Solo 401(k) Contribution Limits by Entity Type: LLC vs S Corp vs C Corp (2026)
Quick Answer
In 2026, the Solo 401(k) total contribution limit is $70,000 ($77,500 if you’re 50 or older). Your entity type dramatically affects how you get there: LLC owners contribute based on net business income, S Corp owners split contributions between W-2 salary and corporate profit-sharing, and C Corp owners can leverage after-tax contributions for Mega Backdoor Roth conversions. For most business owners earning $100,000–$300,000, an S Corp structure maximizes retirement contributions while minimizing overall taxes, but LLCs win at lower income levels due to simpler contribution calculations.
Key Takeaways
- 2026 Solo 401(k) limit: $70,000 total ($23,500 employee deferral + $46,500 employer contribution), with a $7,500 catch-up for owners aged 50+
- LLC (sole prop): Employer contribution = 25% of adjusted net profit (after deducting self-employment tax and contribution itself)
- S Corp: Employer contribution = 25% of W-2 wages, meaning your salary directly controls your maximum contribution
- C Corp: Can enable Mega Backdoor Roth contributions up to $46,500 in after-tax dollars on top of pre-tax limits
- Best entity for Solo 401(k): S Corps for $100K–$300K income range; LLCs for simplicity at lower incomes; C Corps for Roth conversion strategies
- SECURE 2.0 enhancements: Roth catch-up contributions are now mandatory for high earners (>$145,000), and Starter 401(k) plans offer streamlined setup
Why Entity Choice Matters for Solo 401(k) Contributions
Your business entity determines two critical factors for retirement planning:
- How contributions are calculated — based on net business income (LLC) vs. W-2 wages (S Corp) vs. corporate compensation (C Corp)
- Which tax benefits you receive — deductions at the personal level, corporate level, or both
The same $70,000 contribution limit applies regardless of entity, but the path to reaching that limit — and the tax efficiency of each dollar along the way — varies significantly.
The Three Contribution Buckets
Every Solo 401(k) has up to three contribution channels:
| Contribution Type | 2026 Limit | Who Makes It |
|---|---|---|
| Employee Deferral (pre-tax or Roth) | $23,500 ($31,000 if 50+) | You, from personal compensation |
| Employer Profit-Sharing | Up to 25% of compensation | The business entity |
| After-Tax (Mega Backdoor Roth) | Up to $46,500 additional | You, if plan permits |
The combined total across all three cannot exceed $70,000 ($77,500 with catch-up) in 2026.
Solo 401(k) for LLC Owners (Sole Proprietorship Taxation)
How It Works
When your LLC is taxed as a sole proprietorship (the default for single-member LLCs), your Solo 401(k) contributions are based on your net self-employment income — not a W-2 salary.
Contribution Calculation
- Employee Deferral: You can defer up to $23,500 of your net business income
- Employer Contribution: Up to 25% of your adjusted net business income
Adjusted net business income is calculated as:
Net Schedule C Profit
− 50% of Self-Employment Tax
− Employer Solo 401(k) Contribution (self-referential)
= Adjusted Net Business IncomeThe effective employer contribution rate works out to approximately 20% of net Schedule C profit (not 25%) because of the self-referential deduction.
LLC Solo 401(k) Example (2026)
Scenario: LLC owner with $150,000 net Schedule C profit
| Component | Calculation | Amount |
|---|---|---|
| Net Profit | Schedule C | $150,000 |
| SE Tax (approx.) | $150,000 × 92.35% × 15.3% | $21,252 |
| Deductible SE Tax (50%) | $21,252 ÷ 2 | $10,626 |
| Employee Deferral | Flat limit | $23,500 |
| Employer Contribution | ~20% of ($150,000 − $10,626 − Employer Contrib.) | ~$27,849 |
| Total Contribution | ~$51,349 |
LLC Advantages for Solo 401(k)
- Simple calculation: No payroll needed; contributions based on tax return numbers
- Full flexibility: Can adjust contributions anytime before year-end tax filing
- No payroll costs: Save $500–$2,000 annually on payroll processing
- Lower income benefits: At incomes under $80,000, LLCs can often contribute more than S Corps
LLC Disadvantages
- No W-2 salary optimization: Cannot strategically lower salary to increase contribution ratio
- SE tax still applies: Employer contribution doesn’t reduce self-employment tax
- No Mega Backdoor Roth: Difficult to implement after-tax contributions without corporate structure
Solo 401(k) for S Corp Owners
How It Works
S Corp owners wear two hats: employee and shareholder. Your Solo 401(k) contributions are split between these two roles, creating both constraints and opportunities.
