Can an S Corp Have a Solo 401(k)? Contributions and Deadlines

Yes, an S corporation can sponsor a Solo 401(k), and for an owner-only S corp it is usually the most powerful retirement plan available. The key rule to understand up front: every dollar you contribute to an S corp Solo 401(k) is calculated from your W-2 wages, not from the company’s profits or your shareholder distributions. For 2026, that math can push total contributions to $72,000, or up to $83,250 if you are between ages 60 and 63.¹

Why Contributions Start With Your W-2

The IRS treats an S corporation officer who performs services for the corporation as an employee, so the corporation pays you a salary and issues a W-2.² That W-2 salary is the only number that feeds your Solo 401(k). Shareholder distributions do not count. Total company profit does not count. If you pay yourself $100,000 on a W-2 and take another $80,000 in distributions, your plan math starts from $100,000.

Pre-tax elective deferrals lower the federal income tax withheld from your paycheck, but they do not reduce Social Security and Medicare taxes. The full pre-deferral salary lands in Boxes 3 and 5 of your W-2 and is subject to FICA.³ Employer profit-sharing contributions, however, escape FICA entirely and are deductible by the corporation.

Who Qualifies

The IRS calls this a “one-participant” plan for a reason: it covers only the business owner and, where applicable, a spouse who also works in the business.⁴ The plan works as long as no one outside that circle becomes eligible for coverage.

The threshold is 1,000 hours of service in a year. A part-time contractor or a seasonal hire who stays under that mark does not disqualify the plan. Once a common-law employee hits 1,000 hours, they become eligible, and you can no longer maintain a Solo 401(k). Some plans also require coverage for employees who complete three consecutive years of at least 500 hours each, a rule added by the SECURE Act.⁵

If you plan to hire, timing matters. Bringing on a full-time employee mid-year does not retroactively void contributions already made, but you will need to either terminate the Solo 401(k) and roll assets into another vehicle, or convert it to a standard 401(k) with nondiscrimination testing.⁶

How Much You Can Contribute in 2026

Your total contribution has two parts, both calculated from W-2 wages. The combined ceiling is $72,000 before any catch-up.¹

Employee Elective Deferral

As the employee, you can defer up to $24,500 of your W-2 compensation in 2026.⁷ At age 50 or older, you can add an $8,000 catch-up, for a maximum deferral of $32,500. Between ages 60 and 63, a SECURE 2.0 provision raises that catch-up to $11,250, pushing your maximum deferral to $35,750.¹

You can make the deferral pre-tax or as a Roth contribution. SECURE 2.0 also lets plans allow the employer profit-sharing side to be designated as Roth, though not every plan document has been updated to permit this.⁸

One boundary worth flagging: the $24,500 limit is per person, not per plan. If you also participate in another employer’s 401(k) through a day job, your combined deferrals across all plans cannot exceed $24,500 (plus any applicable catch-up). Going over creates a double-taxation problem on the excess.⁹

Employer Profit-Sharing Contribution

The S corp, acting as employer, can contribute up to 25% of your W-2 compensation as a profit-sharing contribution.⁴ This sits on top of your employee deferral, but the two combined cannot exceed $72,000 before catch-ups.

The compensation used in that 25% calculation is capped at $360,000 for 2026.¹ But for most owners, the practical target salary for maxing out is much lower. At a W-2 of about $190,000, the employer contribution alone reaches $47,500, which combined with the $24,500 deferral hits the $72,000 ceiling exactly.

The Numbers in Practice

An S corp owner under age 50 with a 2026 W-2 salary of $190,000:

Employee deferral: $24,500
Employer profit-sharing: 25% × $190,000 = $47,500
Total: $72,000

Same owner at age 62, eligible for the enhanced SECURE 2.0 catch-up:

Employee deferral: $24,500 + $11,250 = $35,750
Employer profit-sharing: $47,500
Total: $83,250

Catch-up contributions sit on top of the $72,000 ceiling, so they do not eat into the employer contribution.¹

Setting a Salary That Holds Up

Because both contribution components flow from W-2 wages, there is a temptation to inflate salary to feed the plan. The IRS pushes back through its “reasonable compensation” standard: your salary needs to reflect what the market would pay for the work you actually do, weighing training and experience, time devoted to the business, comparable pay for similar roles, and the company’s dividend history.¹⁰

The tension runs in both directions. Owners who set salaries artificially low to minimize payroll taxes get audited for it, and owners who inflate salaries to maximize 401(k) room can raise separate questions. A $190,000 salary on $300,000 of total S corp income is defensible for most skilled professional roles. A $190,000 salary on $200,000 of total income is a harder sell.

