Testamentary capacity is typically assessed at the specific moment the will was executed, not by the testator's general mental state over time, and the standard is usually described as requiring the testator to understand the nature and extent of their property, know the natural objects of their bounty (close family members who might expect to inherit), understand that they are making a document that distributes property at death, and be able to relate these elements to form an orderly plan. This is deliberately a lower bar than the capacity required to manage finances or enter contracts, reflecting the law's general preference for honoring a person's testamentary wishes where reasonably possible.

A diagnosis of dementia, mental illness, or cognitive decline does not automatically defeat testamentary capacity — courts have repeatedly found that a person can lack capacity for some purposes while retaining sufficient capacity to make a will, particularly during a lucid interval. Capacity challenges typically rely on medical records, testimony from witnesses present at execution (including the attorney who supervised signing), and expert evaluation, with the timing of any evidence relative to the actual signing date being critical.

Juricratic models testamentary capacity as a threshold probability dial informed by the medical and witness evidence a user inputs, reflecting that capacity findings are fact-intensive and time-specific rather than a fixed conclusion drawn from a diagnosis alone.

Estate planning attorneys supervising execution of a will for an elderly or ill client routinely document capacity contemporaneously — noting the client's demeanor, responses to capacity-related questions, and sometimes obtaining a physician's capacity evaluation near the signing date — precisely because that contemporaneous record is often the deciding evidence if capacity is later challenged.