How to Set Up a Small Business 401(k) With Vanguard

To set up a small business 401(k) with Vanguard, you pick a plan structure that matches your workforce, settle a handful of design decisions, adopt Vanguard’s pre-approved plan document to create the trust, connect the plan to your payroll system, choose an investment menu, and enroll your eligible employees before the plan’s effective date. Vanguard’s employer-sponsored 401(k) is built for small to midsize businesses and gives participants access to Vanguard mutual funds, ETFs, and additional brokerage options, with Roth contributions available.¹ Two SECURE 2.0 tax credits can reimburse most of your startup and employer-contribution costs for the first several years, which means the net cost of running a well-designed plan is often close to zero at the outset.²

Pick the Plan Structure That Fits Your Business

The first decision drives everything that follows, and it hinges almost entirely on whether you employ anyone beyond yourself and a spouse.

Solo 401(k)

A solo 401(k) covers only a business owner with no employees, or the owner and their spouse. It is not a separate plan type under the tax code. It is a traditional 401(k) that qualifies for simplified administration because there are no rank-and-file employees to test against. That simplification disappears the moment you hire someone who meets the plan’s eligibility rules, at which point you either bring them in and begin nondiscrimination testing or convert to a safe harbor design.³

The appeal of the solo 401(k) is that you contribute from both sides of the table. As the employee, you can defer up to the annual elective limit. As the employer, you can add a profit-sharing contribution of up to 25% of your W-2 wages if the business is incorporated, or approximately 20% of net self-employment income if it is not. The lower percentage for self-employed owners reflects the deduction of half of self-employment tax before the percentage is applied.⁴

Traditional 401(k) With Employees

Once your plan covers non-owner employees, it has to pass annual nondiscrimination tests to keep its tax-qualified status. The two main ones are the Actual Deferral Percentage (ADP) and Actual Contribution Percentage (ACP) tests, which compare what highly compensated employees save against what everyone else saves.⁵ A separate top-heavy test checks whether key employees hold more than 60% of plan assets; if they do, the employer generally owes a minimum 3% contribution to every non-key employee.⁶

Testing happens after the plan year ends. If the plan fails, you correct it by returning excess contributions to highly compensated employees or by contributing more for everyone else. If there is any real chance your owners and managers will save at a much higher rate than the rank-and-file, a safe harbor design is almost always the better path.

Safe Harbor 401(k)

A safe harbor 401(k) is a traditional 401(k) with a design feature bolted on: in exchange for a mandatory, fully vested employer contribution, the plan automatically satisfies the ADP and ACP tests.⁷ You commit to a specific formula, and in return owners and highly compensated employees can defer up to the legal maximum without worrying about failed tests.

The three common safe harbor formulas:

Basic match: 100% of the first 3% of compensation deferred, plus 50% of the next 2%, capped at 4% of each participant’s pay.
Enhanced match: at least as generous as the basic match, applied to no more than 6% of compensation. A dollar-for-dollar match on the first 4% is common.
Nonelective contribution: 3% of compensation to every eligible employee, whether they defer anything or not.

Safe harbor contributions must be 100% vested immediately, with one carve-out: a Qualified Automatic Contribution Arrangement (QACA) safe harbor can use a two-year cliff vesting schedule for its matching contributions.⁸

Lock In the Plan Design

Settle these decisions before you start on paperwork. Changing them later usually requires a formal plan amendment.

Eligibility

Federal law sets the strictest rules you are allowed to impose: employees must be allowed in once they reach age 21 and complete one year of service, defined as a 12-month period with at least 1,000 hours worked.⁹ You can be more generous, with a shorter waiting period or no age minimum, but not more restrictive. SECURE 2.0 also opened the door for long-term part-time workers to make elective deferrals once they complete at least 500 hours in each of two consecutive 12-month periods, even if they never hit 1,000.

Vesting

Employee deferrals are always 100% vested immediately. Non-safe-harbor employer contributions can follow a cliff schedule, where employees become fully vested after a set number of years, or a graded schedule that phases in over time. Safe harbor contributions must be fully vested when made, with the QACA matching exception noted above.⁸

Employer Contribution Formula

Decide whether you will offer a match, a profit-sharing contribution, both, or neither. A discretionary profit-sharing contribution gives you year-by-year flexibility to choose whether and how much to contribute. A safe harbor match or nonelective contribution locks you in for the plan year but eliminates testing. Small businesses whose owners want to maximize their own deferrals almost always go safe harbor.

