Setting up a 401(k) for your small business involves four core steps: adopting a written plan document, establishing a trust for plan assets, building a recordkeeping system, and notifying eligible employees. The process typically takes a few weeks once you’ve chosen a provider, and tax credits introduced under the SECURE 2.0 Act can offset most or all of your startup costs for the first few years.
Choose the Right Plan Type
Not every 401(k) works the same way, and the version you pick affects your costs, paperwork, and how much flexibility you and your employees have. Here are the main options for small businesses.
Traditional 401(k)
A traditional 401(k) is open to any employer with one or more employees. It gives you the most design flexibility: you choose the matching formula, vesting schedule, and eligibility rules. The tradeoff is complexity. Each year you must run nondiscrimination tests (called ADP and ACP tests) to make sure highly compensated employees aren’t benefiting disproportionately compared to everyone else. If the plan fails those tests, you may need to refund contributions or face a 10% excise tax. You also file an annual Form 5500 with the Department of Labor.
Safe Harbor 401(k)
A safe harbor 401(k) eliminates annual nondiscrimination testing in exchange for a required employer contribution. You can satisfy the safe harbor by matching employee contributions (typically dollar for dollar on the first 3% of pay, then 50 cents on the dollar for the next 2%) or by making a flat 3% nonelective contribution to every eligible employee regardless of whether they contribute. All safe harbor employer contributions are immediately 100% vested, meaning employees own them right away. You still file Form 5500 each year, but you skip the headache and cost of discrimination testing.
Solo 401(k)
If you have no employees other than yourself (and possibly your spouse), a solo 401(k) is the simplest path. You can make contributions both as the employee (salary deferrals) and as the employer (profit sharing), which lets you shelter a significant amount of income. If your plan’s total assets stay at $250,000 or less, you don’t even need to file Form 5500.
SIMPLE IRA (an Alternative Worth Knowing About)
A SIMPLE IRA isn’t technically a 401(k), but it’s a common alternative for businesses with 100 or fewer employees. You can set it up using IRS model forms (5304-SIMPLE or 5305-SIMPLE), there’s no annual filing requirement for the employer, and the financial institution handles most of the paperwork. The downside: contribution limits are lower than a 401(k), and you can’t maintain another retirement plan alongside it.
Select a Plan Provider
Your provider handles the day-to-day mechanics: recordkeeping, compliance testing, investment options, and employee enrollment. You’ll encounter several layers of fees.
- Setup fees: Typically $500 to $3,000 depending on plan complexity.
- Recordkeeping: Around $45 or more per participant per year. Some providers bundle this into a flat monthly rate. As an example, one major provider charges $100 per month for up to four employees with no per-participant fee, then $100 per month plus $5 per participant for five or more.
- Investment management fees: Mutual fund expense ratios range from 0.05% to 2% of assets. Index funds sit at the low end. Actively managed funds cost more.
- Advisory fees: If you add an investment adviser to help select and monitor fund options, expect 0.10% to 0.50% of plan assets annually.
- Compliance testing: $500 to $1,500 per year for plans that require nondiscrimination testing (not needed for safe harbor plans).
- Audit costs: Plans with 100 or more eligible participants must undergo an independent audit, which can run $10,000 or more. Most small businesses fall below this threshold.
When comparing providers, ask for a fee disclosure that breaks out every charge. Some providers advertise low monthly rates but use higher-cost investment funds, which shifts the expense to your employees. Look at the total cost, including fund expense ratios, not just the sticker price.
Adopt a Written Plan Document
Every 401(k) legally starts with a written plan document. This document spells out the rules: who’s eligible, what the employer match is, when employees vest in employer contributions, how distributions work, and how the plan will be administered. Your provider will typically draft this for you. If you’re working without a provider, you can use a pre-approved plan document from the IRS, but most small businesses find it easier to let their provider or a retirement plan professional handle it.
You’re legally bound by the terms in this document, so read it carefully. If you want to change something later (say, adjusting your match formula), you’ll need a formal plan amendment.
