The Mental Capacity Act exists to protect two things that can pull in opposite directions: a person’s right to make their own decisions, and their safety when they cannot. Its starting point is not “is this person vulnerable?” but “can this person make this decision, at this time?” — and it assumes the answer is yes unless there is good reason to think otherwise.
This guide explains what the Act is, its five principles, how capacity is actually assessed, and what “best interests” means when someone genuinely cannot decide for themselves.
What the Mental Capacity Act is
The Mental Capacity Act 2005 (MCA) has been in force since 2007 and applies in England and Wales. It provides the legal framework for making decisions on behalf of adults (16 and over) who lack the mental capacity to make particular decisions for themselves.
It covers everyday decisions and major ones alike — from what to wear or eat, to where to live, to serious medical treatment and finances. The core idea is that capacity is decision-specific and time-specific: someone may be able to decide what to have for lunch but not manage complex finances, and capacity can fluctuate — present one day, absent the next.
The five principles
Everything in the Act flows from five statutory principles. They are not optional guidance — they are the law, and they must underpin every decision made under the Act.
- Presumption of capacity. Every adult has the right to make their own decisions and must be assumed to have capacity unless it is proved otherwise. The burden is on showing a lack of capacity, never on the person to prove they have it.
- Support to make their own decision. A person must be given all practicable help to make a decision before anyone concludes they cannot — the right information, in the right format, at the right time, in the right place.
- The right to make unwise decisions. A person is not to be treated as unable to decide merely because their decision seems eccentric, risky or unwise to others. Capacity is about the ability to decide, not the wisdom of the choice.
- Best interests. Anything done for a person who lacks capacity must be done in their best interests.
- Least restrictive option. Before the decision is made, the person’s rights and freedom of action must be restricted as little as possible while still achieving the purpose.
These principles matter because they push against the natural instinct to “take over” for someone who seems to be struggling. The Act insists you support first, and only step in when capacity is genuinely absent.
How capacity is assessed — the two-stage test
The Act sets out a two-stage test:
Stage 1 — the diagnostic test. Is there an impairment of, or disturbance in, the functioning of the person’s mind or brain? This might be dementia, a learning disability, a brain injury, a mental health condition, or even a temporary state such as being unconscious or under the influence.
Stage 2 — the functional test. Does that impairment mean the person cannot make this specific decision at this time? A person is unable to make a decision if they cannot do any one of the following:
- Understand the information relevant to the decision
- Retain that information long enough to make the decision
- Use or weigh the information as part of the process
- Communicate their decision (by any means — speech, signs, blinking)
If they cannot do any one of those four, and it is because of the impairment, they lack capacity for that decision. Failing on none of them means they have capacity — and their decision stands, however unwise it looks.
Making a “best interests” decision
Where a person genuinely lacks capacity, any decision made for them must be in their best interests — and that is not the same as what the decision-maker thinks is best. The Act requires you to:
- Consider whether the person may regain capacity, and whether the decision can wait until they do
- Involve the person as fully as possible
- Consider their past and present wishes, feelings, beliefs and values — what would they have wanted?
- Consult family, carers, and anyone with a legal role such as an attorney or deputy
- Not make the decision based merely on the person’s age, appearance, condition or behaviour
- Choose the least restrictive option that meets the need
Best interests is a genuine, evidenced judgement about this person — not a shortcut to the easiest or safest choice for the service.
Lasting Power of Attorney, deputies and advocates
The Act also created the tools for planning ahead and for representation:
- Lasting Power of Attorney (LPA) — lets a person, while they have capacity, appoint someone to make decisions for them if they later lose it (health and welfare, or property and finance).
- Court of Protection deputies — appointed by the court where there is no LPA and ongoing decisions are needed.
- Independent Mental Capacity Advocate (IMCA) — an advocate for people who lack capacity and have no one else to represent them, in certain serious decisions.
How this connects to DoLS
Sometimes protecting a person who lacks capacity means restricting their freedom to the point of a deprivation of liberty — for example, a person with dementia in a care home who is under constant supervision and not free to leave. That cannot simply be done informally; it must be lawfully authorised under the Deprivation of Liberty Safeguards (DoLS), which operate within the Mental Capacity Act framework. See our guide to what DoLS is and when it applies.
Further reading
- Gov.uk — Mental Capacity Act Code of Practice
- SCIE — Mental Capacity Act resources
- Mental Capacity Act 2005
Frequently asked questions
What is the Mental Capacity Act 2005?
The Mental Capacity Act 2005 is the legal framework in England and Wales for making decisions on behalf of adults aged 16 and over who lack the mental capacity to make particular decisions for themselves. Capacity is decision-specific and time-specific — someone may be able to make some decisions but not others, and capacity can fluctuate. The Act has been in force since 2007.
What are the five principles of the Mental Capacity Act?
1) A person must be assumed to have capacity unless proven otherwise. 2) A person must be given all practicable help to make their own decision before being treated as unable to. 3) A person is not to be treated as unable to decide merely because the decision seems unwise. 4) Anything done for a person who lacks capacity must be in their best interests. 5) It must be the least restrictive option for their rights and freedom.
How is mental capacity assessed?
Through a two-stage test. Stage one: is there an impairment of, or disturbance in, the functioning of the mind or brain? Stage two: does that impairment mean the person cannot make this specific decision at this time? A person is unable to decide if they cannot understand, retain, use or weigh the relevant information, or communicate their decision. Failing any one of those four, because of the impairment, means they lack capacity for that decision.
What does ‘best interests’ mean under the Mental Capacity Act?
It means a genuine, evidenced judgement about what is right for that particular person — not simply what the decision-maker thinks is best. It requires involving the person as far as possible, considering their past and present wishes, feelings, beliefs and values, consulting family and anyone with a legal role, avoiding assumptions based on age or condition, and choosing the least restrictive option that meets the need.
Can someone make an unwise decision under the Mental Capacity Act?
Yes. The third principle is explicit that a person is not to be treated as unable to make a decision merely because it appears eccentric, risky or unwise to others. Capacity is about the ability to make the decision, not the wisdom of the choice. If a person has capacity, their decision stands even if others disagree with it.
Mental Capacity Act training
Our Mental Capacity Act course covers the five principles, the two-stage capacity test, best-interests decision-making, and the roles of LPAs, deputies and advocates.
Related: What is DoLS? · Deprivation of Liberty Safeguards (DoLS) · What is person-centred care? · Dementia awareness
£9 per course. CPD accredited, 100 % online, verifiable e-certificate on completion. Pay for 2, get 3 — any 3 courses for £18.
Please note: this is a CPD-accredited awareness course and general information, not legal advice. The Mental Capacity Act applies in England and Wales; Scotland and Northern Ireland have their own frameworks. Where a specific capacity or best-interests decision is complex or contested, seek advice from the appropriate professional or the Court of Protection. It is not an Ofqual-regulated qualification.