The Prudent Investor Rule: What Ontario Estate Trustees Must Know About Investing Estate Assets

Sitting on estate funds isn't a passive job. Whether an estate trustee is holding cash for a few months while an estate is settled, or managing a testamentary trust for years, Ontario's prudent investor rule sets a real legal standard for how that money must be handled. Leaving a large sum earning nothing in a low-interest account can be just as much a problem as putting it into something reckless.

Understanding what "prudent" actually means — and what it does not — helps trustees avoid a mistake that is easy to make with the best of intentions.

What the Prudent Investor Standard Means

Ontario's Trustee Act sets out an investment standard requiring a trustee to exercise the care, skill, diligence, and judgment that a prudent investor would apply when managing their own property. This is a standard of conduct, not a guarantee of results — a trustee who invests carefully and reasonably is not automatically at fault simply because an investment later performs poorly.

What Factors a Prudent Trustee Considers

• The overall portfolio, not each asset in isolation. A prudent investor evaluates how investments work together, not whether any single holding was, in hindsight, the best possible choice.
• Diversification. Concentrating estate funds in one asset or one type of investment generally increases risk without a corresponding benefit.
• The estate's actual needs. A short estate administration holding funds temporarily has very different needs than a testamentary trust meant to provide income for years.
• Time horizon. Money needed for near-term distribution should generally be managed more conservatively than funds held in a long-running trust.
• Beneficiaries' circumstances. A trust for a minor beneficiary, or one intended to support someone for decades, calls for a different approach than a short-term holding period.
• Costs of investing. Fees and transaction costs are a legitimate part of a prudent decision, not an afterthought.

Common Missteps That Can Breach the Standard

• Leaving a substantial sum sitting in a non-interest-bearing account for an extended period without good reason
• Putting estate funds into a single speculative or high-risk investment
• Failing to diversify across different types of assets where the estate's size and timeline would reasonably call for it
• Making investment choices based on the trustee's own financial goals or preferences rather than the estate's or trust's needs
• Ignoring professional advice without a sound reason for doing so

Getting Professional Investment Advice

Trustees are generally permitted to rely on qualified professional investment advice, and doing so can help demonstrate that the required standard of care was met. This does not mean a trustee can blindly hand off all responsibility — they still need to exercise reasonable oversight and judgment — but seeking and following sound professional advice is consistent with, not a substitute for, prudent conduct.

Revisiting the Strategy Over Time

Prudent investing is not a single decision made at the outset and then left alone. An estate's or trust's circumstances change — a trust that seemed likely to be short-term can end up running much longer than expected, or a beneficiary's needs can shift over time. Periodically revisiting the investment strategy, rather than treating the first decision as permanent, is itself part of what a prudent investor in the trustee's position would do.

Short-Term Estate Administration vs. Long-Term Trusts

The standard applies differently depending on context. A straightforward estate being wound up over a matter of months, mostly holding cash while assets are gathered and debts paid, has less need for an elaborate investment strategy than a testamentary trust — for example, a spousal trust or a trust for a minor or disabled beneficiary — that may operate for years. The longer the money will be held, the more the prudent investor standard expects a deliberate, ongoing investment strategy rather than a one-time decision.

Frequently asked questions