Automatic Enrollment

Most new 401(k) plans established after December 29, 2022, must include automatic enrollment starting in plan years beginning after December 31, 2024. The default deferral rate must sit between 3% and 10% in the first year, and must escalate by 1% annually until reaching at least 10%, with a ceiling of 15%. Employees can always opt out or change their rate.

Exemptions apply to businesses that normally employ 10 or fewer people, businesses less than three years old, church plans, governmental plans, and SIMPLE 401(k) plans. Plans adopted on or before December 29, 2022, are grandfathered.

Know the 2026 Contribution Limits

Every dollar figure in a 401(k) adjusts annually for inflation. For 2026 the key numbers are:⁴

Employee elective deferral: $24,500.
Catch-up contribution for ages 50–59 or 64 and older: an additional $8,000, bringing the total to $32,500.
Enhanced catch-up for ages 60–63: an additional $11,250 instead of $8,000, for a total deferral of $35,750. SECURE 2.0 created this higher limit for that narrow age window.
Total annual addition from employee and employer combined: $72,000, not counting catch-up contributions.
Compensation cap: $360,000. Only this much of any employee’s pay counts when calculating employer contributions.

A solo 401(k) owner under 50 earning at least $360,000 can reach the full $72,000 by combining a $24,500 deferral with enough employer profit-sharing to fill the cap. Owners aged 60–63 can push that figure to $83,250 with the enhanced catch-up.¹

Claim the SECURE 2.0 Tax Credits

Two credits can offset most of what you spend to start and fund a new plan. Both are claimed on IRS Form 8881.²

Startup Costs Credit

Employers with 50 or fewer employees who received at least $5,000 in compensation can claim a credit equal to 100% of qualified startup costs for the first three years of the plan. Qualified costs include plan administration expenses and retirement-related employee education. The annual credit is capped at the greater of $500 or the lesser of $250 multiplied by the number of eligible non-highly compensated employees, or $5,000.¹⁰ Employers with 51 to 100 employees take the credit at 50% rather than 100%. You cannot claim it if you maintained a qualified plan covering substantially the same employees during the prior three tax years.

Employer Contributions Credit

A separate credit covers actual employer contributions, not employee deferrals, up to $1,000 per employee who earned $105,000 or less. The credit phases down over five years: 100% in years one and two, 75% in year three, 50% in year four, and 25% in year five.² For employers with more than 50 employees, the percentage is reduced by 2% for each employee above 50.

The Setup Steps With Vanguard

With your structure and design locked in, the mechanical process has a clear sequence.

Gather Business and Employee Data

You will need the company’s legal name, Employer Identification Number, desired plan effective date, and plan year-end date. Most small businesses use a calendar year. You also need census data for every employee: names, birth dates, hire dates, annual compensation, and hours worked. That data determines who is eligible and feeds your initial compliance projections.

Adopt the Plan Document and Establish the Trust

The plan document is the legal foundation. It sets out every rule: eligibility, contributions, vesting, distributions, and loans. Vanguard provides a pre-approved plan document as part of its setup process. Adoption of the document creates a trust that holds all contributions and plan assets separately from your company’s operating accounts. Every dollar must flow through the trust and stay legally distinct from business funds.

Timing matters here. A traditional 401(k) can be adopted as late as the due date of your tax return, including extensions, and still be effective for the prior tax year, though employee deferrals cannot be made retroactively. A safe harbor plan must be adopted at least three months before the plan year ends, which means October 1 for a calendar-year plan.¹¹

Integrate With Payroll

Payroll integration is where plans either run cleanly or fall apart. Your payroll system has to deduct the correct deferral from each paycheck, apply catch-up limits for eligible employees, and transmit the funds to the plan trust. For plans with fewer than 100 participants, the Department of Labor treats employee deferrals as timely if they reach the trust within seven business days of being withheld.¹² Missing that window can be treated as a prohibited transaction, so build in margin. Most modern payroll providers have direct feeds to Vanguard’s recordkeeping platform.

Select Investments

Vanguard’s small business 401(k) offers access to Vanguard mutual funds and ETFs, plus additional brokerage options for participants who want wider selection.¹ As plan sponsor, you select the core menu. That is a fiduciary decision, so build a diversified lineup covering the major asset classes at reasonable cost. Target-date funds are a common default investment because they adjust asset allocation automatically as participants approach retirement.

