Mental capacity can be assessed by a range of professionals depending on the type of decision involved. For medical decisions, any licensed physician, physician assistant, or nurse practitioner is legally permitted to assess and document capacity. For legal and financial decisions, such as making a will or setting up a power of attorney, solicitors and other designated professionals play key roles. The answer depends on what decision is being made and in what context.
Medical Decision-Making Capacity
Any licensed physician (including both MDs and DOs), physician assistant, or advanced-degree nurse practitioner can assess whether a patient has the capacity to make their own medical decisions. This is a core clinical skill, not something reserved for specialists. In practice, the doctor or provider managing your care is usually the one who performs the assessment.
Psychiatrists are sometimes called in for particularly complex or contested cases, but their involvement is not required as a default. Nurses, nursing assistants, technicians, and other support staff are not legally permitted to carry out these assessments due to licensing restrictions. If you’re in a hospital or clinic and a capacity question arises, it will be handled by one of the licensed providers on your care team.
Capacity for Making a Will
When someone is elderly or has experienced a serious illness, solicitors often follow what’s known as the “golden rule”: they arrange for a doctor to examine the person and confirm they have the mental capacity to make a will. This practice comes from a landmark court judgment that recommended the making of a will in these circumstances “ought to be witnessed or approved by a medical practitioner who satisfies himself of the capacity and understanding of the testator, and records and preserves his examination and finding.”
The golden rule isn’t a strict legal requirement in every case, but failing to follow it can leave a will vulnerable to challenge. If you’re helping a relative draft a will and there’s any doubt about their mental state, having a doctor’s assessment on file provides strong legal protection.
Lasting Power of Attorney
Setting up a lasting power of attorney (LPA) requires a certificate provider to confirm that the person creating it (the donor) understands what they’re signing, grasps the scope of decisions they’re handing over, and is not being pressured. The donor chooses this certificate provider, but there are clear rules about who qualifies.
A certificate provider must be 18 or older and falls into one of two categories. They can be someone who has known the donor personally for at least two years, such as a friend, neighbor, or someone from a sports or social club. Alternatively, they can be a professional: a solicitor, barrister, registered social worker, independent mental capacity advocate, or registered healthcare professional like a GP. They cannot be a relative of the donor or attorney, an employee of either party, or someone who works at or manages a care home where the donor lives.
What a Capacity Assessment Actually Tests
Capacity is decision-specific and time-specific. A person isn’t simply “capable” or “incapable” across the board. They may have the capacity to decide what to eat for dinner but lack it for a complex financial decision. Their capacity can also fluctuate, improving or declining depending on their condition at any given time.
Under the Mental Capacity Act, there’s a two-stage test. First, does the person have an impairment of their mind or brain, whether from illness, injury, or external factors like alcohol or drug use? Second, does that impairment prevent them from making this specific decision right now? A person is considered unable to make a decision if they cannot do one or more of the following:
- Understand the information relevant to the decision
- Retain that information long enough to work through it
- Weigh up the information as part of reaching a decision
- Communicate their decision by any means
This is a functional test. It looks at what the person can actually do with the information in front of them, not whether they have a particular diagnosis.
Key Principles Assessors Must Follow
Anyone assessing capacity is bound by a set of guiding principles. The starting point is always a presumption of capacity: every adult is assumed to be able to make their own decisions unless there is evidence to the contrary. Before concluding someone lacks capacity, all practicable steps must be taken to help them make the decision themselves. This could mean simplifying language, using visual aids, choosing a time of day when the person is more alert, or bringing in a familiar person for support.
Making an unwise decision is not the same as lacking capacity. A person who chooses to refuse treatment or spend their savings in ways others disagree with is not automatically incapable. If someone is ultimately found to lack capacity, any decision made on their behalf must be in their best interests and must be the option least restrictive of their rights and freedoms.
Formal Assessment Tools
Most capacity assessments are done through a structured clinical conversation. The assessor talks through the decision with the person, checking whether they can understand, retain, and weigh the relevant information. When that conversation doesn’t produce a clear answer, formal tools can help.
The Aid to Capacity Evaluation (ACE) is a directed clinical interview that walks through all four elements of the capacity test. It’s widely used and designed to keep the assessment objective. The Hopkins Competency Assessment Test (HCAT) is quicker but evaluates generalized incapacity rather than capacity for a specific decision, which makes it less precise in many situations. The MacArthur Competence Assessment Tool for Treatment is another well-established option. Using a formal tool improves accuracy compared to relying on clinical judgment alone.
Cognitive screening tools like the Mini-Mental State Examination or the Montreal Cognitive Assessment are sometimes used alongside a capacity evaluation, but scoring poorly on a cognitive test does not by itself prove someone lacks capacity. Cognition and capacity overlap but are not the same thing. A person with moderate dementia may still retain the capacity for straightforward decisions.
When a Specialist Gets Involved
In straightforward situations, the treating clinician or the relevant professional handles the assessment without outside help. Specialist involvement, typically a psychiatrist or neuropsychologist, becomes appropriate when the case is particularly complex, when the person’s condition fluctuates significantly, or when the assessment is being contested by family members or legal representatives. Court proceedings may also require a specialist report, particularly in cases involving the Court of Protection or disputes over a will.
For day-to-day care decisions in settings like care homes or community services, social workers and care managers often take the lead on identifying when a capacity assessment is needed and coordinating the right professional to carry it out. They may not perform the formal clinical assessment themselves for medical decisions, but they play a central role in the process and may assess capacity for care and welfare decisions within their professional scope.