S-Corp Solopreneurs: Compare Solo 401k vs SEP IRA

Watch: Why the Solo 401k crushes the SEP IRA for S-Corp solopreneurs — contribution limits, Mega Backdoor Roth, catch-up rules, and more

If you’re an S-Corp solopreneur — meaning you own an S-Corporation, take W-2 wages from it, and have no full-time non-owner, non-spouse W-2 employees — you have two primary retirement plan options: the Solo 401k and the SEP IRA. On the surface they look similar, but dig a little deeper and the Solo 401k wins in virtually every meaningful category.

Solo 401k vs SEP IRA: At-a-Glance Comparison for S-Corp Solopreneurs

Both the Solo 401k and the SEP IRA share the same headline annual contribution ceiling — $70,000 in 2025 and $72,000 in 2026 — but that surface-level parity disappears quickly once you examine the structure, flexibility, and tax advantages each plan actually delivers.

Feature	Solo 401k	SEP IRA
2026 Base Contribution Limit	$72,000	$72,000
Contribution Buckets	Employee Deferral + Employer + Voluntary After-Tax	Employer Only
Mega Backdoor Roth Available	✅ Yes	❌ No
Roth Employee Contributions	✅ Yes	❌ No
Catch-Up (Age 50+, 2026)	$8,000 additional	❌ No
Super Catch-Up (Age 60–63, 2026)	$11,250 additional	❌ No
SECURE Act Tax Credit	✅ Up to $1,500	❌ No
Participant Loan Provision	✅ Yes	❌ No
Income Limits for Mega Backdoor Roth Contributions	❌ None	N/A
W-2 Wages Needed to Maximize	$72,000 (Mega Backdoor Roth)	$288,000

Who Qualifies? Eligibility for S-Corp Solopreneurs

To be eligible for either plan as an S-Corp solopreneur, you must meet two key criteria:

No full-time, non-owner, non-spouse W-2 employees working for any business you or your spouse own.
Earned self-employment income — for S-Corp owners, this means receiving W-2 wages from the S-Corporation, which is how earned income is demonstrated for plan contribution purposes.

📋 Example: Maria operates a consulting firm as a single-member S-Corporation. She pays herself $80,000 in W-2 wages for 2026 and has no other employees. Maria is eligible for both the Solo 401k and the SEP IRA — but as you’ll see below, the Solo 401k will allow Maria to put far more into tax-advantaged retirement accounts and with far less income required to do so.

Reason #1: Mega Backdoor Roth — Exclusive to the Solo 401k

Perhaps the single greatest advantage of the Solo 401k for S-Corp solopreneurs is the ability to execute the Mega Backdoor Roth strategy. This is simply not possible with a SEP IRA.

How the Mega Backdoor Roth Works

The Mega Backdoor Roth is a two-step process that allows solopreneurs to contribute after-tax dollars to their Solo 401k and then convert those funds to a Roth account — either a Roth Solo 401k or a Roth IRA:

Step 1: Make voluntary after-tax contributions to the Solo 401k (up to $72,000 for 2026).
Step 2: Transfer (convert) those after-tax dollars to a Roth Solo 401k or a Roth IRA where they grow tax-free.

📋 Example: Alex is an S-Corp solopreneur paying himself $72,000 in W-2 wages in 2026. Alex uses the Mega Backdoor Roth strategy to contribute the full $72,000 as voluntary after-tax contributions to his Solo 401k, then converts them to his Roth Solo 401k. That’s nearly 10× what a direct Roth IRA contribution would allow — and with no income limits restricting his ability to contribute.

Why the SEP IRA Can’t Do This

The SEP IRA only accepts employer contributions. Voluntary after-tax contributions — the foundation of the Mega Backdoor Roth — are simply not permitted in a SEP IRA. This alone is a decisive reason to choose the Solo 401k.

⚠️ Important: Not all Solo 401k plan documents allow voluntary after-tax contributions. You need a plan specifically designed to include this feature — such as the plan offered by My Solo 401k Financial. Without the right plan document, the Mega Backdoor Roth strategy is off the table even if you have a Solo 401k.

Additionally, unlike a Roth IRA, which phases out for high earners, the Mega Backdoor Roth Solo 401k has no income limits. High-earning S-Corp solopreneurs can take full advantage regardless of their income level.

Reason #2: Contribution Velocity — Maximize With Lower W-2 Wages

One of the most underappreciated advantages of the Solo 401k for S-Corp owners is contribution velocity — the ability to reach the annual maximum contribution with significantly lower W-2 wages than a SEP IRA requires.