Enroll Employees and Distribute the Summary Plan Description

Before the effective date, hold an enrollment meeting and give every eligible employee the Summary Plan Description (SPD). The SPD explains the plan’s rules in plain language: how to enroll, contribution limits, the investment menu, vesting schedules, and distribution rules. If you are using automatic enrollment, the notice must clearly state the default deferral rate, the annual escalation schedule, and how to opt out.

What You’re On the Hook For Each Year

Opening the plan is the easy part. Running it correctly is where the real work sits.

Fiduciary Duty

As plan sponsor, you are a fiduciary under the Employee Retirement Income Security Act (ERISA). You must act solely in participants’ interests, select and monitor investments prudently, keep fees reasonable, and follow the plan document.¹³ ERISA also requires fiduciaries to diversify investments to minimize the risk of large losses and to avoid conflicts of interest.¹⁴

ERISA Fidelity Bond

Plans covering more than one participant must carry an ERISA fidelity bond equal to at least 10% of plan assets, with a minimum of $1,000 and a maximum of $500,000.¹⁵ The bond is separate from fiduciary liability insurance; it protects the plan against losses caused by fraud or dishonesty by anyone who handles plan funds.

Form 5500

Most 401(k) plans file an annual return with the IRS and Department of Labor using the Form 5500 series. The deadline is the last day of the seventh month after your plan year ends, which is July 31 for calendar-year plans. A one-time extension is available by filing Form 5558.¹⁶ All 5500-series forms must be filed electronically.¹⁷

Solo 401(k) plans get a break. You do not need to file Form 5500-EZ unless total assets across all your one-participant plans exceed $250,000 at the end of the plan year.¹⁸ That threshold applies to your combined one-participant plans, not each one individually.

Nondiscrimination and Top-Heavy Testing

Traditional 401(k) plans without a safe harbor design must pass ADP and ACP testing every year.⁵ Safe harbor plans skip those two tests entirely, which is their main appeal.⁷ The top-heavy test, however, applies to every 401(k), safe harbor included. If key employees own more than 60% of plan assets as of the last day of the prior plan year, the plan is top-heavy and the employer generally must contribute at least 3% of compensation for every non-key employee still employed at year-end.⁶ In practice, a safe harbor nonelective contribution of 3% typically satisfies that requirement too, so safe harbor plans rarely trigger extra top-heavy costs.¹⁹

Ongoing Administration

You also need to review the investment lineup periodically, benchmark plan fees, process participant loans and hardship withdrawals according to the plan document, and amend the plan for new legislation. Most small businesses hire a third-party administrator to run testing, filings, and compliance monitoring. That typically runs between $500 and $1,500 per year for a small plan, though it varies by provider and complexity. Between the SECURE 2.0 credits and the deductibility of plan administration expenses, the net cost of a well-managed plan is often close to zero in the early years.

1
Vanguard. Compare Small-Business Retirement Plans
2
Internal Revenue Service. Instructions for Form 8881
3
Internal Revenue Service. One-Participant 401(k) Plans
4
Internal Revenue Service. COLA Increases for Dollar Limitations on Benefits and Contributions
5
Internal Revenue Service. 401(k) Plan Fix-It Guide – The Plan Failed the 401(k) ADP and ACP Nondiscrimination Tests
6
Internal Revenue Service. Is My 401(k) Top-Heavy?
7
Internal Revenue Service. Chapter 7 – 401(k) Determination Issues
8
Internal Revenue Service. Issue Snapshot – Vesting Schedules for Matching Contributions
9
Internal Revenue Service. 401(k) Plan Qualification Requirements
10
Office of the Law Revision Counsel. 26 US Code 45E – Small Employer Pension Plan Startup Costs
11
Internal Revenue Service. Issue Snapshot – Deductibility of Employer Contributions to a 401(k) Plan Made After the End of the Tax Year
12
U.S. Department of Labor. 401(k) Plans for Small Businesses
13
U.S. Department of Labor. Fiduciary Responsibilities
14
Office of the Law Revision Counsel. 29 US Code 1104 – Fiduciary Duties
15
Internal Revenue Service. Employee Plans LESE Project – Defined Contribution Plans With Less Than $250,000 in Assets
16
Internal Revenue Service. Form 5500 Corner
17
U.S. Department of Labor. Form 5500 Series
18
Internal Revenue Service. Financial Advisors Are Assets in Your Clients One-Participant Plans More Than $250,000
19
Internal Revenue Service. 401(k) Plan Fix-It Guide – The Plan Was Top-Heavy and Required Minimum Contributions Were Not Made to the Plan