Testamentary capacity is the legal and mental ability of a person making a will (the testator) to make a legally binding disposition of their assets and to understand the nature and effect of the act of making a will—including disposing of their assets at death.

Proof of testamentary capacity is a required element of a will being admitted to probate and recognized by the court as having legal effect.

Adults are generally presumed to have the legal capacity to make a will, but minors (persons under a certain age) are not—with some exceptions in some states, such as if the minor has served in the military or has been married.

Persons who suffer from dementia, Alzheimer’s disease, or insanity, for example, may lack testamentary capacity to make a will.

In legal jargon, the historical terms of art for testamentary capacity were that the testator was “of sound mind and memory” or “of sound mind and disposing memory,” and this terminology is sometimes recited in a will as a statement of the testator regarding the testator’s mental capacity when making the will.

Laws vary from state to state and the requirements related to testamentary capacity are often located in a state’s statutes—usually in the estates code or probate code—and interpreted and applied by the courts in specific factual circumstances or cases that are reported in court opinions involving will contests, for example.

In Arizona, testamentary capacity is the legal and mental ability of a person to create a valid will. This capacity requires the individual, known as the testator, to understand the nature of making a will, the extent of their assets, and the implications of distributing those assets upon death. Arizona law presumes that adults have the necessary testamentary capacity to execute a will. However, minors typically do not have this capacity unless they meet certain exceptions, such as being married or having served in the military. Individuals with mental impairments, such as dementia or Alzheimer's disease, may be deemed to lack the requisite capacity to make a will. The concept of being 'of sound mind and memory' is a traditional legal standard for testamentary capacity and may be included in the language of a will. The specific requirements for testamentary capacity in Arizona are found in the state's probate code and are interpreted by courts in cases involving will contests. It is important for a will to be executed properly to be admitted to probate and recognized as legally effective.