Set Up a Plan Trust
Federal law requires that 401(k) assets be held in a trust, separate from your business accounts. The trust exists to protect employees: it ensures plan assets are used solely for participants and their beneficiaries. You’ll need to designate at least one trustee to oversee contributions, investments, and distributions. In many cases, the business owner serves as trustee, with the plan provider handling custodial duties.
This is one of the most important decisions you’ll make. The trustee has a fiduciary duty, a legal obligation to act in participants’ best interests. That means selecting reasonable investment options, keeping fees in check, and making sure contributions are deposited on time. If you set up your plan through insurance contracts, those contracts don’t need to be held in a separate trust.
Build a Recordkeeping System
You need a system to track contributions, investment earnings, loans, distributions, and participant account balances. Nearly every modern provider includes recordkeeping as part of their service, with online dashboards for both you and your employees. If you’re running a solo 401(k) through a brokerage, the brokerage typically handles recordkeeping for you.
The key operational requirement here is timely deposit of employee contributions. When you withhold money from an employee’s paycheck, you must deposit it into the plan trust as soon as it can reasonably be separated from your general business assets. For small plans, the Department of Labor provides a safe harbor of seven business days after withholding.
Notify Eligible Employees
Before the plan starts, you must tell eligible employees about their benefits, rights, and plan features. You’re required to provide a summary plan description (SPD), a plain-language document explaining how the plan works, what the contribution rules are, how to enroll, when they vest, and how to request distributions. Your provider will usually generate the SPD alongside the plan document.
For safe harbor plans, you must also send an annual safe harbor notice at least 30 days before the start of each plan year, explaining the employer contribution formula and employees’ rights.
Eligibility rules vary by plan design. Generally, you must offer the plan to all employees who are at least 21 years old and have worked at least 1,000 hours in a previous year. You can set a shorter waiting period or open enrollment more broadly, but you can’t make it more restrictive than that.
Claim Your Tax Credits
The SECURE 2.0 Act created generous tax credits for small businesses starting a retirement plan. You can claim these credits if you had 100 or fewer employees earning at least $5,000 in the preceding year, at least one participant is a non-highly compensated employee, and your employees weren’t covered by another plan you sponsored in the prior three tax years.
The startup cost credit covers expenses like provider setup fees, administration, and employee education. If you have 50 or fewer employees, the credit equals 100% of eligible costs, up to the greater of $500 or $250 per eligible non-highly compensated employee (maxing out at $5,000). Businesses with 51 to 100 employees get 50% of eligible costs, with the same cap structure. You can claim this credit for each of the plan’s first three years.
There’s also a separate credit for employer contributions. For businesses with 1 to 50 employees, the credit covers 100% of employer contributions in the first two plan years (up to $1,000 per participating employee), then steps down: 75% in year three, 50% in year four, and 25% in year five. For businesses with 51 to 100 employees, the credit phases down by 2% for each employee above 50. The contribution credit doesn’t apply to employees earning more than $100,000.
Between these two credits, many small businesses can launch a 401(k) with little or no net cost in the early years.
Stay Compliant Year After Year
Setting up the plan is the first step. Keeping it running properly is an ongoing responsibility.
Most 401(k) plans must file Form 5500 annually by the last day of the seventh month after the plan year ends (July 31 for calendar-year plans, with a possible extension). Small plans with fewer than 100 participants can typically use the simplified Form 5500-SF. Solo 401(k) plans covering only the owner and spouse can use Form 5500-EZ, and they’re exempt from filing entirely if total plan assets are $250,000 or less. All 5500 and 5500-SF filings must be submitted electronically through the Department of Labor’s EFAST2 system.
If you run a traditional 401(k) rather than a safe harbor plan, you’ll need to pass nondiscrimination testing each year. Your provider or third-party administrator typically handles this, but you should understand what it means: the tests compare contribution rates of highly compensated employees to those of rank-and-file workers. If the gap is too large, you’ll need to correct it by refunding excess contributions or making additional employer contributions. Failing to correct a testing failure by the end of the following plan year can disqualify the entire plan.
Safe harbor plans avoid this testing entirely, which is a major reason they’re popular with small businesses where owners want to maximize their own deferrals without worrying about whether enough employees are participating.