Contribution Calculation
- Employee Deferral: Limited to your W-2 salary — you cannot defer more than you earn as wages
- Employer Contribution: Up to 25% of your W-2 compensation (not total business profit)
This means your salary directly controls your maximum contribution ceiling.
S Corp Solo 401(k) Example (2026)
Scenario: S Corp owner with $200,000 business profit, $120,000 W-2 salary
| Component | Calculation | Amount |
|---|---|---|
| W-2 Salary | Set by owner (must be reasonable) | $120,000 |
| Employee Deferral | $23,500 (limited to salary) | $23,500 |
| Employer Contribution | 25% × $120,000 | $30,000 |
| Total Contribution | $53,500 | |
| Remaining business profit (distributed) | $200,000 − $120,000 − $30,000 | $50,000 |
The Salary Optimization Sweet Spot
For Solo 401(k) maximization, S Corp owners should set salary at the intersection of:
- Reasonable compensation requirements (IRS scrutiny threshold)
- Maximum Solo 401(k) contribution (25% of salary + $23,500 ≤ $70,000)
- SE tax savings (lower salary = more distributions = less FICA)
To max out the full $70,000:
$23,500 (employee) + 25% of Salary = $70,000
25% of Salary = $46,500
Salary = $186,000At $186,000 W-2 salary, you can contribute the full $70,000 to your Solo 401(k).
S Corp Advantages for Solo 401(k)
- Tax-optimized contributions: Employer contribution is a corporate deduction that reduces taxable business income
- Salary control: Strategically set wages to balance contributions vs. distributions
- Lower overall tax: Distributions avoid FICA, saving ~15.3% on non-salary profit
- Clean separation: Employee and employer roles are clearly delineated
S Corp Disadvantages
- Payroll requirement: Must run actual payroll (W-2 wages), costing $500–$2,000/year
- Salary ceiling effect: If salary is set too low to save on FICA, Solo 401(k) contributions are also capped
- Reasonable compensation risk: IRS may challenge low salaries, affecting contribution validity
Solo 401(k) for C Corp Owners
How It Works
C Corporations offer a unique Solo 401(k) advantage: the ability to make after-tax contributions that can be converted to Roth — the Mega Backdoor Roth strategy.
Contribution Calculation
- Employee Deferral: Up to $23,500 from W-2 wages
- Employer Contribution: Up to 25% of W-2 compensation
- After-Tax Contribution: Up to the plan’s overall limit ($70,000 total in 2026)
C Corp Solo 401(k) Example (2026)
Scenario: C Corp owner with $250,000 salary, plan permits after-tax contributions
| Component | Calculation | Amount |
|---|---|---|
| Employee Deferral (pre-tax) | Flat limit | $23,500 |
| Employer Contribution | 25% × $250,000 | $62,500 |
| Pre-tax Subtotal | $86,000 | |
| Capped at | $70,000 | |
| Alternative: Mega Backdoor Roth | ||
| Employee Deferral | $23,500 | $23,500 |
| Employer Contribution | $0 (reduced) | $0 |
| After-Tax Contribution | $70,000 − $23,500 | $46,500 |
| Total | $70,000 | |
| → In-plan Roth Conversion | Tax-free growth | $46,500 Roth |
Mega Backdoor Roth: The C Corp Superpower
The Mega Backdoor Roth allows C Corp owners to contribute up to $46,500 in after-tax dollars beyond the standard employee deferral, then convert those funds to Roth inside the plan. This means:
- $23,500 in pre-tax or Roth employee contributions
- $46,500 in after-tax contributions (convertible to Roth)
- Total Roth balance potential: Up to $70,000 per year, growing tax-free forever
Over 20 years at 7% average returns, that’s potentially $2.8 million+ in tax-free retirement income from Mega Backdoor Roth contributions alone.
C Corp Advantages for Solo 401(k)
- Mega Backdoor Roth access: Largest Roth accumulation opportunity of any entity type
- Corporate deduction: Employer contributions reduce corporate taxable income at the 21% rate
- Flexible compensation: Can adjust salary and contributions independently
- Highest contribution ceiling: With sufficient salary, can maximize every dollar
C Corp Disadvantages
- Double taxation: Corporate profits taxed at 21%, plus personal tax on dividends/salary
- Complexity: Corporate formalities, separate tax returns, higher accounting costs
- Overkill for most small businesses: The C Corp structure makes sense primarily for high-earning owners who specifically want Mega Backdoor Roth access
Head-to-Head Comparison: Same Income, Different Entity
Scenario: $200,000 Business Net Income
| Metric | LLC (Sole Prop) | S Corp | C Corp |
|---|---|---|---|
| W-2 Salary | $0 | $120,000 | $200,000 |
| Employee Deferral | $23,500 | $23,500 | $23,500 |
| Employer Contribution | ~$37,849 | $30,000 | $46,500* |
| After-Tax (Roth) | $0 | $0 | $0 |
| Total Solo 401(k) | ~$61,349 | $53,500 | $70,000 |
| SE/FICA Tax | ~$28,336 | ~$18,360 | ~$30,600 |
| Income Tax Saved | ~$14,500 | ~$12,700 | ~$14,700 |
| Payroll Cost | $0 | ~$1,200 | ~$2,400 |
*Employer contribution reduced to keep total within $70,000 limit.
