When someone close to you begins having difficulty with decisions, it’s easy to imagine that there must be a formal moment when a doctor declares that they have “lost capacity”.
That can sound frightening. It suggests that one assessment might suddenly take control away from them.
In reality, the law does not work like that. There is no single certificate declaring that a person either has or does not have mental capacity, and there is no rule that only a doctor can assess it.
Capacity is about a particular decision, at a particular time. Someone may be perfectly able to decide what they want to eat, where they want to go or how they spend ordinary amounts of money, while being unable to understand a much more complicated decision about medical treatment or selling their home.
Quick answer: A mental capacity assessment does not always have to be carried out by a doctor or other healthcare professional. Anyone can assess capacity if they are an appropriate person to assess the particular decision. For an everyday decision, that might be a family member or carer. For medical treatment, it will usually be the healthcare professional responsible for the treatment. For an important financial, welfare or legal decision, a more formal assessment and professional input may be needed.
During my years in practice, I found that one of the least helpful questions was often the broadest one: “Does this person have capacity?” The answer nearly always begins with another question: capacity to decide what?
This guide explains how the law approaches that question in England and Wales. For related guidance on wills, powers of attorney and planning ahead, see my lifetime planning guides.
Contents
- Who can carry out a mental capacity assessment?
- When should mental capacity be assessed?
- How is mental capacity assessed?
- What help must be given before deciding somebody lacks capacity?
- Does a mental capacity assessment need to be carried out by a doctor?
- What if mental capacity fluctuates?
- Does a mental capacity assessment have to be recorded?
- What happens if somebody lacks capacity?
- Can a mental capacity assessment be challenged?
- Frequently asked questions
Who can carry out a mental capacity assessment?
There is no single profession with an exclusive legal right to assess mental capacity. A doctor is not automatically required, nor is there a universal qualification called a “mental capacity assessor”.
The person carrying out the assessment should, however, be appropriate to the decision being considered.
For ordinary day-to-day decisions, that might be a relative, friend, carer or support worker. Nobody needs to call a psychiatrist because someone is choosing what to wear or what they would like for lunch.
Where medical treatment is proposed, the healthcare professional responsible for that treatment will ordinarily need to consider whether the patient can consent to it. A social worker or other suitably experienced professional may assess capacity in relation to care or accommodation. Lawyers and other advisers may also need to consider capacity when dealing with decisions for which they are professionally responsible.
The Government’s guidance on assessing mental capacity makes the position clear: anyone can assess capacity, but the assessor should be someone appropriate to the particular decision or action.
The seriousness of the decision matters. An informal assessment may be perfectly adequate for something routine. If the decision involves major medical treatment, substantial finances, a move into care or another important change in somebody’s life, much greater care may be needed in deciding who should carry out the assessment and how it should be recorded.
When should mental capacity be assessed?
The starting point under the Mental Capacity Act 2005 is that a person must be assumed to have capacity unless it is established that they do not.
That is more than a legal technicality. It means you should not assume that somebody cannot make their own decisions because they are elderly, disabled, living with dementia, have suffered a brain injury or behave in a way that other people find unusual.
Nor does making a bad decision prove a lack of capacity. We are all allowed to make choices other people think are unwise.
An assessment becomes appropriate where there is a genuine reason to doubt whether the person can make the particular decision in front of them. Perhaps they cannot understand what is being proposed even after it has been carefully explained. They may understand initially but be unable to retain the essential information long enough to decide. They may be able to repeat the options but be unable to use or weigh them when reaching a choice.
Sometimes the concern is temporary. Delirium, the effects of medication, acute illness or the aftermath of a stroke may interfere with decision-making for a period without permanently removing the person’s ability to decide for themselves.
The Mental Capacity Act framework discussed in this guide generally applies to people aged 16 and over. Some specific legal decisions and arrangements have their own rules and age requirements.
How is mental capacity assessed?
The assessment must begin with the actual decision.
It is not enough to ask whether somebody has “general capacity”, whether their memory is poor or whether they have a particular diagnosis. The assessor needs to identify what the person is being asked to decide and the information that is relevant to that decision.
Under sections 2 and 3 of the Mental Capacity Act 2005, a person lacks capacity in relation to a matter if, at the relevant time, they are unable to make the decision because of an impairment of, or disturbance in the functioning of, their mind or brain.
In practical terms, the assessor needs to consider whether the person is unable to make the particular decision and, if so, whether that inability is caused by an impairment or disturbance of the mind or brain.
A person is unable to make a decision if they cannot:
- understand the information relevant to the decision;
- retain that information long enough to make the decision;
- use or weigh that information as part of making the decision; or
- communicate their decision by any means.
The connection between the inability and the impairment matters. A diagnosis of dementia, depression, a learning disability or brain injury does not itself establish incapacity. The impairment or disturbance must cause the person’s inability to make the particular decision.
Relevant information will depend on the decision. It will usually include the nature of the decision, the realistic options and the reasonably foreseeable consequences of deciding one way or another, including the consequences of doing nothing.
The person does not need to understand every technical detail. Someone deciding whether to undergo an operation does not need the surgeon’s medical knowledge. They need enough understanding of the proposed treatment, its important risks and benefits, reasonable alternatives and the consequences of refusing it to be able to make their own choice.
Nor must information be retained indefinitely. The Act specifically recognises that being able to hold relevant information for only a short period does not by itself mean that the person lacks capacity. The question is whether they can retain it for long enough to use it in making the decision.
Lack of capacity must be established on the balance of probabilities. It is not enough simply to suspect it.
The Government provides a useful shorter explanation in its guidance on checking mental capacity.
What help must be given before deciding somebody lacks capacity?
A mental capacity assessment should not feel like an exam that the person is expected to pass unaided.
