Who is a fiduciary to a 401(k) plan?
Last updated October 2, 2026
Anyone with discretionary authority over a 401(k) plan's management, administration, or assets is a fiduciary — the employer sponsoring the plan, the named plan administrator, investment committee members, and advisers with investment discretion. Function, not title, determines fiduciary status.
ERISA defines 401(k) fiduciaries functionally. You are a fiduciary to the extent you exercise discretion over plan management or assets, render investment advice for a fee, or have discretionary responsibility for administration.
The usual cast:
- The employer/plan sponsor and officers who make plan decisions
- The named plan administrator and any retirement or investment committee
- Trustees with authority over plan assets
- 3(21) advisers (co-fiduciary advice) and 3(38) investment managers (discretionary)
Recordkeepers and TPAs performing ministerial work generally are not fiduciaries — which means the discretion, and the responsibility, stays with the employer's people. Naming a committee and running it well is how that responsibility becomes manageable.
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