Key Insight
At $200,000 income, the LLC allows the highest pre-tax contribution (~$61,349) without payroll costs, but the S Corp saves ~$10,000 in FICA taxes. The C Corp maxes out contributions but incurs the highest overall tax burden due to double taxation.
SECURE 2.0 Changes That Affect 2026 Contributions
Roth Catch-Up Mandate
As of 2026, participants earning over $145,000 (indexed annually) in the prior year must make their catch-up contributions as Roth (after-tax) contributions. This impacts:
- S Corp and C Corp owners with salaries above $145,000: Your $7,500 catch-up must go into the Roth bucket
- LLC owners with net profits above $145,000: Same Roth catch-up requirement
- Planning impact: Reduces the immediate tax deduction for catch-up contributions but provides future tax-free growth
Enhanced Starter 401(k) Option
SECURE 2.0 introduced Starter 401(k) plans with:
- Auto-enrollment at 3% (escalating to 10%)
- No employer contributions required
- Lower administrative burden
- 2026 deferral limit: $7,000 ($8,000 if 50+)
Entity impact: Starter plans work well for LLCs that want minimal administration, but they eliminate the employer contribution bucket — significantly reducing total savings potential.
Pension-Linked Emergency Savings Accounts
New for 2026, employers can offer sidecar emergency savings accounts alongside the Solo 401(k):
- Up to $2,500 in Roth contributions
- Penalty-free withdrawals for emergencies
- Does not count against Solo 401(k) contribution limits
How to Choose the Right Entity for Solo 401(k) Maximization
Decision Framework
Choose LLC (Sole Proprietorship) if:
- Business income is under $80,000/year
- You want maximum simplicity and lowest admin costs
- You’re just starting out and not sure about long-term profitability
- You prioritize highest contribution rate at lower income levels
Choose S Corp if:
- Business income is $100,000–$500,000/year
- You want to optimize both SE tax savings and retirement contributions
- You’re comfortable with payroll processing and reasonable salary requirements
- You want the best balance of tax efficiency and contribution flexibility
Choose C Corp if:
- Business income exceeds $500,000/year
- You specifically want Mega Backdoor Roth access ($46,500+ in annual Roth conversions)
- You’re reinvesting profits into the business rather than distributing them
- You have a long-term exit strategy (QSBS exclusion planning)
Income Breakpoints
| Annual Business Income | Recommended Entity | Max Solo 401(k) | Key Reason |
|---|---|---|---|
| Under $60,000 | LLC | ~$35,000 | No payroll cost; higher effective rate |
| $60,000–$100,000 | LLC or S Corp | ~$43,000–$48,000 | Break-even zone; LLC simpler |
| $100,000–$186,000 | S Corp | $48,000–$70,000 | SE tax savings outweigh payroll costs |
| $186,000–$500,000 | S Corp | $70,000 (maxed) | Full contribution + maximum FICA savings |
| $500,000+ | C Corp | $70,000 + Mega Backdoor Roth | Roth accumulation strategy + QSBS planning |
Solo 401(k) Setup Checklist by Entity Type
For All Entity Types
- Adopt a written Solo 401(k) plan document (by December 31 of the tax year)
- Open a Solo 401(k) account at a brokerage (Fidelity, Charles Schwab, Vanguard, etc.)
