Definition
The prudent investor rule is the general trust-law standard of care that requires a trustee to invest and manage trust assets the way a prudent investor would, judged against the overall portfolio and its purposes rather than against any single holding in isolation.
Why it matters
The prudent investor rule is the general standard that ERISA's prudent expert standard is built on. Distinguishing the two makes it possible to describe why ERISA fiduciary duty is more demanding than ordinary trustee duty, and why the presence of the ERISA overlay changes what a fiduciary is required to know and to do.
How it works
The prudent investor rule as codified by the Uniform Prudent Investor Act (adopted in most states) and its Restatement (Third) of Trusts predecessor replaced an earlier prudent-man rule that evaluated each investment on its own for prudence. Under the modern prudent investor rule, prudence is evaluated at the portfolio level rather than at the individual-holding level, with modern portfolio theory concepts — diversification, correlation, risk-adjusted return — recognized as legitimate elements of trustee analysis. A trustee is required to consider the trust's purposes, its distribution requirements, its beneficiaries' circumstances, and general economic conditions in constructing the portfolio. A holding that would be imprudent standing alone may be prudent as part of a diversified portfolio; conversely, a portfolio of individually conservative holdings can still be imprudent if it fails to serve the trust's purposes. The rule is a default that a trust document can modify but does not eliminate.
In practice
For an individual DC plan participant, the prudent investor rule sits behind the ERISA standard the plan's fiduciaries actually operate under, which is the more demanding prudent expert standard treated separately. The prudent investor rule is more directly operative in non-ERISA trust contexts — personal trusts, non-qualified deferred compensation, certain public plans, and other trust arrangements where ERISA does not apply. For plan fiduciaries, understanding the prudent investor rule matters because case law and academic commentary on ERISA fiduciary duty draw on trust-law precedent, and because state-law fiduciary standards for non-ERISA arrangements a participant may hold outside the plan are often based directly on the prudent investor rule. Individuals evaluating any trust-based lifetime income arrangement should ask whether the arrangement's fiduciary structure is governed by ERISA (the elevated standard) or by state trust law (the general standard).
Related terms
- Prudent expert standard
- ERISA Section 404
- ERISA fiduciary
- Trustee
- Uniform Prudent Investor Act
- Modern portfolio theory
- Diversification requirement
- Fiduciary breach