Setup and Deadlines

You must adopt a written plan document by December 31 of the year you want to start making employee deferrals. Miss that date and you lose the entire year on the deferral side. Most brokerages, banks, and third-party administrators offer pre-approved plan documents. The plan also needs its own EIN, separate from the S corp’s EIN, for trust reporting purposes.⁴

Because S corp owners are W-2 employees, elective deferrals must be withheld from compensation paid during the tax year. In practice, that means the money comes out of paychecks processed by December 31, and you need a written deferral election in place before the compensation is paid.

The employer profit-sharing contribution is more flexible. The S corp can make it any time up to the tax filing deadline, including extensions. For a calendar-year S corp, Form 1120-S is due March 15, and a six-month extension pushes that to September 15.¹¹ That gap gives you room to fund the employer side when cash flow is uneven.

Form 5500-EZ Once Assets Grow

Once plan assets exceed $250,000 at the end of any plan year, you must file Form 5500-EZ.¹² If you maintain more than one one-participant plan, their combined assets count toward the $250,000 threshold. The deadline is the last day of the seventh month after the plan year ends — July 31 for calendar-year plans.

This is the compliance step people most often ignore, and the penalty is steep: $250 per day, up to $150,000 per plan year.¹³ A penalty relief program exists for late filers, but it is not something to plan around. You must also file a final 5500-EZ if you terminate the plan, even if assets are below $250,000.¹²

Prohibited Transactions

A Solo 401(k) is a trust, and the IRS heavily regulates transactions between you and the trust. You cannot sell property to the plan, borrow from it outside the formal loan rules, or use plan assets for personal benefit. These prohibited transactions carry a 15% excise tax on the amount involved for each year the transaction remains uncorrected, and a 100% tax if you fail to fix it.¹⁴ Common traps include paying personal expenses with plan funds, buying property you personally use, or lending plan money to your S corp. The IRS does not distinguish between innocent mistakes and deliberate abuse when assessing the tax.¹⁵

On the permitted side, if your plan document allows it, you can borrow up to the lesser of $50,000 or 50% of your vested balance (with a floor of $10,000), repaid with interest in substantially equal payments at least quarterly, over no more than five years unless the loan is for a primary residence.¹⁶

How It Stacks Up Against a SEP or SIMPLE IRA

S corp owners generally choose among three retirement plans. The Solo 401(k) wins on total contribution capacity for higher earners, but the alternatives have their place.

A SEP IRA allows only employer contributions, capped at 25% of W-2 compensation. There is no employee deferral. For an owner with a $190,000 salary, the SEP maximum is $47,500, compared to $72,000 through a Solo 401(k). Administration is simpler — no plan document complexity, no Form 5500-EZ — which appeals to owners who do not need the higher ceiling. SECURE 2.0 added Roth contributions to SEPs, though not every custodian has implemented the feature.⁸

A SIMPLE IRA has a much lower deferral limit: $17,000 for 2026, with certain small employers in business at least two years able to offer $18,100.¹⁷⁷ The employer match is capped at 3% of compensation, or a 2% nonelective contribution for all eligible employees. SIMPLE IRAs also impose a two-year waiting period before rolling funds to another retirement plan; rolling out earlier raises the early distribution penalty from 10% to 25%.¹⁸

For an S corp owner earning enough to want to save aggressively, the Solo 401(k) is the clearest fit. The SEP works when you want minimal paperwork and your target is under 25% of salary. The SIMPLE IRA is designed for small businesses offering employees a straightforward match and rarely fits a high-earning owner-only S corp.

1
Internal Revenue Service. COLA Increases for Dollar Limitations on Benefits and Contributions
2
Internal Revenue Service. S Corporation Employees, Shareholders and Corporate Officers
3
Internal Revenue Service. Retirement Plan FAQs Regarding Contributions – Are Retirement Plan Contributions Subject to Withholding for FICA, Medicare or Federal Income Tax
4
Internal Revenue Service. One Participant 401k Plans
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Fidelity Investments. Self-Employed 401(k) Overview
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Internal Revenue Service. Terminating a Retirement Plan
7
Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026
8
Internal Revenue Service. SECURE 2.0 Act Changes Affect How Businesses Complete Forms W-2
9
Internal Revenue Service. Consequences to a Participant Who Makes Excess Annual Salary Deferrals
10
Internal Revenue Service. Wage Compensation for S Corporation Officers
11
Internal Revenue Service. Publication 509 (2026), Tax Calendars
12
Internal Revenue Service. Instructions for Form 5500-EZ
13
Internal Revenue Service. Penalty Relief Program for Form 5500-EZ Late Filers
14
Internal Revenue Service. Retirement Topics – Tax on Prohibited Transactions
15
Internal Revenue Service. Retirement Topics – Prohibited Transactions
16
Internal Revenue Service. Retirement Plans FAQs Regarding Loans
17
Internal Revenue Service. Retirement Topics – SIMPLE IRA Contribution Limits
18
U.S. Department of Labor. SIMPLE IRA Plans for Small Businesses