1. What is a Solo 401(k)?
A Solo 401(k) is a retirement plan designed for a business owner with no employees
(other than a spouse). As a sole proprietor, you are treated as:
- Employee: You can make employee deferrals from your self‑employment income.
- Employer: Your business can make employer contributions based on net profit.
Solo 401(k) lets you shelter a large portion of your self‑employment income, even though
you do not receive a W‑2 salary from your sole proprietorship.
2. Two Types of Contributions
Employee Deferral
- Source: Your “compensation” = net earnings from self‑employment.
- Limit: Up to the annual 401(k) deferral limit (subject to your income).
- Tax effect: Reduces your personal taxable income (Form 1040).
- Important: Does not reduce Schedule C profit directly.
Employer Contribution
- Source: Your business, based on net earnings.
- Limit: Typically up to 20% of adjusted net earnings.
- Tax effect: Deducted as a business expense—reduces Schedule C profit.
- Result: Lowers both income tax and self‑employment tax.
Think of employee deferral as a personal deduction and employer contribution as a business deduction.
Together, they create powerful tax‑advantaged savings.
3. Key Requirement: Employee Deferral Cannot Create a Business Loss
For a sole proprietor, Solo 401(k) contributions are limited by your net earnings from self‑employment.
You cannot defer more than you actually earn, and your contributions must respect these boundaries:
- No negative compensation: If your net earnings are zero or negative, you cannot make employee deferrals.
- Deferral is capped: Employee deferral is limited to your net earnings (after required adjustments).
- Employer contribution: Also limited to a percentage of positive net earnings.
Example:
Net profit on Schedule C: $80,000
Adjusted net earnings (after SE tax adjustment): ≈ $73,880
Maximum employee deferral: up to the annual limit, but not more than $73,880.
Maximum employer contribution: about 20% of $73,880 ≈ $14,776.
Result: You cannot choose contributions that exceed your earnings or turn your
self‑employment income into a “negative compensation” number.
In practice, the rules themselves prevent your employee deferral from causing a “loss”—
you simply cannot contribute more than your positive net earnings.
4. Why Solo 401(k) Is So Attractive for Self‑Employed
- Higher limits than IRA: You can often contribute far more than the IRA cap.
- Flexible mix: Combine employee deferral and employer contribution to match your cash flow.
- Business + personal tax savings: Employer portion reduces Schedule C profit; employee portion reduces personal taxable income.
- Control: You decide how much to contribute each year, based on your profit.
Illustration:
Net profit: $100,000
Possible Solo 401(k) total contribution (employee + employer): tens of thousands of dollars,
all inside a tax‑advantaged account.
You keep your business profitable while shifting a large portion of income into retirement.
5. Simple Visual Summary
- Step 1: Earn profit in your sole proprietorship.
- Step 2: Use positive net earnings to fund Solo 401(k).
- Step 3: Employee deferral → personal deduction (no business loss).
- Step 4: Employer contribution → business deduction (reduces Schedule C profit).
- Step 5: Grow retirement savings in a tax‑advantaged account.
6. Solo 401(k) Providers: Vanguard vs Fidelity vs Schwab
As a self‑employed business owner, you can choose from several major financial institutions
to open a Solo 401(k). Each provider offers different levels of convenience, flexibility,
and investment options.
Fidelity Self‑Employed 401(k)
- Setup: Fully online application.
- Contributions: Employee and employer contributions can be made online.
- Roth: Roth employee deferrals supported.
- Rollovers: Accepts rollovers from old 401(k), 403(b), Solo 401(k), etc.
- Strength: Very flexible, no account fees, broad investment choices.
Schwab Individual 401(k)
- Setup: Online application available.
- Contributions: Online contribution management.
- Roth: Roth employee deferrals supported.
- Rollovers: Accepts rollovers from most qualified plans.
- Strength: Easy to use, strong ETF lineup, no account fees.
Fidelity and Schwab provide full online Solo 401(k) setup and contribution management,
making them more convenient than Vanguard which offers paper forms only for most sole proprietors.