401(k) Plan Sponsor Responsibilities & Fiduciary Duties
Sponsoring a 401(k) makes the employer responsible for the plan — and ERISA spells out exactly what that means. Here are the duties every plan sponsor carries, what each one requires in practice, and how each leaves a public paper trail in the plan's Form 5500.
Last updated June 10, 2026
The four ERISA fiduciary duties
Everything a sponsor does for the plan is measured against four duties in ERISA §404(a):
- Loyalty — act solely in the interest of participants and beneficiaries, for the exclusive purpose of providing benefits and defraying reasonable expenses.
- Prudence — act with the care and skill of a knowledgeable expert. Prudence is judged on process: document how decisions get made.
- Diversification — offer a menu that lets participants diversify and minimize the risk of large losses.
- Follow the plan document — administer the plan exactly as written, as long as it's consistent with ERISA.
The responsibilities, one by one
- File Form 5500 every year. Due the last day of the 7th month after plan year-end — July 31 for calendar-year plans, October 15 with an extension. Late filings risk DOL penalties of up to $2,739 per day; the due-date guide covers deadlines and the DFVCP fix.
- Select and monitor providers. Hiring the recordkeeper, advisor, and TPA is a fiduciary act — and so is keeping them. Review performance and fees on a regular cycle and document it.
- Benchmark fees. Providers must disclose their compensation under ERISA §408(b)(2); the sponsor must conclude the fees are reasonable. Comparing what similar plans pay (public on Schedule C) is the standard way to do that.
- Deposit employee contributions on time. Deferrals must reach the trust as soon as they can reasonably be segregated from company assets. Small plans (under 100 participants) have a 7-business-day safe harbor. Late deposits are a top DOL audit finding.
- Distribute participant disclosures. The SPD, the annual §404(a)(5) fee disclosure, and any safe-harbor, QDIA, or auto-enrollment notices, all on schedule.
- Maintain an ERISA fidelity bond. At least 10% of funds handled, between $1,000 and $500,000 ($1M if the plan holds employer stock). The bond amount is reported on the Form 5500.
- Get an audit when the plan is large. Plans with roughly 100+ participants with balances attach an independent auditor's report — see the 401(k) audit requirements.
Every responsibility leaves a paper trail in the Form 5500
The annual filing is where a sponsor's diligence becomes public record. The filing date shows whether the deadline was met. Schedule C shows what the plan pays each provider. The audit report and the auditor's name are attached. The fidelity bond amount, late-deposit corrections, and participant counts are all line items. Reading a plan's filing history is the fastest way to see how well a sponsor runs its plan — yours or anyone else's.
Filing dates, provider fees, auditor, bond amounts, and participant counts — free, from the public Form 5500 data.
Look up a plan's filingsWhat sponsors can delegate — and what they can't
Sponsors can hire out most of the work: a 3(16) fiduciary to take on plan administration, a 3(21) advisor to recommend investments, a 3(38) investment manager to choose them with full discretion. What never transfers is the duty to prudently select and monitor whoever was hired. Delegation narrows the sponsor's job to oversight; it doesn't end it. The sponsor vs. administrator guide maps who holds which role.
Real plans whose Form 5500 arrived after the extended deadline — a late filing is the most visible sponsor lapse in the public record.
Search Form 5500 filingsFrequently asked questions
Acting as an ERISA fiduciary (loyalty, prudence, diversification, following the plan document), filing Form 5500 annually, selecting and monitoring providers, keeping fees reasonable, depositing employee contributions promptly, distributing required disclosures, maintaining a fidelity bond, and obtaining an audit once the plan is large.
Yes, whenever it exercises discretion over the plan — selecting investments, hiring providers, administering the plan. Plan-design decisions like setting the match are business decisions, but implementing and running the plan is fiduciary activity.
As soon as the money can reasonably be segregated from company assets. Plans with fewer than 100 participants have a DOL safe harbor of 7 business days after the payroll date. Late deposits must be corrected and reported.
Most of the work, yes — 3(16) administrators, 3(21) advisors, and 3(38) managers all exist for that. The duty to prudently select and monitor those providers stays with the sponsor and can't be delegated away.
The DOL can assess up to $2,739 per day with no cap, and IRS penalties can apply on top. The DFVCP program lets sponsors who come forward voluntarily fix late filings at sharply reduced amounts — $10 per day, capped at $2,000 per plan per year.