Testamentary Capacity: The Legal Standard for Making a Valid Will

The Banks v. Goodfellow Test

The legal standard for testamentary capacity has remained remarkably consistent since the 1870 English case Banks v. Goodfellow. To validly execute a will, a person must simultaneously satisfy four criteria at the moment of signing:

They must understand the nature of the act. The testator knows they are creating a document that will distribute their property after death.

They must understand the extent of their property. They have a general awareness of what they own — not a precise accounting of every bank balance, but a reasonable grasp of the nature and approximate value of their assets.

They must appreciate the claims of potential beneficiaries. The testator recognizes who would naturally expect to benefit from their estate — spouse, children, dependents — even if they ultimately choose to leave those people nothing.

They must be free from delusions that influence the will. Their judgment cannot be distorted by cognitive disorders, hallucinations, or fixed false beliefs that directly affect the testamentary provisions.

This test applies in the US, UK, Canada, Australia, and New Zealand. Some US states have codified it in statute; others apply it through case law.

Dementia Does Not Automatically Invalidate a Will

One of the most misunderstood aspects of testamentary capacity is its relationship to dementia diagnoses. A medical diagnosis of Alzheimer's disease, vascular dementia, or another cognitive condition does not automatically render a will invalid.

The law recognizes "lucid intervals" — periods when a person with progressive cognitive decline temporarily possesses sufficient understanding to execute a valid legal document. What matters is the testator's mental state at the specific moment of signing, not their general condition.

This means a person with early-stage dementia can execute a valid will during a lucid period, while a person with no formal diagnosis might lack capacity due to temporary confusion, severe illness, or medication effects on the day they signed.

Evidence That Proves Lack of Capacity

Building a capacity challenge requires medical and observational evidence tied to the time the will was executed.

Medical records. Hospital admissions, GP notes, memory clinic assessments, and medication logs from the weeks and months surrounding the signing date. Look specifically for cognitive testing results (MMSE, MoCA scores), documented confusion episodes, and prescriptions for psychoactive medications.

Witness observations. Testimony from people who interacted with the testator around the time of signing — neighbors who noticed confusion, caregivers who documented behavioral changes, or family members who observed disorientation during visits.

The drafting attorney's notes. Notes may record observations about the testator's mental state and independence during instructions. Notes that raise questions can be significant evidence.

Expert medical opinion. A geriatric psychiatrist or neuropsychologist can review the medical record and offer a retrospective assessment of the testator's capacity at the time of execution. These expert reports typically cost $3,000 to $7,000.

The Shifting Burden of Proof

In most jurisdictions, a will that appears properly executed carries a presumption of validity. The person challenging it bears the initial burden of presenting enough evidence to raise a legitimate question about capacity.

Burden-shifting rules vary by jurisdiction and legal ground. A presumption of undue influence can shift the burden to a beneficiary when the claimant establishes a relationship of deep trust and confidence and a transaction that calls for explanation.

Capacity for a Codicil vs. a Will

The same capacity standard applies to codicils — amendments that modify an existing will. Because codicils are frequently executed late in life, often in hospitals or care facilities, they attract a disproportionate share of capacity challenges.

A codicil signed during a period of documented cognitive decline, particularly one that dramatically changes the estate plan in favor of a new caregiver or recently arrived family member, faces heavy scrutiny.

If you suspect a loved one's will was signed when they lacked the mental capacity to understand what they were doing, our Contesting a Will toolkit includes a capacity evidence checklist and a timeline template for organizing medical records against the signing date.