Selecting a retirement plan as a high earner is a tax decision, a cash flow decision, and often a structural choice that affects how a business operates over time.
When you’re choosing between a solo 401(k), SEP IRA, and defined benefit plan, you’ll notice that each one has different contribution mechanics, administrative requirements, and long-term effects.
Knowing how they work in practice helps you evaluate trade-offs and align your choice with broader financial objectives.
Understanding Solo 401(k)s
A solo 401(k), sometimes called an individual 401(k), is designed for self-employed individuals or business owners with no employees other than a spouse.
At a high level, it combines two types of contributions:
- Employee deferrals
- Employer contributions
This structure enables higher potential contributions compared to some alternatives.
Employee contributions can be made up to the annual limit ($24,500 in 2026), with the option to contribute up to 100% of compensation, subject to that cap. Employer contributions can then be added, generally up to 25% of compensation, with a combined total limit of $72,000.
Solo 401(k)s can also be structured as either:
- Pre-tax (traditional), where taxes are deferred until withdrawal.
- Roth, where contributions are made after tax and qualified withdrawals are tax-free.
Understanding SEP IRAs
A SEP IRA (Simplified Employee Pension) allows employers, including self-employed individuals, to contribute toward retirement accounts on behalf of themselves and any eligible employees.
Unlike a solo 401(k), contributions are made solely by the employer. Contribution limits are generally capped at 25% of compensation, up to $72,000 in 2026.
At a structural level, SEP IRAs are simpler to administer. However, they introduce an important constraint: contributions must be made proportionally for all eligible employees.
For example, if a business owner contributes 5% of compensation to their own account, they are typically required to contribute the same percentage for each eligible employee.
This requirement may not be material for sole proprietors. However, as a business grows, it can considerably increase total contribution costs.
SEP IRAs generally follow traditional IRA tax treatment, including:
- Tax-deferred growth
- Ordinary income taxation on withdrawals
- Early withdrawal penalties before age 59½
- Required minimum distributions beginning at age 73
Understanding Defined Benefit Plans
Defined benefit plans differ substantially from SEP IRAs and 401(k)s.
Rather than focusing on annual contributions, these plans are structured around a targeted retirement benefit.
An actuary determines required annual contributions based on factors such as:
- Age
- Income
- Expected retirement date
For high earners, this often results in substantially higher allowable contributions. As of 2025, the maximum annual benefit limit translates to contributions that can exceed $290,000, depending on the structure of the plan.
However, this flexibility comes with additional complexity. Defined benefit plans typically require:
- Ongoing actuarial oversight
- Higher administrative costs
- Consistent annual funding
Unlike other plans, contributions are not discretionary. Once established, the plan generally requires funding each year, regardless of business performance.
As a result, these plans are most commonly used by individuals with stable, predictable income who want to accelerate retirement savings within a defined timeframe.
Key Differences in Contribution Structure
The primary distinction between each plan lies in how contributions are calculated and applied.
A solo 401(k) allows for both employee and employer contributions, enabling higher savings at lower income levels.
A SEP IRA limits contributions to a percentage of income, which can reduce flexibility for those looking to maximize contributions quickly.
A defined benefit plan shifts the focus entirely, using actuarial calculations to determine contribution levels based on a future income target.
Illustrating the Difference
Consider a self-employed individual earning $60,000.
Under a SEP IRA, contributions would generally be limited to 25% of income, or $15,000.
Under a solo 401(k), the same individual could contribute:
- Up to $23,500 as an employee, plus
- Up to $15,000 as an employer
This results in a total potential contribution of $38,500, more than double the SEP IRA contribution at the same income level.
At higher income levels, the gap may narrow due to overall contribution caps, but the structural flexibility of the solo 401(k) remains relevant.
Catch-Up Contributions
Solo 401(k) plans allow additional contributions for individuals age 50 and older. As of 2025:
- Standard catch-up contributions: $7,500
- Ages 60–63: up to $11,250
SEP IRAs and defined benefit plans do not offer comparable catch-up contribution structures in the same way.
This can make the solo 401(k) more attractive for those approaching retirement who want to increase contributions in a shorter time horizon.
Employee Considerations
Eligibility rules differ meaningfully across plans.
Solo 401(k)s are generally limited to businesses with no employees other than a spouse.
SEP IRAs and defined benefit plans, by contrast, allow for employee participation, but introduce cost-sharing requirements. For SEP IRAs, contributions must be applied equally across eligible employees.
Defined benefit plans may also require funding commitments linked to employee participation, depending on plan design.
Common Planning Considerations
Several factors frequently influence the decision between these plans:
- Income variability: Plans with flexible contribution structures may be more appropriate for individuals with fluctuating income.
- Administrative complexity: Defined benefit plans require significantly more oversight than SEP IRAs or solo 401(k)s.
- Employee presence: Hiring employees can limit the practicality of a solo 401(k) and increase costs under other plans.
- Contribution goals: Those seeking to maximize contributions quickly may benefit from the structure of a solo 401(k) or defined benefit plan.
- Cash flow stability: Required contributions under defined benefit plans may not align with inconsistent business income.
Final Thoughts
Choosing between a solo 401(k), SEP IRA, and defined benefit plan is less about selecting the “best” option and more about selecting the most appropriate structure.
Each plan carries different implications for taxes, cash flow, administrative burden, and long-term flexibility.
In many cases, the right choice is the one that balances contribution potential with sustainability, so you can support both current operations and long-term financial goals.
Disclaimer: There is no guarantee that a diversified portfolio will enhance overall returns or outperform a non-diversified portfolio. Diversification does not protect against market risk. Content in this material is for general information only and is not intended to provide specific advice or recommendations for any individual. All investing involves risk, including loss of principal. No strategy ensures success or protects against loss.
