Defined Benefit Plan vs. Solo 401(k): Which Retirement Plan Is Best for Business Owners?

For self-employed business owners and high-income professionals, choosing the right retirement plan is one of the most consequential tax decisions you can make. The difference between a basic retirement vehicle and an optimized plan structure can mean tens of thousands of dollars in annual tax savings, compounding over decades into a significantly larger retirement balance.

Two plans dominate the conversation for business owners without employees (or with very few employees): the solo 401(k) and the defined benefit plan. Each has distinct contribution limits, tax advantages, administration requirements, and ideal use cases. This guide breaks down both options with concrete numbers, a side-by-side comparison, and guidance on when combining them delivers the maximum benefit.

Solo 401(k): The Flexible Foundation

The solo 401(k), also known as an individual 401(k) or one-participant 401(k), is a retirement plan designed for self-employed individuals and business owners with no full-time employees other than a spouse. It offers two types of contributions:

Employee deferrals: Up to $23,500 for 2026. This is the same limit that applies to traditional 401(k) plans at large employers.

Employer profit-sharing contributions: Up to 25% of net self-employment income (after the self-employment tax deduction) for sole proprietors, or 25% of W-2 compensation for S-Corp and C-Corp owners.

Total combined limit: $70,000 for 2026 (employee + employer contributions combined).

Catch-up contributions: Participants age 50 and older can add $7,500, bringing the total to $77,500. Participants age 60 to 63 qualify for the enhanced catch-up provision of $11,250, for a total of $81,250.

Roth option: Many solo 401(k) providers allow Roth contributions, where the employee deferral portion is made with after-tax dollars and grows tax-free.

The solo 401(k) is popular because it is inexpensive to set up, easy to administer, and offers significant flexibility. No annual filing with the IRS is required until plan assets exceed $250,000, at which point the simple Form 5500-EZ is due.

Defined Benefit Plan: The High-Deduction Powerhouse

A defined benefit plan is a traditional pension-style retirement plan that promises a specific annual benefit at retirement age. Instead of defining how much you contribute each year (as with a 401(k)), a defined benefit plan defines how much you will receive each year in retirement, and then calculates backward to determine the contributions needed to fund that benefit.

Maximum annual benefit: $275,000 per year at retirement (2026 limit). This is the benefit amount, not the contribution amount.

Annual contribution range: Contributions are determined by actuarial calculations based on your current age, planned retirement age, investment return assumptions, and the target benefit. For business owners in their late 40s to late 50s, annual contributions typically range from $100,000 to $250,000 or more.

Age-based advantage: The closer you are to retirement, the larger the required annual contribution, because there are fewer years for the money to grow. This makes defined benefit plans especially powerful for business owners age 45 and older who want to shelter large amounts of income.

Mandatory funding: Unlike a 401(k) where contributions are discretionary, defined benefit plans require minimum annual contributions based on the actuarial funding schedule. This commitment is an important consideration, as income must be sufficient and consistent enough to support the required contributions.

Side-by-Side Comparison

Feature	Solo 401(k)	Defined Benefit Plan
2026 Max Contribution	$70,000 ($77,500 to $81,250 with catch-up)	$100,000 to $250,000+ (actuarially determined)
Contribution Type	Defined contribution (you set the amount)	Defined benefit (actuary sets the amount)
Contribution Flexibility	Fully discretionary each year	Minimum annual contribution required
Age Advantage	Same limits regardless of age (except catch-up)	Higher contributions allowed for older participants
Ideal Income Range	$75,000 to $400,000+	$300,000+ (consistent income)
Setup Cost	$0 to $500	$1,500 to $3,000
Annual Admin Cost	$0 to $500	$2,000 to $5,000
Roth Option	Available (employee deferrals)	Not available
Loan Provision	Available (up to $50,000)	Generally not available
Best For	Broad range of incomes, flexible needs	High-income owners age 45+, seeking max deduction

Cash Balance Plans: The Modern Defined Benefit

Many business owners who explore defined benefit plans end up choosing a cash balance plan, which is a specific type of defined benefit plan with a more modern structure. Instead of promising a monthly pension amount, a cash balance plan credits each participant's hypothetical account with an annual pay credit (a fixed dollar amount or percentage of compensation) plus an annual interest credit (a guaranteed rate of return).

From a contribution and deduction standpoint, cash balance plans offer the same high limits as traditional defined benefit plans. The key advantages of the cash balance structure include:

Portability: When the plan terminates or a participant leaves, the balance can be rolled over to an IRA, making it easier to access and manage.

Transparency: Participants can see a clear account balance rather than a projected future pension amount, making the plan easier to understand and track.

Flexibility in design: Actuaries can design cash balance plans with varying pay credit formulas to match the business owner's income and deduction goals.

Combining Plans: The Maximum Deduction Strategy

The most powerful retirement plan strategy for high-income business owners is combining a solo 401(k) with a defined benefit or cash balance plan. Because the two plans are governed by different sections of the tax code (IRC Section 401(a) for the 401(k) and IRC Section 401(a) for the defined benefit plan, with separate contribution limits under IRC Section 415), both can operate simultaneously for the same business.

Here is what the combined strategy looks like for a 52-year-old business owner earning $500,000:

Solo 401(k) contribution: $23,500 employee deferral + $46,500 employer contribution = $70,000

Defined benefit plan contribution: Approximately $175,000 (actuarially determined based on age and benefit target)

Total annual tax-deductible contribution: $245,000

At a 37% marginal federal rate, that $245,000 deduction produces approximately $90,650 in federal tax savings in a single year. Over ten years of consistent contributions, the strategy shelters $2,450,000 from current taxation while building a substantial retirement portfolio.

Income Thresholds and Practical Considerations

Retirement plan selection should be based on several factors beyond contribution limits:

Income consistency: Defined benefit plans require minimum annual contributions. If your income fluctuates significantly from year to year, the mandatory contribution in a down year could create cash flow pressure. Business owners with variable income should consider this carefully and may want to set the target benefit conservatively.

Number of employees: Both solo 401(k) plans and defined benefit plans work best for businesses with no employees (or only a spouse as an employee). Adding employees to a defined benefit plan can significantly increase costs, because contributions may be required for eligible employees under the plan's nondiscrimination testing.

Time horizon: Defined benefit plans are most advantageous when maintained for at least 5 to 10 years. Short-term plans (less than three years) may raise IRS scrutiny and reduce the actuarial benefit.

Exit strategy: When you are ready to wind down the plan, defined benefit plan termination requires distributing benefits to participants and filing Form 5310 or a similar notice with the IRS. This process takes planning, so coordinate with your advisor well in advance of your intended termination date.

Choosing the Right Plan for Your Situation

If your net self-employment income is under $300,000 and you want simplicity and flexibility, a solo 401(k) is likely the right starting point. It provides meaningful tax deductions with minimal administrative burden.

If your income consistently exceeds $300,000 and you want to shelter more than the solo 401(k) allows, adding a defined benefit or cash balance plan on top of the 401(k) unlocks the highest possible deductions available under current tax law.

If you are age 50 or older with high income and want to accelerate retirement savings, the defined benefit plan becomes especially attractive because the actuarial calculations allow larger annual contributions for older participants.

At AE Tax Advisors, we work with business owners to model multiple retirement plan scenarios, compare the tax impact of each option, and implement the plan structure that maximizes both current-year deductions and long-term wealth accumulation. Schedule a discovery call to see which plan configuration fits your income and goals.

---

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.

Frequently Asked Questions