Retirement Plan Strategies for S-Corp Owners: Solo 401(k), SEP IRA, and Defined Benefit Plans

For S-Corp owners generating strong cash flow, one of the most powerful tax reduction strategies available has nothing to do with deductions or entity restructuring. It involves choosing the right retirement plan. The Internal Revenue Code provides several qualified plan structures that allow business owners to shelter significant income from current taxation, and when these plans are paired with an S-Corp's compensation framework, the results can be transformative.

Unlike sole proprietors or partners, S-Corp shareholders who work in the business must pay themselves a reasonable salary under IRC Section 1366. That salary becomes the basis for calculating both employee elective deferrals and employer profit-sharing contributions. Getting compensation right is essential before evaluating which plan to adopt, because the wrong salary level can cap your contributions too low or create unnecessary payroll tax exposure.

The Solo 401(k): Maximum Flexibility for Owner-Only Businesses

The Solo 401(k), also referred to as an individual 401(k), is available to businesses with no full-time employees other than the owner and spouse. Under IRC Section 401(k), the plan allows both an employee elective deferral and an employer profit-sharing contribution. For 2026, the employee deferral limit is $23,500, with an additional $7,500 catch-up contribution for those age 50 and older. The S-Corp can also make an employer contribution of up to 25% of the owner's W-2 compensation, subject to the overall annual addition limit of $70,000 under IRC Section 415(c) (or $77,500 including catch-up contributions).

An owner paying themselves a W-2 salary of $200,000 could defer $23,500 as the employee, then have the corporation contribute an additional $50,000 as a 25% employer match, for a total of $73,500 in tax-deferred savings. The employee deferral portion can even be designated as Roth under IRC Section 402A, allowing tax-free growth on a portion of the contribution while still capturing a current deduction on the employer side. The Solo 401(k) also permits participant loans of up to $50,000 or 50% of the vested balance under IRC Section 72(p), a liquidity feature unavailable in SEP IRAs.

The SEP IRA: Simplicity with a Significant Trade-Off

The Simplified Employee Pension (SEP) IRA, governed by IRC Section 408(k), is one of the easiest retirement plans to establish and administer. There is no annual IRS filing requirement, no discrimination testing, and setup can be completed with a single form. For S-Corp owners, the contribution limit is 25% of W-2 compensation, up to the overall cap of $70,000 for 2026.

However, the simplicity of the SEP comes with a notable constraint. Unlike the Solo 401(k), the SEP IRA does not allow employee elective deferrals. All contributions are employer contributions only. This means an S-Corp owner paying themselves a salary of $200,000 is limited to a $50,000 contribution, compared to the $73,500 or more available through a Solo 401(k). For owners with compensation below $280,000, the Solo 401(k) will almost always produce a higher allowable contribution than the SEP.

The SEP also creates complications when a business has additional employees. Under IRC Section 408(k)(2), any employee who has worked for the employer in at least three of the preceding five years and has earned at least $750 must be included in the plan. Contributions must be made at the same percentage of compensation for all eligible employees, which can significantly increase plan costs for businesses with staff beyond the owner.

Defined Benefit and Cash Balance Plans: Supercharging Contributions

For S-Corp owners with consistently high income who want to shelter far more than $70,000 per year, defined benefit plans and cash balance plans offer dramatically higher contribution limits. Under IRC Section 415(b), a defined benefit plan can fund an annual retirement benefit of up to $280,000 per year at retirement age. Depending on the owner's age and years to retirement, this can translate into annual deductible contributions of $150,000 to $350,000 or more.

Cash balance plans are a hybrid structure that functions as a defined benefit plan for regulatory and tax purposes but provides each participant with an individual account balance. The actuarial calculations required under IRC Section 412 determine the deductible contribution each year, and because the benefit is guaranteed by the plan sponsor, contributions are mandatory once the plan is established.

Many S-Corp owners layer a cash balance plan on top of a Solo 401(k) to maximize total contributions. An owner age 55 with a $250,000 salary might contribute $77,500 through the Solo 401(k) and an additional $200,000 through the cash balance plan, sheltering $277,500 from current income tax in a single year. The administrative costs are higher (typically $2,000 to $5,000 annually), but those costs are themselves deductible and are trivial relative to the tax savings generated.

The Mega Backdoor Roth Strategy

For S-Corp owners who want to build tax-free retirement wealth, the mega backdoor Roth strategy provides an opportunity that goes well beyond the standard Roth IRA contribution limits. Under IRC Section 415(c), the total annual addition limit for a defined contribution plan is $70,000 for 2026. After accounting for the employee elective deferral ($23,500) and the employer profit-sharing contribution (25% of compensation), any remaining room under the $70,000 cap can be filled with after-tax employee contributions, provided the plan document allows them.

Those after-tax contributions can then be converted to a Roth account, either within the plan through an in-plan Roth conversion or by rolling them out to a Roth IRA. Because the contributions were made with after-tax dollars, only the earnings (if any) are taxable upon conversion. This strategy can allow an S-Corp owner to funnel $20,000 to $40,000 or more per year into Roth accounts, far exceeding the standard $7,000 Roth IRA contribution limit. Implementing the mega backdoor Roth requires that the Solo 401(k) plan document explicitly permit after-tax contributions and in-service distributions. Not all prototype documents include these provisions, so working with an experienced plan administrator is essential. Attention to the pro-rata rule under IRC Section 72(e) and proper ordering of conversions will minimize tax on accumulated earnings.

Choosing the Right Structure for Your S-Corp

The right retirement plan depends on several interconnected factors: your current W-2 compensation level, your age, how many years remain until your target retirement date, whether you have employees, and how much cash flow you can commit to annual contributions. Younger S-Corp owners with moderate income may find the Solo 401(k) provides the best combination of flexibility and contribution capacity. Owners in their late 40s and 50s with high and stable income should seriously evaluate adding a cash balance plan to capture six-figure annual deductions during their peak earning years.

The compensation planning aspect cannot be overlooked. Because S-Corp retirement contributions are calculated based on W-2 salary, the reasonable compensation analysis under IRC Section 1366 directly affects how much you can contribute. Setting your salary too low to minimize payroll taxes may inadvertently limit your retirement plan contributions and cost you far more in lost tax-deferred savings than you gained in FICA reduction. Additionally, retirement plan contributions reduce your qualified business income for purposes of the IRC Section 199A deduction. For S-Corp owners who qualify for the 20% pass-through deduction, the interaction between retirement plan contributions and the QBI deduction must be modeled carefully, though the net tax benefit of the contribution almost always remains strongly positive.

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This article is for informational purposes only and does not constitute legal or tax advice. Consult a qualified tax professional regarding your specific circumstances. AE Tax Advisors, 935 Lake Elmo Dr, Suite B, Billings, MT 59105. Phone: (631) 614-5762.