For self-employed business owners, consultants, freelancers, and entrepreneurs, the Solo 401(k) is one of the most powerful retirement savings tools available.
Also known as a Self-Employed 401(k) or One-Participant 401(k), this plan allows business owners with no full-time employees (other than a spouse) to make retirement contributions both as the employee and the employer, dramatically increasing the amount they can save each year.
In this guide, we explain:
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The Solo 401(k) contribution limits for 2025 and 2026
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How you can contribute to both a workplace 401(k) and a Solo 401(k)
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Contribution rules based on business entity type
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How spouses can double household contributions
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How the Mega Backdoor Roth Solo 401(k) can supercharge tax-free savings
Solo 401(k) Eligibility Requirements
Before opening a Solo 401(k), you must meet two basic requirements:
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You must have self-employment income.
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Your business cannot employ full-time non-owner employees who work more than 1,000 hours per year.
Your business may be structured as:
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Sole proprietorship
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LLC
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S-Corporation
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C-Corporation
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Partnership
If both spouses work in the same business, they can participate in the same Solo 401(k) plan, significantly increasing household retirement savings potential.
Solo 401(k) Contribution Limits (2025 and 2026)
The IRS sets two primary limits:
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Employee elective deferral
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Total contribution limit (employee + employer)
2025 Solo 401(k) Limits
| Contribution Type | Limit |
|---|---|
| Employee Deferral | $23,500 |
| Catch-Up (Age 50+) | $7,500 |
| Total Contribution Limit | $70,000 |
2026 Solo 401(k) Limits
| Contribution Type | Limit |
|---|---|
| Employee Deferral | $24,500 |
| Catch-Up (Age 50+) | $8,000 |
| Total Contribution Limit | $72,000 |
SECURE 2.0 Super Catch-Up
Individuals age 60–63 may qualify for a Super Catch-Up Contribution of $11,250.
This allows even greater retirement savings during the final years before retirement.
How Solo 401(k) Contributions Work
Because the business owner acts as both employee and employer, contributions can be made in two ways:
1. Employee Contributions
You may contribute:
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Up to 100% of compensation
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Up to the annual employee deferral limit
2. Employer Profit-Sharing Contributions
Employers may contribute:
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25% of W-2 wages (corporations)
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About 20% of net self-employment income (sole proprietors or partnerships)
This dual contribution structure allows significantly higher retirement contributions compared to many other retirement plans.
Can You Contribute to a Work 401(k) and a Solo 401(k)?
Yes.
If you have:
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A full-time job with a 401(k)
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A side business generating self-employment income
You may contribute to both plans in the same year.
However, employee salary deferrals are aggregated across all 401(k) plans.
For example:
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2026 employee deferral limit: $24,500 total
If you contribute $20,000 to your employer 401(k), you may only contribute $4,500 more as an employee contribution to your Solo 401(k).
But importantly:
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Employer contributions are NOT aggregated
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After-tax Mega Backdoor Roth contributions are NOT aggregated
This creates powerful tax planning opportunities.
Mega Backdoor Roth Solo 401(k)
One of the most powerful features of a Solo 401(k) is the Mega Backdoor Roth strategy.
This involves:
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Making voluntary after-tax contributions
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Converting those funds to the Roth Solo 401(k)
For 2026, the total contribution limit is $72,000, meaning you could potentially convert up to $72,000 per year into Roth funds using this strategy.
This allows business owners to rapidly grow tax-free retirement savings.
Contribution Rules by Business Entity
How contributions are calculated depends on your business structure.
Sole Proprietor
Contributions are based on:
Schedule C Line 31 (Net Profit)
The typical formula:
Employer Contribution ≈ 20% of Adjusted Income
Employee contributions are made up to the annual deferral limit.
S-Corporation
Contributions are based on:
W-2 Box 1 wages paid to the owner
Example:
If your S-Corp pays you:
$100,000 W-2 wages
You may contribute:
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Employee contribution up to $24,500
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Employer contribution up to 25% of wages ($25,000)
Partnership
Partners determine their contribution base using:
Schedule K-1 Line 14 Code A
Similar to sole proprietors, contributions are calculated after adjusting for half of self-employment tax.
Can Both Spouses Participate in the Same Solo 401(k)?
Yes.
If both spouses work in the same business, they may participate in the same Solo 401(k) plan.
However:
Each spouse must maintain separate accounts for each source of funds:
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Pre-tax
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Roth
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Voluntary after-tax
This means a two-participant plan typically has six sub-accounts.
Example:
| Participant | Accounts |
|---|---|
| Spouse 1 | Pre-tax, Roth, After-tax |
| Spouse 2 | Pre-tax, Roth, After-tax |
Each spouse may contribute up to the full annual contribution limit, effectively doubling household retirement savings.
For example, using 2026 limits:
$72,000 × 2 = $144,000 annual retirement contributions
Solo 401(k) Participant Loans
Another major advantage of the Solo 401(k) is the participant loan feature.
Participants may borrow:
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50% of account balance
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Up to $50,000
Example:
| Participant | Balance | Max Loan |
|---|---|---|
| Participant 1 | $80,000 | $40,000 |
| Participant 2 | $150,000 | $50,000 |
Total household borrowing capacity = $90,000.
Why the Solo 401(k) Is One of the Most Powerful Retirement Plans
For self-employed individuals, the Solo 401(k) offers:
✔ High annual contribution limits
✔ Employee + employer contributions
✔ Mega Backdoor Roth strategy
✔ Spousal participation
✔ Participant loan option
✔ Broad investment flexibility
Because of these advantages, the Solo 401(k) remains one of the most tax-efficient retirement strategies available to entrepreneurs and small business owners.
Final Thoughts
The Solo 401(k) provides an extraordinary opportunity for self-employed individuals to build substantial retirement wealth.
With contribution limits reaching:
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$70,000 in 2025
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$72,000 in 2026
—and even more when catch-up contributions and spousal participation are included—this plan can allow households to save well over $100,000 per year for retirement.
For entrepreneurs, consultants, physicians, and side-hustle earners, the Solo 401(k) is often the most powerful retirement plan available under the IRS rules.
