What is testamentary capacity and why does it matter?

On Behalf of | Jan 16, 2026 | Wills

In order to draft an estate plan or write a will, a person has to have testamentary capacity to do so. This generally refers to their mental capacity and their understanding of the decisions that they are making. A person who makes an estate plan has to be of sound mind, as they are making crucial legal decisions that can affect themselves, their estate, their beneficiaries and their family members.

This can be called into question for many different reasons. For instance, a person who is under the influence of alcohol or drugs may not have the mental capacity to write a will. This could even be true if someone is getting medical treatment that requires them to use certain painkillers or other prescription drugs. The side effects of those drugs can influence the way that they think and the choices they make.

Additionally, certain mental conditions could mean that a person loses their testamentary capacity over time. Common examples include dementia and Alzheimer’s. Someone may be able to draft a will before a diagnosis, but it can become more difficult afterward.

Challenging the estate plan

Testamentary capacity is important because a lack of it may lead to an estate challenge.

For example, say that an elderly person writes a will and leaves out one of their adult children. Did they mean to disinherit that person? Other beneficiaries may say that it was an intentional choice, but the disinherited beneficiary may claim that the elderly person was suffering from Alzheimer’s and simply forgot to include them. This can lead to complex estate challenges that affect how assets are distributed.

When making an estate plan or addressing some of these common conflicts and disputes, it is crucial that all involved understand their legal options.