A retrospective mental capacity assessment is an evaluation conducted after a specific decision has been made, often in the past, to determine whether an individual had the mental capacity to make that decision at the time. Unlike a prospective mental capacity assessment, which assesses an individual's capacity before a decision is made, a retrospective assessment looks back to evaluate whether the person had the requisite mental capacity when the decision was actually made.

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These assessments are typically conducted when there are concerns or disputes about the validity of a decision made by an individual, especially if that decision has legal or significant consequences. For example, a retrospective mental capacity assessment might be performed to determine if an individual had the mental capacity to create a will, make a financial transaction, or provide informed consent for medical treatment at a specific point in the past.