amount is shared across all 401(k)-type plans you participate in during the year; it is not per-plan.
Employer profit-sharing contributions are made by the business itself. They may be designated as Traditional (pre-tax) or Roth, calculated as a percentage of qualifying compensation, and carry their own limit separate from employee deferrals. They do not reduce your employee deferral capacity, and your employee deferral does not reduce what the business can contribute; the two work in parallel.
Combining these sources is how eligible participants reach the plan maximum. A self-employed consultant earning $200,000 in net business income, for example, could contribute $24,500 as the employee and add an employer contribution up to 20% of net self-employment income, working toward the $72,000 plan ceiling.
Employer profit-sharing: the calculation differs by business structure
How you pay yourself determines how the employer contribution is calculated.
S-corporation or C-corporation (W-2 wages): The employer contribution can be up to 25% of your W-2 wages. Shareholder distributions do not count for this purpose; only W-2 compensation is included in the base.
Sole proprietorship or single-member LLC (pass-through / self-employed): The calculation uses net self-employment income after deducting half of self-employment taxes. Because the employer contribution itself reduces the base before the percentage is applied, the effective contribution rate works out to approximately 20% of net profit after the SE tax deduction. IRS Publication 560 contains the specific worksheet for this calculation.
In either structure, the employer contribution is capped at the lesser of the applicable percentage or the plan maximum remaining after any employee deferrals.
Catch-up contributions: age 50 and beyond
Participants who turn 50 or older during the calendar year can make additional employee deferrals beyond the standard limit.
In 2026, the standard catch-up is $8,000, raising total employee deferral capacity to $32,500 and the plan maximum to $80,000 for participants ages 50 through 59 and 64 and older.
SECURE 2.0 Act created an enhanced "super catch-up" for participants who turn 60, 61, 62, or 63 during the tax year. These participants contribute $11,250 as their catch-up rather than $8,000, raising total employee deferral capacity to $35,750 and the plan maximum to $83,250. At age 64, participants return to the standard $8,000 catch-up.
Important: Participants with prior-year FICA wages exceeding $150,000 are required under IRC §414(v)(7)(A) to designate all catch-up contributions as Roth contributions in 2026. Pre-tax catch-up contributions are not available to participants above this wage threshold. Regular salary deferrals remain your choice of Traditional or Roth regardless of income.
A fourth contribution type: nondeductible
The Solo 401(k) supports a fourth contribution type: nondeductible (after-tax) employee contributions. These are not subject to the standard deferral limit and can be used to fill the gap between your compensation-based allowable contributions and the plan maximum.
Nondeductible contributions are not tax-deductible, but earnings grow tax-deferred. Their real value lies in the Mega Backdoor Roth strategy, where after-tax contributions are converted to Roth inside the plan, allowing for tax-free growth.
Not all Solo 401(k) plan documents support this feature. Self-Directed Plans Solo 401(k)s do.
Contribution deadlines
Deadlines depend on three things: the contribution type, how the business pays you, and whether the plan was already in place during the tax year. SECURE 2.0 expanded what a self-employed filer can do after December 31, but the expansion is narrower than it is often described.
| Contribution Type | Plan Must Be Established By | Contribution Must Be Funded By |
|---|---|---|
| Employee deferral, sole proprietor or pass-through, plan in place during the tax year | December 31 of the plan year | Tax filing deadline, including extensions |
| Employee deferral, sole proprietor or pass-through, first plan year, plan adopted after year end | Tax filing deadline, without extensions | Tax filing deadline, without extensions |
| Employee deferral, W-2 or corporate environment | December 31 of the plan year | December 31 of the plan year |
| Employer profit-sharing | Tax filing deadline, including extensions | Tax filing deadline, including extensions |
For a sole proprietor or single-member LLC with a plan already established during the tax year, the extended deadline generally runs through October 15 of the following calendar year. There is no payroll event in a pass-through structure, so employee deferrals are funded against income determined at filing rather than withheld during the year.
A plan adopted after the tax year has ended is a different case. Under Section 317 of the SECURE 2.0 Act, a sole proprietor with no employees may adopt a Solo 401(k) after December 31 and still make employee deferrals for the prior year, but that window closes on the tax filing deadline without regard to extensions, generally April 15. Filing an extension does not move it. Employer profit-sharing contributions to the same plan remain available through the extended deadline.
The W-2 exception runs the other way. If your business pays you through payroll, employee deferrals are withheld from wages, and wages cannot be reduced retroactively. The final payroll of the year is the last opportunity to make an employee deferral for that tax year. Funds from that final payroll are customarily deposited in the days that follow, consistent with ordinary payroll processing, but the opportunity itself closes with the calendar year and no later adoption or extension reopens it.
Employer profit-sharing contributions follow the business tax filing deadline including extensions in either structure. IRS Publication 560 is the governing reference for all of the above, and your CPA can confirm which filing deadline applies to your return.
Contribution limits vs. contribution strategy
The limits on this page define what the IRS permits. They do not define what is right for your situation.
Contribution strategy, how much to contribute, whether to elect Traditional or Roth treatment, and how to sequence contributions across a year of variable income, depends on your tax position, income projections, and broader financial picture. For guidance on optimizing contributions for your specific circumstances, consult a CPA or tax professional with experience in self-employment retirement planning.
IRS Publication 560 (Retirement Plans for Small Business) is the primary reference for contribution calculations and is updated annually.
Disclosure
This information is provided for educational purposes only and should not be interpreted as tax, legal, or investment advice. Readers are encouraged to consult a qualified professional who can offer guidance based on their personal situation.