Mental capacity assessments explained: who does them and what happens

A mental capacity assessment checks whether a person can make a specific decision at the time it needs to be made, such as moving into a care home or managing their money. Under the Mental Capacity Act 2005, the assessment is done by whoever is responsible for that decision, often a social worker, doctor or nurse, and it asks whether the person can understand, retain and weigh up the information and communicate a choice. If they cannot, because of an impairment of the mind or brain, the decision must be made in their best interests.

In short

• The Mental Capacity Act 2005 applies in England and Wales to everyone aged 16 or over and starts from the presumption that a person has capacity.
• Capacity is decision-specific and time-specific: your parent may be able to choose what to wear but not to sell their house, and capacity can change from day to day.
• The test has two parts: can the person make the decision (understand, retain, use or weigh, communicate), and if not, is that because of an impairment of the mind or brain.
• Making an unwise decision is not proof of lacking capacity (section 1(4)).
• If someone lacks capacity, decisions must follow the best interests checklist in section 4, and family must be consulted.
• An Independent Mental Capacity Advocate (IMCA) must be appointed for a care home move likely to last 8 weeks or more, or a hospital stay of 28 days or more, if there is no family or friend to consult.

The five principles of the Mental Capacity Act

Section 1 of the Act sets out five principles that every assessor and decision-maker must follow:

1. Assume capacity. A person must be assumed to have capacity unless it is shown that they lack it. A dementia diagnosis alone does not change this.
2. Support first. A person is not treated as unable to decide until all practicable steps to help them have been tried without success.
3. Unwise is not incapable. A person is not treated as lacking capacity merely because they make an unwise decision.
4. Best interests. Anything done for someone who lacks capacity must be done in their best interests.
5. Least restrictive option. Before acting, consider whether the purpose can be achieved in a way that restricts the person’s rights and freedom less.

These principles matter in everyday care. A parent with early signs of dementia who refuses a carer is often still entitled to make that choice, even if the family thinks it is risky. Our guide to dementia and refusing care covers how to respond.

The two-stage test

Sections 2 and 3 set out how capacity is assessed. Since the Supreme Court’s 2021 judgment in A Local Authority v JB, assessors usually ask the functional question first.

Stage 1: Can the person make the decision?

Under section 3, a person is unable to make a decision if they cannot do one or more of these four things:

• understand the information relevant to the decision, including the likely consequences of each option and of not deciding;
• retain that information long enough to make the decision (a short time is enough);
• use or weigh the information as part of the process of deciding;
• communicate the decision by any means, including speech, writing, sign language, gestures or blinking.

Stage 2: Is that because of an impairment of the mind or brain?

Under section 2, the inability must be because of an impairment of, or disturbance in the functioning of, the mind or brain. Examples include dementia, a stroke, a brain injury, a learning disability, a severe mental illness, or temporary confusion from delirium or an infection. There must be a clear link between the impairment and the inability to decide. If a parent cannot weigh up a care home move because they are frightened and grieving, not because of their dementia, they may still have capacity.

Who carries out a capacity assessment

There is no single “capacity assessor” job. The person who needs the decision made is responsible for assessing capacity for that decision. In practice:

For complex or disputed decisions, the assessor may ask a psychiatrist, psychologist or speech and language therapist for specialist input. Families cannot carry out a formal assessment for these decisions, but they have a crucial role in providing information about the person’s history, values and how they communicate best.

What happens during an assessment

A good assessment is a conversation, not an exam. The Mental Capacity Act Code of Practice expects the assessor to:

• tell the person what decision is being considered, using simple language, pictures or written notes;
• pick a time and place when the person is at their best, for example morning rather than late afternoon if they experience sundowning;
• involve someone the person trusts, if they want that;
• address hearing, sight or language barriers, including interpreters;
• explain the realistic options and their consequences, including the option of not deciding;
• record the outcome, the reasons and the steps taken to support the person.

Assessments are usually not one-off. If your parent’s capacity fluctuates, the assessor may visit more than once or wait until confusion from a urinary infection or delirium has cleared, if the decision can wait.

If the person lacks capacity: best interests

When an assessment finds the person lacks capacity for a decision, someone must decide in their best interests. Section 4 lists what must be considered, including the person’s past and present wishes and feelings, their beliefs and values, and the views of family, carers and anyone they have named. Their age, appearance or condition must not be used to make assumptions.

If the person has a valid Lasting Power of Attorney for that type of decision, the attorney makes the decision. If there is no attorney, the professional responsible decides, after consulting the family. Where decisions about property and money are needed regularly and there is no attorney, a Court of Protection deputy may be appointed.

Some best interests decisions also amount to a deprivation of liberty, for example where a person is under continuous supervision in a care home and not free to leave. That needs a separate legal authorisation; see DoLS in care homes. Our guide to whether someone can be forced into a care home explains how these rules work together.

