Fluctuating Capacity in Ontario: How the Law Treats Good Days and Bad Days

Capacity is rarely a light switch. Many people, especially those living with early-stage dementia, recovering from delirium, or managing a condition with good days and bad days, are fully capable of making decisions some days and struggle on others. Ontario law has to grapple with this reality, and understanding fluctuating capacity under Ontario law matters for families trying to figure out what a loved one can still decide for themselves.

This is a genuinely nuanced area, and the right answer often depends heavily on the specific decision and the specific day. The general principles below are a starting point, not a substitute for a proper capacity assessment.

Capacity Is Decision-Specific, Not All-or-Nothing

One of the most important things to understand is that Ontario law does not treat capacity as a single global switch that's either on or off for a person. Capacity is assessed for a particular decision, at a particular time. A person might lack the capacity to manage complex investments while still clearly understanding a simpler decision, like signing a straightforward gift or naming a substitute decision-maker.

This matters directly for fluctuating conditions. A person having a genuinely lucid, engaged day may be capable of executing a valid will or power of attorney on that day, even if their capacity would be questionable on a harder day later that same week.

Capacity Is a Legal Standard, Not a Medical Diagnosis

A diagnosis, whether dementia, delirium, or another cognitive condition, does not by itself mean a person lacks legal capacity. Testamentary capacity, for example, is a legal standard assessed at the time a will was actually made, not a medical label applied after the fact. The same logic extends to other decisions: the question is always whether the person understood the specific decision in front of them at the specific moment they made it, not what their chart says in general.

That said, a fluctuating or progressive condition is exactly the kind of fact pattern where careful, contemporaneous evidence becomes important, because "was this a good day or a bad day" can become a genuinely contested question later.

Why Documentation of the Moment Matters So Much

Because capacity is assessed at a specific moment, the strength of any later challenge often comes down to what evidence exists about that moment:

• Who was present, and what did they observe about the person's alertness and understanding?
• Was a lawyer involved, and did they take notes about how the person responded to questions?
• Was there a capacity assessment close in time to the decision, rather than months before or after?
• Did the person explain their reasoning in their own words, rather than simply agreeing to something presented to them?

None of this guarantees a decision will withstand a later challenge, but thin or absent evidence about the moment of decision-making is one of the most common weaknesses in these situations.

What This Means for Families

A diagnosis doesn't automatically end someone's right to decide

Family members sometimes assume that once dementia is diagnosed, a person can no longer make any legal decisions. That's not how Ontario law works. The person may still be capable of many decisions — the analysis has to be done decision by decision.

Good-day planning is worth doing early

If a loved one's capacity is expected to decline or fluctuate, it's often better to complete planning documents, such as a will, a Power of Attorney for Property, and a Power of Attorney for Personal Care, as early as possible on a clearly good day, rather than waiting.

A capacity assessment may still be warranted

Where there's real uncertainty or disagreement about someone's capacity for a specific decision, a formal capacity assessment by a qualified assessor can provide clarity and a documented record, something generic family observation can't replace.

Frequently asked questions