Any LLC can sponsor a 401(k) for its owners and employees, but the type of plan you use and the way contributions are calculated depend on two things: how your LLC is taxed federally, and whether anyone besides you and your spouse works for the business. For 2026, you can defer up to $24,500 of your own compensation, and combined employee-plus-employer contributions cap out at $72,000 before catch-up amounts.
Why Your LLC’s Tax Classification Matters First
Before you shop for a plan, know how the IRS treats your LLC. That single fact drives the math on every contribution you’ll make.
A single-member LLC defaults to “disregarded entity” status, so the IRS treats you as a sole proprietor reporting on Schedule C.1Internal Revenue Service. Single Member Limited Liability Companies A multi-member LLC defaults to partnership status and files Form 1065.2Internal Revenue Service. LLC Filing as a Corporation or Partnership In either case the owners are self-employed, and plan compensation is net self-employment income rather than a salary.
Either LLC type can instead elect corporate taxation by filing Form 8832 or Form 2553 (S-corporation). That election makes you a W-2 employee of your own company, and your plan contributions get calculated from W-2 wages. All four classifications — disregarded entity, partnership, S-corp, C-corp — can sponsor a 401(k). The classification doesn’t decide eligibility. It decides the math.
Solo 401(k) for an Owner-Only LLC
If the only people working in the LLC are you and possibly your spouse, a solo 401(k), also called a one-participant plan, is the simplest route. You act as both employer and employee, contributing from both sides, and you can usually shelter far more income than an IRA would allow.
Setup Steps
Confirm your LLC has an Employer Identification Number. The plan operates as a trust and needs the EIN for any annual reporting.3Internal Revenue Service. Understanding Your EIN
Choose a provider. Brokerages and specialized retirement companies offer pre-approved solo 401(k) documents. Compare fees, investment options, and whether the provider supports Roth contributions and participant loans, since those features vary even though the IRS allows both.
Adopt the plan document before the deadline. The plan can’t take effect earlier than the first day of the tax year in which you adopt it, and the 401(k) deferral feature can’t be made effective before the actual adoption date. You can’t retroactively defer salary you already received. To make employee deferrals for 2026, get the plan document signed by December 31, 2026. Employer profit-sharing contributions have a more generous deadline and can be funded up to your tax filing deadline, including extensions.4Internal Revenue Service. 401(k) Resource Guide – Plan Sponsors – Starting Up Your Plan
When You Outgrow the Solo Plan
A solo 401(k) works only when no employees are eligible for the plan. Federal law lets a plan require one year of service (a 12-month period with at least 1,000 hours worked) and a minimum age of 21 before an employee becomes eligible.5Office of the Law Revision Counsel. 26 USC 410 – Minimum Participation Standards Those are the maximum restrictions you can impose. Hire someone who clears both hurdles, and you’ll need to transition to a plan that covers employees.
Setting Up a 401(k) When Your LLC Has Employees
Once staff beyond you and your spouse enter the picture, you need a plan that covers eligible workers, and you’re now in ERISA territory. That adds real administrative weight.
Engage a third-party administrator. A TPA handles plan design, drafts the formal plan document, manages compliance testing, and prepares government filings. One-time setup fees typically run $500 to $3,000, with ongoing annual costs on top. Pricing varies widely, so shop around.
The plan document is the legal backbone of the 401(k). It specifies eligibility rules, vesting schedules for employer contributions, the contribution types allowed (pre-tax deferrals, Roth deferrals, employer match, profit-sharing), and how the plan runs day to day. Your TPA drafts it around the decisions you make on plan design.
Payroll has to be compliant too. Employee deferrals must be withheld from paychecks and deposited into the plan trust promptly. The Department of Labor requires deferrals to be segregated from the business’s general assets on the earliest date you can reasonably do so, and no later than the 15th business day of the following month.4Internal Revenue Service. 401(k) Resource Guide – Plan Sponsors – Starting Up Your Plan Before the plan’s effective date, each eligible employee must receive a Summary Plan Description explaining the terms.
Auto-Enrollment Rules for New Plans
Under IRC Section 414A, for plan years beginning after December 31, 2024, new 401(k) plans must automatically enroll eligible employees at a default rate between 3% and 10% of compensation. That rate must increase by one percentage point each year until it reaches at least 10%, with a cap of 15%. Employees can opt out or set their own rate at any time.6Office of the Law Revision Counsel. 26 USC 414A – Requirements Related to Automatic Enrollment
Three exemptions matter for small LLCs:
- Employers that normally employ 10 or fewer people are exempt.
- Businesses that have existed fewer than three years are exempt.
- SIMPLE 401(k) plans are excluded from the mandate entirely.
A brand-new LLC setting up its first plan can often qualify under both the small-employer and new-business exemptions, but the requirement kicks in as the business grows past those thresholds. Solo 401(k) plans aren’t affected, since there are no employees to enroll.6Office of the Law Revision Counsel. 26 USC 414A – Requirements Related to Automatic Enrollment
Traditional vs. Safe Harbor
An LLC with employees also chooses between a traditional and a safe harbor plan design. The difference is testing versus guaranteed contributions.
A traditional plan is subject to annual ADP and ACP nondiscrimination tests, which compare how much highly compensated employees defer and receive in matching contributions relative to everyone else.7Internal Revenue Service. 401(k) Plan Fix-It Guide – The Plan Failed the 401(k) ADP and ACP Nondiscrimination Tests Fail the tests and you either return excess contributions to highly compensated employees or make additional contributions for everyone else. Testing adds cost and unpredictability, and it limits how much owners can defer when rank-and-file employees don’t contribute much.
