Solo 401(k) Plans for Owner-Operators

A solo 401(k), sometimes called an individual 401(k), is a 401(k) plan covering an owner and, if applicable, a spouse who works in the business. It is not a separate type of plan under the law. It is an ordinary 401(k) that happens to have no common-law employees other than the owner and spouse, which lets the owner avoid many of the testing and administration burdens that come with larger plans.

The Two Contribution Buckets

The plan allows contributions in two capacities:

• Employee deferrals. You can elect to defer a portion of your compensation, up to an annual limit that is indexed for inflation. Those over a certain age may make additional catch-up contributions, and recent legislation increased the catch-up amount for certain ages.
• Employer contributions. The business can make a profit-sharing contribution, generally limited to a percentage of compensation. For a self-employed owner, the percentage calculation uses a modified definition of earnings that adjusts for self-employment tax, so the effective rate is lower than the headline percentage.

An overall annual limit caps the combined employee and employer contributions. The specific dollar limits change each year, so confirm current figures when planning.

Effect of Entity Type

For an S corporation owner, compensation for plan purposes is generally W-2 wages. Employee deferrals must come out of wages, so a very low salary limits how much you can defer. The employer contribution is a percentage of W-2 wages, not of distributions. For a sole proprietor or single-member LLC owner taxed as a sole proprietor, the calculation is based on net earnings from self-employment.

This is why salary planning and retirement planning interact. A modest increase in salary can support a materially higher contribution in some cases, although it also increases payroll tax. See Salary vs Distributions: Planning the Owner Pay Mix.

Roth Options

Many solo 401(k) plans offer a Roth deferral option, allowing you to make after-tax contributions that may grow tax-free if qualified distribution rules are met. Some plans also permit in-plan Roth conversions of after-tax or pre-tax balances. Availability depends on the plan document, and the tax consequences can be significant, so model them first. See Roth Conversions and Backdoor Roth Planning for Owners.

Setting Up the Plan

Setup usually involves choosing a provider, adopting a plan document, and opening an account. Deferral elections are generally made before the year end in which the compensation is earned, with special rules for certain sole proprietors. Employer contributions can generally be made up to the tax filing deadline including extensions, though details depend on your entity type. Confirm dates with your provider.

Ongoing Compliance

Solo 401(k) plans are generally exempt from many of the nondiscrimination tests that apply to larger plans, but there are still obligations:

• When plan assets exceed a threshold at the end of a plan year, an annual information return is generally required.
• Contributions must not exceed the applicable limits.
• Prohibited transactions, such as certain loans or dealings with disqualified persons, can jeopardize the plan.
• If you hire employees who become eligible, you may need to revisit the plan and cover them.

Plan Loans and Investments

Some solo 401(k) plans permit participant loans up to statutory limits, and some allow a wider range of investments than typical employer plans. These features can be attractive, but they come with technical rules. Investments in real estate or private ventures may create prohibited transaction risks or unrelated business taxable income. Discuss any unusual investment with a qualified advisor before proceeding.

A Hypothetical Illustration

Consider an owner of an S corporation with no employees who pays a salary of 100,000 dollars. The owner could defer part of that salary as an employee contribution and the company could make a profit-sharing contribution as a percentage of the 100,000 wages, up to the plan limits. The combined contribution reduces the wages subject to income tax, and the company deduction for the employer portion reduces pass-through income. The precise numbers depend on current limits and plan design, so this example is meant only to show how salary drives the calculation.

Who May Prefer Something Else

An owner with employees may not be eligible. An owner who wants larger deductions than 401(k) limits allow may look at defined benefit or cash balance plans. An owner who wants minimal administration may find a SEP IRA sufficient. See SEP IRA vs Solo 401(k) vs SIMPLE IRA for comparisons.

Read Retirement Plans for Business Owners: An Overview for an overview of alternatives.

Common Mistakes to Avoid

Owners sometimes contribute more than the limits allow because they treat the employee and employer pieces separately. Others forget that deferrals must be set up before year end, or they miss the annual filing once assets grow. Some hire a part-time employee and continue contributing as though the plan were still solo, without checking whether the new worker must be covered. A simple annual checklist that confirms compensation, contribution totals, filing status, and employee status avoids most of these problems.

Keeping Records

Retain the plan document, adoption agreement, contribution records, and account statements. A clear file makes it easier to answer questions from a provider, a lender, or an examiner.

Educational purposes only. This page is general education and is not tax, legal, or accounting advice. Tax laws change and outcomes depend on individual facts, so consult a qualified professional before acting. No result is guaranteed.