Experienced. Innovative. Responsive.

When does an adult lose their testamentary capacity?

On Behalf of | Mar 20, 2026 | Probate Litigation |

Testamentary capacity is the cognitive and legal ability to enter into binding agreements and draft wills. It requires an understanding of the documents and their implications for the future.

Most people acquire testamentary capacity when they become legal adults on their 18th birthdays. They retain that capacity indefinitely in most cases. However, medical challenges can leave people struggling to manage their own affairs and potentially incapable of entering into binding agreements on their own behalf.

Sometimes, families shocked and disappointed by the terms included in a will can contest the document by claiming that its author lacked the legal capacity necessary to draft a valid document. When do people lose their capacity?

The burden of proof is on the plaintiff

There is no specific age when people lose the capacity to draft or update wills. During a will contest, the party asserting that the testator lacked capacity must prove that assertion to the courts. Doing so requires medical evidence, testimony from others and possibly financial documentation.

To show that the testator lacked testamentary capacity, plaintiffs must prove that they couldn’t truly understand their circumstances. An inability to name their beneficiaries or catalog their assets could be indicative of a lack of capacity.

Expressing an inability to understand the impact the documents might have could also help establish that they lacked capacity. Evidence of the testator having debilitating conditions such as various forms of dementia, severe mental illness and even brain injuries can help support claims that they lacked the capacity to create binding documents at the time when they drafted their will.

Reviewing personal concerns and the timing of a will’s creation can help family members determine if a will contest is possible. Going to court to show a lack of capacity can lead to the court setting aside questionable testamentary instruments.