The SEP IRA Math: $288,000 Needed to Max Out

The SEP IRA employer contribution limit is 25% of W-2 wages. To reach the 2026 maximum of $72,000 through a SEP IRA, an S-Corp solopreneur would need to pay themselves $288,000 in W-2 wages ($288,000 × 25% = $72,000). Higher W-2 wages may also mean higher Social Security and Medicare (FICA) taxes — an added cost often overlooked in the SEP IRA calculation.

The Solo 401k Math: $72,000 Is Enough for a Full Mega Backdoor Roth

With a Solo 401k and the Mega Backdoor Roth strategy, an S-Corp solopreneur needs only $72,000 in W-2 wages to make the full $72,000 voluntary after-tax contribution. That’s one-quarter of the W-2 wages the SEP IRA path would require.

💡 Key Insight: By keeping W-2 wages lower while still maximizing retirement contributions via the Mega Backdoor Roth, S-Corp solopreneurs may be able to reduce Social Security and Medicare taxes while still building substantial tax-advantaged wealth — a dual benefit unavailable through the SEP IRA.

Reason #3: Catch-Up & Super Catch-Up Contributions (Age 50+)

Catch-up and super catch-up contributions are employee contribution types — and since the SEP IRA only allows employer contributions, these higher limits are simply unavailable to SEP IRA holders. The Solo 401k unlocks both.

Standard Catch-Up (Age 50+)

For 2026, if you are age 50 or older, you can make an additional employee catch-up contribution of $8,000 — raising your total potential Solo 401k contribution from $72,000 to $80,000.

Super Catch-Up (Age 60–63)

Introduced under the SECURE Act, the super catch-up contribution allows solopreneurs who are age 60 to 63 (as of December 31, 2026) to contribute an even larger catch-up amount. For 2026, the super catch-up is $11,250 — bringing the total potential Solo 401k contribution to $83,250.

Age Group	Solo 401k (2026)	SEP IRA (2026)
Under Age 50	$72,000	$72,000
Age 50–59 or 64+	$80,000 (+$8,000 catch-up)	$72,000 — no catch-up
Age 60–63	$83,250 (+$11,250 super catch-up)	$72,000 — no catch-up

Reason #4: SECURE Act Tax Credits — Up to $1,500 for Solo 401k Owners

The SECURE Act introduced a small business retirement plan startup tax credit, and My Solo 401k Financial is proud to be the first Solo 401k provider offering a plan that qualifies solopreneurs to claim this credit. SEP IRA holders are not eligible for this specific credit.

How the Tax Credit Works

$500 per year for three consecutive years = $1,500 total
This is a tax credit, not a deduction — meaning it’s a dollar-for-dollar reduction in your tax liability
The plan must include an automatic enrollment feature to qualify
The credit applies to qualifying new Solo 401k plans as well as existing plans that are upgraded to include the feature

💡 Why It Matters: The $1,500 tax credit more than covers My Solo 401k Financial’s fees for the first seven years. The fee structure is straightforward: a one-time $650 initial fee (which includes a $525 establishment fee plus the first year’s $125 annual fee), then a flat $125 annual fee each year thereafter.

⚠️ Important: The SECURE Act tax credit for new retirement plans requires an automatic enrollment feature. Not all Solo 401k plan documents include this. The Solo 401k plan offered by My Solo 401k Financial is specifically designed to qualify for this credit.

Reason #5: Participant Loan Provision

The Solo 401k allows participants to borrow from their own retirement funds through a participant loan. The SEP IRA offers no such feature.

Borrow up to 50% of your vested account balance or $50,000, whichever is less
Loan repayment goes back into your own account — you pay interest to yourself
Useful for short-term liquidity needs without triggering a taxable distribution

📋 Example: Carlos has $200,000 in his Solo 401k. He needs $50,000 to bridge a gap in his business cash flow. With his Solo 401k, he can take a participant loan of $50,000 — repaying himself with interest over up to five years. A SEP IRA holder in the same situation would face a taxable distribution with potential penalties if under age 59½.

Ready to Open Your Solo 401k?

Whether you’re a new S-Corp solopreneur or looking to upgrade from a SEP IRA, My Solo 401k Financial can help you set up the right Solo 401k structure — including Mega Backdoor Roth and the SECURE Act tax credit.

Next Steps: Get Started Today!

Remember: This information is provided for educational purposes only. Always consult with qualified tax, legal, and investment professionals before making decisions regarding your retirement plan.