401(k) plan documents: what each one is for
A 401(k) is governed by a small stack of documents, and they do genuinely different jobs. One is the law of the plan. One is the version employees are entitled to read. One is issued only when something changes. Confusing them is how plans end up operating differently from how they are written.
A 401(k) runs on a written plan document, a trust holding its assets, a summary plan description given to every participant, a summary annual report each year, and a summary of material modifications whenever the plan changes.
Employers usually meet these documents as a pile of paperwork at setup and never look at them again. That is a mistake with a specific consequence: when the plan is operated differently from how the plan document is written, the document wins, and the difference has to be corrected — sometimes years later, at the employer's expense.
The plan document is the law of the plan
The IRS requires that a plan be established under a definite written program that is communicated to employees. This document is the authority for every operational question that ever arises: who is eligible and when they enter, what compensation counts, what the match formula is, how vesting works, whether loans are permitted, what happens on termination.
When a question comes up, the answer is whatever the plan document says — not what the payroll system does, not what the last administrator did, and not what everyone assumed. If the document and the practice disagree, the practice is the error. This is the single most useful thing to understand about plan documents, and it is why reading yours once is worth the hour.
The document also has to stay current as the law changes. Legislation like SECURE 2.0 alters what plans must and may do, and those changes eventually have to be reflected in the document itself rather than only in operation.
The trust
401(k) plans are funded through a trust established to hold and invest the plan's assets, with at least one trustee. The IRS notes the trustee may be the business owner, an employee, or a financial or trust institution. The trust is what keeps plan assets legally separate from the employer's own money — which is the same principle behind the deferral deposit rules, and the reason withheld deferrals stop being company money the moment they are withheld.
What employees are entitled to receive
| Document | What it is | When it is provided |
|---|---|---|
| Summary plan description (SPD) | The plan explained in readable form: eligibility, how benefits are calculated, vesting, payment options, and claims procedures. | Automatically on becoming a participant or beneficiary. The plan administrator is legally obligated to provide it free of charge. |
| Summary of material modifications (SMM) | Notice of a change to the plan. May instead be issued as a revised SPD. | Automatically when the plan is modified. Also free of charge. |
| Summary annual report (SAR) | A summary of the plan's annual financial report — the Form 5500 filed with the Department of Labor. | Automatically each year, at no cost to participants. |
All three are the plan administrator's obligation. In a pooled employer plan that role sits with the pooled plan provider rather than with each participating employer.
The documents that depend on your design
Beyond the core set, some documents exist only because of a choice the plan made.
- Safe harbor notice — required where the plan uses a safe harbor design, and subject to its own timing: at least 30 days and not more than 90 days before the beginning of each plan year, including a new plan's first year.
- Automatic enrolment notice — required where the plan enrols employees by default, which most plans established after the SECURE 2.0 enactment date must now do.
- Investment policy statement — not required by statute, but it is the written standard against which the investment menu is selected and monitored, and it is what makes that monitoring reviewable rather than a matter of opinion.
- Fee disclosures — participants are entitled to be told what the plan and its investments cost them. Where a plan charges a flat participant fee, this is where it is disclosed.
The annual return
Form 5500 is the plan's annual report to the Department of Labor and the IRS. It is due on the last day of the seventh month after the plan year ends, with an extension available on Form 5558. The summary annual report given to participants is a plain-language summary of it.
Whether a plan needs an independent auditor's report alongside the Form 5500 turns on a participant count, and the counting method changed for 2023 plan years — it is now based on participants with an account balance rather than everyone eligible. That change moved a substantial number of plans out of the audit requirement, and it is covered in the setup cost guide below.
In a pooled employer plan, the provider files one Form 5500 covering every participating employer. That is one of the few genuinely structural differences between a PEP and running your own plan — not a service level, but a different filing obligation.
What to actually do with all this
Two things, once. Read your own plan document's definitions of compensation, eligibility and entry dates, and check that payroll is actually doing what they say. And confirm who is responsible for issuing the SPD, the SAR and any modification notice — because that is the plan administrator's duty, and the answer differs depending on how your plan is structured.
Common questions
What documents do I need for a 401(k)?
A written plan document establishing the plan, a trust to hold its assets, a summary plan description for participants, a summary annual report each year, and a summary of material modifications whenever the plan changes. Depending on your design you may also need a safe harbor notice, an automatic enrolment notice, and fee disclosures.
What is a summary plan description?
The plan explained in readable form — eligibility, how benefits are calculated, vesting, payment options and claims procedures. The plan administrator is legally obligated to provide it to participants free of charge, automatically on becoming a participant or beneficiary.
What happens if the plan document and actual practice disagree?
The plan document governs, and the practice is the error. It has to be corrected, which is why checking that payroll matches the document's definitions of compensation, eligibility and entry dates is worth doing once rather than discovering the gap years later.
What is a summary annual report?
A summary of the plan's annual financial report — the Form 5500 filed with the Department of Labor. The plan administrator must automatically give participants a copy each year at no cost.
Who issues these documents in a pooled employer plan?
The pooled plan provider, because it holds the plan administrator role. It also files a single Form 5500 covering all participating employers, rather than each employer filing its own.
Sources
- Internal Revenue Service, 401(k) Resource Guide — Starting Up Your Plan — the definite written program requirement, the trust and who may serve as trustee, and the summary plan description
- U.S. Department of Labor, Retirement Plan Information for Participants — that the plan administrator is legally obligated to provide the SPD free of charge, that a modification requires a revised SPD or a summary of material modifications, and that the summary annual report is provided automatically each year
- Internal Revenue Service, 401(k) Plan Overview — the safe harbor notice window of at least 30 and not more than 90 days before the plan year
- U.S. Department of Labor, Form 5500 Series — the annual return, its deadline of the last day of the seventh month after the plan year ends, and the Form 5558 extension
- U.S. Department of Labor, Changes for the 2023 Form 5500 and Form 5500-SF Annual Return/Reports — the participants-with-account-balances counting method that determines whether an independent audit is required
aipep401k.com is a pooled employer plan for small business 401(k) plans, operated by ThinkNirvana Foundation — plan administration handled by automation rather than assembled by hand.
Related: what moves between payroll and the plan, what drives the cost of setting one up. To see what a plan design would look like for your own headcount, the plan design tool is free and needs no sign-up.