- Obtain an EIN for the plan (free via IRS.gov)
- File Form 5500-EZ once plan assets exceed $250,000
LLC Additional Steps
- Calculate employer contribution using the self-employed deduction worksheet
- Ensure Schedule C net profit is sufficient for both employee and employer portions
- No payroll setup needed
S Corp Additional Steps
- Establish payroll processing for W-2 wages
- Set employee deferral through payroll withholding
- Calculate employer contribution as 25% of W-2 compensation
- Ensure salary meets reasonable compensation standards
C Corp Additional Steps
- Configure plan document to permit after-tax contributions (if pursuing Mega Backdoor Roth)
- Set up in-plan Roth conversion or in-service withdrawal feature
- Coordinate corporate tax deduction with contribution timing
Common Solo 401(k) Mistakes by Entity Type
LLC Mistakes
- Calculating 25% instead of ~20%: LLC owners often mistakenly calculate 25% of net profit instead of the effective ~20% rate after the self-referential deduction adjustment
- Forgetting SE tax deduction: Not subtracting half of SE tax before calculating employer contribution
- Missing the deadline: Employee deferrals must be elected by December 31; employer contributions can be made until tax filing deadline
S Corp Mistakes
- Setting salary too low for contributions: A $50,000 salary limits employer contribution to $12,500, capping total at $36,000 — well below the $70,000 ceiling
- Not running payroll before year-end: Employee deferrals must come from actual payroll withholding processed before December 31
- Ignoring reasonable compensation: The IRS may reclassify distributions as wages, invalidating contribution calculations
C Corp Mistakes
- Not amending plan for after-tax contributions: The default Solo 401(k) plan may not permit Mega Backdoor Roth — you must explicitly enable this feature
- Double-counting W-2 and corporate contributions: Ensure employer contributions don’t push the total over the $70,000 limit
- Forgetting Form 5500-EZ: C Corp plans are more likely to exceed the $250,000 filing threshold
Frequently Asked Questions
Can I have a Solo 401(k) if my LLC also has employees?
Yes, but the “solo” designation only applies if your only employees are you and your spouse. If you have full-time W-2 employees (other than a spouse), you must offer the 401(k) to all eligible employees under ERISA rules, which eliminates the Solo 401(k) advantage. Part-time employees working fewer than 1,000 hours/year and independent contractors don’t count.
Can I switch entity types without disrupting my Solo 401(k)?
Yes. Your Solo 401(k) plan is maintained at the plan level, not the entity level. If you convert from LLC to S Corp (or vice versa), the same plan continues — but your contribution calculation method changes. You’ll need to update your contribution strategy to match the new entity’s rules in the year of conversion.
What happens to my Solo 401(k) if the TCJA provisions expire in 2026?
The QBI deduction expiration (scheduled for tax years beginning after December 31, 2025) affects your overall tax strategy but does not directly impact Solo 401(k) contribution limits. However, the loss of the 20% QBI deduction may make the tax-deduction benefit of Solo 401(k) contributions more valuable, potentially shifting the optimal entity choice analysis.
Can I contribute to both a workplace 401(k) and a Solo 401(k)?
You can have both plans, but the $23,500 employee deferral limit is shared across all 401(k) plans. If you defer $15,000 into a workplace 401(k), you can only defer $8,500 into your Solo 401(k) as an employee. However, employer contributions are separate — you can receive the full employer contribution from your Solo 401(k) regardless of participation in another employer’s plan.
How does the Solo 401(k) interact with the Roth IRA?
Solo 401(k) contributions do not affect your ability to contribute to a Roth IRA directly. However, high earners (above IRA income limits) can use the Mega Backdoor Roth within a Solo 401(k) to get far more money into Roth treatment than a standard Roth IRA allows — $46,500+ vs. the $7,000 Roth IRA limit. The Solo 401(k) and Roth IRA are separate buckets with independent contribution limits.
Tax Deduction Impact Summary (2026)
| Entity Type | Employee Deferral Deduction | Employer Contribution Deduction | After-Tax Roth Deduction |
|---|---|---|---|
| LLC (Sole Prop) | Reduces personal AGI | Reduces personal AGI | N/A (after-tax by definition) |
| S Corp | Reduces W-2 Box 1 wages | Reduces corporate taxable income (flows to K-1) | N/A |
| C Corp | Reduces W-2 wages | Reduces corporate taxable income at 21% rate | N/A |
Next Steps: Maximize Your Retirement Strategy
- Review your entity classification: Confirm whether your LLC is taxed as sole prop, partnership, S Corp, or C Corp
- Calculate your 2026 contribution ceiling: Use the formulas above based on your entity type
- Establish or update your Solo 401(k) plan: Ensure the plan document supports all contribution types you want to use
- Set up payroll (if S Corp/C Corp): Process employee deferrals before December 31
- Make employer contributions by tax deadline: April 15, 2027 (or October 15 with extension) for the 2026 tax year
Ready to Compare Entity Types?
Use our comprehensive comparison tools to find the optimal structure for your business and retirement goals:
- LLC vs S Corp Complete Guide — Full breakdown of differences, costs, and tax implications
- Self-Employment Tax Savings by Entity — How to minimize the 15.3% SE tax burden
- S Corp Salary Optimization — Strategic salary setting for maximum tax efficiency
- TCJA Sunset: Entity Selection Impact — Prepare for expiring tax provisions in 2026
Disclaimer: This article is for informational purposes only and does not constitute tax, legal, or financial advice. Contribution limits and tax rules change annually. Consult a qualified CPA or financial advisor before making entity elections or retirement plan decisions.