Compares maximum retirement contribution limits between a Solo 401(k) and a SEP IRA for self-employed professionals and 1099 consultants. For example, on a $120,000 net business profit, a Solo 401(k) allows you to contribute up to $53,000 (employee + employer split), whereas a SEP IRA caps your contribution at only $24,000.
Solo 401(k) vs. SEP IRA Contribution Calculator
Maximize your tax-deferred retirement shelter as an S-Corp Owner, 1099 Contractor, or Solo Consultant.
Business & Income Profile
Employer profit sharing is calculated as 25% of this W-2 figure.
Adjusted for 50% self-employment tax deduction (20% effective rate).
Combined Federal + State tax bracket to estimate upfront cash savings.
Solo 401(k)
SEP IRA
Solo 401(k) Extra Annual Tax Shield Advantage
You can shield an additional $23,000 / year more in a Solo 401(k) than in a SEP IRA at this salary.
Projected Compounded Retirement Wealth
Solo 401(k) vs. SEP IRA compounding over your investment horizon.
Projected Solo 401(k) Nest Egg
$2,624,592
Projected SEP IRA Nest Egg
$1,485,996
Plan Architecture & Feature Breakdown
| Feature | Solo 401(k) | SEP IRA |
|---|---|---|
| Employee Contribution Allowed? | Yes (Up to $23,000 / $30,500) | No ($0) |
| Roth (Post-Tax) Option? | Yes (Roth Solo 401k + Mega Backdoor) | Limited (SECURE 2.0 partial) |
| Participant Loan Provision? | Yes (Borrow up to $50,000) | No (Prohibited transaction) |
| Backdoor Roth Compatibility | 100% Clean (No Pro-Rata Rule) | Triggers IRA Pro-Rata Rule |
| Annual IRS Filing | Form 5500-EZ (Only once assets > $250k) | None Required |
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The 1099 S-Corp Dilemma: How a Solo 401(k) Unlocked $69,000 in Deductions vs. $30,000 in a SEP IRA
A real-world tax optimization breakdown for solo consultants, developers, and agency owners balancing reasonable W-2 salaries against maximum tax shelters.
The "Two Hats" Tax Superpower
In a SEP IRA, you are strictly limited to employer contributions capped at 25% of W-2 compensation. In a Solo 401(k), an owner-operator wears two distinct hats: (1) As the Employee, you can defer up to $23,500 of salary, and (2) As the Employer, your company contributes an additional 25% of salary—enabling you to reach the maximum $69,000 IRS annual cap on a vastly lower W-2 payroll!
The Scenario: Marcus's $220,000 Software Consultancy
Marcus is a solo software architect operating as an S-Corp in Austin, Texas. His business generates $220,000 in net profit. To minimize 15.3% FICA self-employment taxes, his CPA sets a reasonable W-2 salary of $120,000, taking the remaining $100,000 as distributions. He evaluates a SEP IRA against a Solo 401(k):
Employer 25%: $30,000
Employee Deferral: $0 (Not Allowed)
Total Shelter: $30,000 / yr
Employee Deferral: $23,500
Employer Profit Share: $30,000
Total Shelter: $53,500 / yr (+$23.5k!)
Extra Pre-Tax Shield: $23,500
At 37% Combined Tax Rate:
+$8,695 Cash in Pocket Annually!
Salary Requirement to Max Out Retirement Shelters
| Plan Type | Max 2026 Limit | Required W-2 Salary | Backdoor Roth Clean? | Annual FICA Drag |
|---|---|---|---|---|
| Traditional SEP IRA | $69,000 | $276,000 | No (Pro-Rata Trap) | $20,000+ extra FICA tax |
| Solo 401(k) (Standard) | $53,500 | $120,000 | 100% Clean Exemption | $0.00 extra FICA drag |
| Solo 401(k) + Mega Backdoor Roth | $69,000 (Maxed) | $120,000 | 100% Clean Exemption | $0.00 extra FICA drag |
The Pro-Rata Backdoor Advantage
Additionally, having a pre-tax balance in a SEP IRA poisons your ability to perform annual Backdoor Roth IRA conversions due to the IRS Form 8606 Pro-Rata Rule. Because a Solo 401(k) is a 401(a) trust (not an IRA), it is 100% invisible to the pro-rata rule, allowing high earners to execute friction-free Backdoor Roths every single year!
Frequently Asked Questions (Solo 401k vs SEP IRA)
Why does a Solo 401(k) allow higher contributions than a SEP IRA on lower salaries?
A Solo 401(k) allows both an employee elective deferral ($23,500 in 2026) and a 25% employer profit-sharing contribution. A SEP IRA only allows employer contributions (25% of W-2), meaning you need a $276,000 salary to max out a SEP IRA, compared to only ~$182,000 for a Solo 401(k).
Does a Solo 401(k) trigger the IRA Pro-Rata Rule for Backdoor Roth IRAs?
No. Solo 401(k) balances are held under a qualified employer trust (IRC § 401a) and are completely exempt from the IRS Form 8606 Pro-Rata Rule, allowing you to execute clean Backdoor Roth IRAs. SEP IRAs, however, count toward your pre-tax IRA balance and trigger severe pro-rata taxes.
When is an annual IRS Form 5500-EZ required for a Solo 401(k)?
Form 5500-EZ is only required once your total Solo 401(k) plan assets (including rollover accounts and spouse assets) exceed $250,000 at the end of the plan year, or upon final plan termination.