Lack of Testamentary Capacity: Proving a Will-Maker Couldn't Understand

The Legal Standard for Mental Capacity

Testamentary capacity is the minimum level of mental understanding required to make a valid will. It's a legal standard, not a medical one — and the distinction matters. A person can have dementia, take heavy medication, or need help with daily tasks and still possess the legal capacity to sign a will, as long as they meet the test at the exact moment of execution.

The standard used across the U.S., UK, Canada, Australia, and most common-law countries originates from the 1870 English case Banks v. Goodfellow. The testator must simultaneously satisfy four conditions:

1. Understand the nature of the act — they must know they're making a document that distributes their property after death
2. Know the extent of their property — they need a general awareness of what they own, not a precise inventory
3. Appreciate who has claims on them — they must understand who their natural beneficiaries are (spouse, children, dependants) even if they choose to leave them nothing
4. Be free from delusions that affect the will — they must not be operating under false beliefs that distort their decisions about distribution

All four must be present at the moment of signing. This is what makes capacity challenges so fact-specific — a person might meet all four criteria at 10 a.m. and fail to meet them by 3 p.m.

Why This Ground Succeeds More Often Than Others

Lack of testamentary capacity is the most commonly raised and most frequently successful ground for contesting a will. Several factors make it stronger than alternatives like undue influence or fraud:

Medical evidence is concrete. Unlike undue influence — which requires proving the subjective mental state of both the testator and the influencer — capacity claims rely on objective medical records. Hospital notes, cognitive test results, medication logs, and specialist diagnoses provide the kind of evidence courts find persuasive.

The demographic reality supports it. As life expectancies rise, more people live long enough to experience cognitive decline. A growing proportion of wills are executed or amended during the late stages of life, often when dementia, Alzheimer's, or other cognitive conditions are present.

Courts take it seriously. Judges understand that vulnerable adults can be exploited by people around them. When medical evidence shows significant cognitive impairment at or near the date a will was signed, courts apply heightened scrutiny.

What a Dementia Diagnosis Does (and Doesn't) Prove

A diagnosis of dementia, Alzheimer's disease, or another cognitive condition does not automatically invalidate a will. Courts recognize that degenerative conditions progress at different rates, that many patients experience lucid intervals of varying duration, and that the legal threshold for capacity is relatively low — lower than the capacity required for entering a contract or managing finances.

This means the medical records must do more than show a diagnosis. They need to demonstrate the severity and specific impact of the condition at the time the will was executed. Key evidence includes:

• Cognitive assessment scores (MMSE, MoCA) from the period surrounding the will's execution date
• Clinical notes describing confusion, disorientation, failure to recognize family members, or inability to manage basic tasks
• Medication records showing psychoactive drugs that may have affected cognition
• Care home or hospital observation logs documenting day-to-day cognitive functioning
• Testimony from the solicitor who drafted the will about the testator's engagement and understanding during the meeting

The most powerful evidence is a cognitive assessment conducted close to the execution date that shows scores inconsistent with understanding the Banks v. Goodfellow criteria.

The "Golden Rule" for Will Preparation

In the UK, the "golden rule" (established in Kenward v. Adams) holds that when a solicitor prepares a will for an elderly or seriously ill testator, they should obtain a medical opinion confirming the testator's capacity before the will is executed. This isn't a legal requirement — a will made without following the golden rule isn't automatically invalid — but failure to follow it raises questions.

When the golden rule was followed and a doctor confirmed capacity, challengers face a steeper climb. When it wasn't followed, particularly for a testator with known cognitive issues, courts are more receptive to capacity challenges.

Several U.S. states encourage similar practices, though the terminology varies.

Lucid Intervals: The Defense's Strongest Argument

The executor defending the will typically argues that even a person with progressive dementia can experience lucid intervals — periods of clarity during which they understand their situation and can make rational decisions. If the will was executed during such an interval, it's valid regardless of the testator's general decline.

Overcoming a lucid interval defense requires evidence specifically tied to the execution date:

• What do the medical records show for that exact day or week?
• Was the testator able to engage meaningfully with the attorney during the drafting meeting?
• Did the testator independently identify their assets and heirs, or were they prompted?
• Are there witness accounts of confusion or disorientation around the same date?

The closer your evidence gets to the moment of signing, the more it undermines a lucid interval claim.

Building Your Case

If you believe a will was signed when the testator lacked capacity, the evidence-gathering process should start immediately:

Request complete medical records from all providers who treated the deceased — primary care, specialists, hospitals, and care facilities. Focus on the period surrounding the will's execution date, but request the full history to show the trajectory of decline.

Identify the drafting solicitor or attorney and request their file notes from the will preparation. These often contain observations about the testator's mental state during the meeting.

Interview people who had regular contact with the deceased — neighbors, friends, caregivers, clergy — about their observations of cognitive function.

Consider a retrospective capacity assessment. A geriatric psychiatrist can review the medical records and other evidence to render an expert opinion on whether the testator met the Banks v. Goodfellow criteria. These assessments cost $3,000 to $7,000 and often form the centerpiece of the challenger's case.

The Contesting a Will toolkit includes an evidence tracker designed specifically for capacity cases — organizing medical records, witness observations, and timeline events into the framework courts use to evaluate these claims.