Worked example

Margaret, 84, has moderate Alzheimer’s and lives alone. After two falls, the social worker assesses her capacity to decide where to live. Margaret understands she has fallen but cannot retain the information about the risks for more than a minute, and keeps saying she has never fallen. The social worker records that she lacks capacity for this decision because of her dementia. A best interests meeting with her son and daughter weighs her strong wish to stay at home against the risk. They agree a trial of 24-hour live-in care rather than a care home move, as the less restrictive option. Margaret’s capacity to choose her own clothes and meals is unaffected.

Independent Mental Capacity Advocates

An Independent Mental Capacity Advocate, or IMCA, represents a person who lacks capacity and has nobody appropriate, other than paid carers, to consult about their best interests. The council or NHS body must instruct an IMCA before:

• arranging a care home stay likely to last 8 weeks or more, or a hospital stay likely to last 28 days or more (sections 38 and 39);
• serious medical treatment provided by the NHS (section 37).

Councils and NHS bodies can also instruct an IMCA for care reviews where there is nobody appropriate to consult, and in adult safeguarding cases even where family are involved. If you are the main family member and disagree with professionals, ask whether the person also qualifies for a Care Act advocate, which is a separate right.

How to challenge a capacity assessment

Assessments can be wrong. Common problems include assuming incapacity because of a diagnosis, testing the wrong decision, not giving the person enough support, or confusing an unwise choice with incapacity. If you disagree:

1. Ask for the written assessment. It should name the decision, the four functional tests and the evidence for each.
2. Put your concerns in writing to the assessor or their manager, with specific examples, such as a better time of day or a missing hearing aid.
3. Request a reassessment, or a second opinion from another professional.
4. Use the complaints process of the council or NHS trust, then the Local Government and Social Care Ombudsman or Public Service Ombudsman (formerly the Parliamentary and Health Service Ombudsman).
5. Apply to the Court of Protection for a declaration on capacity in serious disputes. Seek legal advice first; legal aid may be available in some cases.

Scotland and Northern Ireland

The Mental Capacity Act 2005 covers England and Wales. Scotland uses the Adults with Incapacity (Scotland) Act 2000, with similar principles but different procedures, such as guardianship orders from the sheriff court. Northern Ireland has the Mental Capacity Act (Northern Ireland) 2016, which is being brought into force in stages.

Frequently asked questions

Who can do a mental capacity assessment?

The person responsible for the decision assesses capacity for it. That might be a care worker for daily care, a doctor for treatment, or a social worker for a care home move. For a Court of Protection deputyship, a doctor or other qualified practitioner completes form COP3. Families give vital information but cannot carry out formal assessments.

Does a dementia diagnosis mean someone lacks capacity?

No. Section 1 of the Mental Capacity Act 2005 says everyone is assumed to have capacity unless it is shown otherwise. Many people with dementia can make some decisions for years. Capacity must be assessed for each decision at the time it is needed, and the person must be given all practicable help to decide.

What are the four questions in a mental capacity assessment?

Under section 3 of the Mental Capacity Act, the assessor asks whether the person can understand the relevant information, retain it long enough, use or weigh it to reach a decision, and communicate that decision by any means. If they cannot do any one of these because of an impairment of the mind or brain, they lack capacity for that decision.

Can a family member request a mental capacity assessment?

Yes. You can ask the GP, social worker or care home to assess capacity for a specific decision, such as managing money or moving home. Explain what decision is needed and why you are worried. A solicitor can also arrange a capacity report, for example before making a Lasting Power of Attorney.

How do I challenge a mental capacity assessment?

Ask for the written assessment, then write to the assessor or their manager with specific concerns and request a reassessment or second opinion. If that fails, use the council or NHS complaints process and then the ombudsman. In serious disputes, the Court of Protection can make a declaration about capacity.

When is an IMCA needed?

An Independent Mental Capacity Advocate must be instructed when a person lacks capacity, has no family or friend appropriate to consult, and faces serious medical treatment, a care home stay likely to last 8 weeks or more, or a hospital stay likely to last 28 days or more, under sections 37 to 39 of the Act.

Sources

• Mental Capacity Act 2005, section 1: the principles
• Mental Capacity Act 2005, section 2: people who lack capacity
• Mental Capacity Act 2005, section 3: inability to make decisions
• Mental Capacity Act 2005, section 4: best interests
• Mental Capacity Act 2005, section 38: IMCA for NHS accommodation
• GOV.UK: Mental Capacity Act Code of Practice
• GOV.UK: Court of Protection

General information, not legal or financial advice. Figures for 2026/27, checked October 2026.

Reviewed by The Care Panel team on 29 October 2026. This guide is general information about care in England, not legal, medical or financial advice. Rules and rates change; check with your council or an adviser before making decisions.