A safe harbor plan skips nondiscrimination testing in exchange for a mandatory employer contribution. You commit upfront to one of three formulas:
- Basic match: 100% of employee deferrals up to 3% of pay, plus 50% of deferrals between 3% and 5% of pay.
- Enhanced match: 100% of deferrals up to 4% of pay.
- Nonelective contribution: 3% of pay to all eligible employees, whether or not they defer anything.
Safe harbor employer contributions must be immediately 100% vested; you can’t impose a vesting schedule on them. You also have to send employees an annual notice at least 30 days and no more than 90 days before each plan year begins.8Internal Revenue Service. Notice Requirement for a Safe Harbor 401(k) or 401(m) Plan For employees who become eligible mid-year, the notice must reach them no later than their eligibility date. For many small LLCs the guaranteed cost is worth it, because it removes the risk of failed testing and lets owners maximize their own deferrals.
2026 Contribution Limits
All 401(k) plans share the same IRS dollar limits, but the employer piece is calculated differently depending on tax classification.
Employee Deferrals
You can defer up to $24,500 of compensation into your 401(k) in 2026. If you’re 50 or older, an $8,000 catch-up brings the deferral ceiling to $32,500.9Internal Revenue Service. IRS Notice 2025-67 – 2026 Amounts Relating to Retirement Plans and IRAs If you turn 60, 61, 62, or 63 during 2026, the catch-up jumps to $11,250, putting the ceiling at $35,750.10Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 The enhanced catch-up for that four-year window came from SECURE 2.0 and is worth planning around if you’re in it.
The $24,500 cap covers combined pre-tax and Roth deferrals. If your plan allows Roth, you can split the total however you like, but the combined amount can’t exceed the limit.
Employer Profit-Sharing
An LLC taxed as an S-corp or C-corp calculates the employer contribution from your W-2 salary. The LLC can contribute up to 25% of W-2 wages as profit-sharing.11Internal Revenue Service. One-Participant 401(k) Plans On a $150,000 salary, that’s up to $37,500 from the employer side.
An LLC taxed as a sole proprietorship or partnership uses net self-employment income instead: business profit minus the deductible half of self-employment tax. Because the contribution itself reduces the income it’s calculated against, the effective cap works out to roughly 20% of adjusted net earnings rather than 25%.12Internal Revenue Service. Self-Employed Individuals – Calculating Your Own Retirement Plan Contribution and Deduction IRS Publication 560 has worksheets for the circular math.
Total Ceiling
Combined employee deferrals and employer contributions can’t exceed $72,000 for 2026, not counting catch-up amounts.9Internal Revenue Service. IRS Notice 2025-67 – 2026 Amounts Relating to Retirement Plans and IRAs With the standard age-50 catch-up the ceiling is $80,000. With the enhanced catch-up for ages 60–63, it reaches $83,250.
Tax Credits That Offset Startup Costs
Small LLCs get two federal credits that work together to reduce the cost of starting a plan.
The startup costs credit is available to employers with 100 or fewer employees who earned at least $5,000 in the prior year, as long as at least one participant is a non-highly compensated employee. For LLCs with 50 or fewer employees, the credit covers 100% of eligible startup costs, such as plan setup, TPA fees, and employee education. For 51 to 100 employees, it covers 50%. Either way, the maximum is $5,000 per year for three years.13Internal Revenue Service. 14Internal Revenue Service. Form 5500 Corner The version depends on plan size.
Solo 401(k) plans don’t file Form 5500-EZ until total assets across all your one-participant plans exceed $250,000 at year-end. Once you cross that threshold you file annually for each plan you maintain.15Internal Revenue Service. Assets in One-Participant Plans More Than $250,000 A terminating plan files a final return regardless of asset level.16Internal Revenue Service. Instructions for Form 5500-EZ
Plans with fewer than 100 participants can file the shorter Form 5500-SF if they meet certain conditions, including holding all assets in investments with a readily determinable fair value and holding no employer securities.17Department of Labor. Instructions for Form 5500-SF Short Form Annual Return/Report of Small Employee Benefit Plan Plans with 100 or more participants file the full Form 5500 and need an independent audit by a qualified public accountant.
Missing the filing deadline is expensive. The IRS can assess a penalty of $250 per day, up to $150,000, for each late return.18Internal Revenue Service. Penalty Relief Program for Form 5500-EZ Late Filers The DOL imposes its own separate daily penalty on top of that.
Nondiscrimination Testing
Traditional 401(k) plans with non-owner employees must pass ADP and ACP tests each year.7Internal Revenue Service. 401(k) Plan Fix-It Guide – The Plan Failed the 401(k) ADP and ACP Nondiscrimination Tests If the plan fails, you correct the imbalance, usually by refunding excess contributions to highly compensated employees or by making additional contributions for rank-and-file workers. Your TPA handles the testing, but corrective costs come out of the business. Safe harbor plans that meet their contribution and notice requirements are exempt from ADP and ACP testing entirely.
Fiduciary Basics
Sponsoring a 401(k) makes you a fiduciary under ERISA if you manage plan investments, control plan assets, or make administrative decisions about the plan. You must run the plan solely in participants’ interests, invest prudently with appropriate diversification, follow the plan document, and avoid conflicts of interest. Breaching these duties can make you personally liable for plan losses, and courts can remove a fiduciary who violates them.19U.S. Department of Labor. Fiduciary Responsibilities
Plans with more than one participant generally need an ERISA fidelity bond covering at least 10% of plan assets, with a minimum of $1,000 and a maximum of $500,000, to protect participants against fraud or dishonesty by anyone handling plan funds.20Internal Revenue Service. Defined Contribution Plans With Less Than $250,000 in Assets For a solo 401(k), fiduciary duties technically apply, but the practical stakes are lower since you’re the only beneficiary.