Before concluding that somebody cannot make a decision, all practicable steps must be taken to help them make it themselves. In real life, those steps can make a considerable difference.
Information may need to be explained in simpler language, broken into smaller parts or presented using pictures or another accessible format. Someone with hearing difficulties may need appropriate equipment. A person who communicates in a different way may need more time or specialist assistance.
The surroundings can matter too. A familiar, quiet room may be better than a busy hospital ward. Somebody may think more clearly at a particular time of day, or before rather than after medication. A trusted relative may help one person feel relaxed while making another reluctant to speak openly.
This is one reason I dislike the idea of capacity assessment as a box-ticking exercise. How you ask the question can affect whether the person is actually able to answer it.
The NICE guidance on decision-making and mental capacity provides detailed guidance on supporting people to make their own decisions and carrying out proportionate assessments.
Does a mental capacity assessment need to be carried out by a doctor?
No. There is no general rule requiring a doctor to assess mental capacity.
There are, however, situations where medical or other specialist input is sensible and sometimes essential to obtaining reliable evidence.
If the decision is particularly serious, the person’s difficulties are complex, there is disagreement about their capacity or the assessment is likely to be challenged, a professional with suitable expertise may be needed. Specialist involvement may also be important where communication difficulties or a particular medical, neurological or psychological condition make assessment more complicated.
That professional will not necessarily be a GP or psychiatrist. Depending on the question, useful expertise may come from a psychologist, social worker, occupational therapist, speech and language therapist or another practitioner who understands the person’s condition and the decision being assessed.
Court proceedings may require more formal evidence. For example, some Court of Protection applications use the COP3 assessment of capacity.
The important point is to match the assessment to the decision rather than simply trying to obtain a generic declaration that somebody “has lost capacity”.
What if mental capacity fluctuates?
Capacity can change over time, and sometimes over quite short periods.
A person affected by delirium, medication, some mental health conditions, dementia or the aftermath of a stroke may be much better able to make a decision at one time than another.
If the decision can safely wait and the person is likely to regain the ability to make it, postponing the decision may allow them to decide for themselves. Equally, an assessment carried out some months ago should not automatically be treated as proving that the person lacks capacity for a different decision today.
Where capacity regularly fluctuates, timing the discussion carefully and recording the circumstances of the assessment can become particularly important.
Does a mental capacity assessment have to be recorded?
There is no universal form that must be completed every time somebody considers whether another person can make a decision.
For ordinary day-to-day matters, a formal written assessment may be unnecessary. The position is very different where a professional is making an important decision, a person has been assessed as lacking capacity, substantial financial or welfare interests are involved, or disagreement is likely.
In those circumstances, there should be a clear record of what decision was being assessed, what information was relevant, what was done to help the person decide, the evidence considered and why the assessor reached their conclusion. Health and social care professionals are expected to keep appropriate records, particularly where somebody has been found to lack capacity.
A careful record protects the person whose autonomy is at stake as much as it protects the assessor. It also makes it possible for somebody else to understand and, if necessary, question how the conclusion was reached.
What happens if somebody lacks capacity?
A finding that somebody lacks capacity does not hand another person general control over their life.
First, the finding relates only to the particular decision assessed. Secondly, the person making any decision on their behalf must have legal authority to do so.
That might be an attorney acting under a valid Lasting Power of Attorney, a deputy appointed by the Court of Protection, a healthcare professional making a treatment decision or another person acting within the Mental Capacity Act framework.
A husband, wife, civil partner, son or daughter does not automatically acquire legal authority over somebody’s finances, medical treatment or welfare simply because they are the closest relative.
If an attorney has already been appointed, their authority depends upon the type and terms of the LPA. My separate guide explains how Lasting Powers of Attorney work.
Where a decision is made for somebody under the Mental Capacity Act, it must be made in their best interests. The person should still be encouraged to participate as fully as possible. So far as they can reasonably be ascertained, their past and present wishes and feelings, beliefs and values must be considered. Where it is practicable and appropriate, the decision-maker should also consult relevant people who know or care for them. Any option that is less restrictive of the person’s rights and freedom should be considered.
There are also some highly personal decisions that the Mental Capacity Act does not allow somebody else to make on a person’s behalf. These include consenting to marriage or civil partnership and consenting to sexual relations.
Medical decisions require another check. A person may previously have made a valid and applicable Advance Decision to Refuse Treatment or appointed health and welfare attorneys with relevant authority. My guide to living wills and Advance Decisions to Refuse Treatment explains that separate area.
Serious disputes about capacity or best interests can ultimately be determined by the Court of Protection.
Can a mental capacity assessment be challenged?
Yes. A professional opinion is important evidence, but the assessor’s job title does not make the conclusion unchallengeable.
If there is concern about an assessment, it is often useful to start by asking exactly what decision was assessed, what information the person was expected to understand and why the assessor concluded that they could not understand, retain, use or weigh that information, or communicate their decision.
Sometimes the real disagreement is not about capacity at all. It is simply that relatives or professionals strongly disagree with the decision the person has made. That is where the protection for unwise decisions matters most.
In other cases, another assessment may be appropriate, particularly where capacity fluctuates, communication was difficult or specialist expertise could change the picture. Complaints procedures, meetings or mediation may help resolve disagreements. Where a serious dispute cannot be settled, the Court of Protection can decide whether the person has capacity to make the particular decision.
Frequently asked questions
Can a family member assess mental capacity?
Yes, where they are an appropriate person to consider the decision involved. Family members and carers routinely have to think about capacity in relation to ordinary day-to-day decisions.
That does not necessarily make a relative the right person to provide formal evidence about a major medical, financial or welfare decision. The more serious or disputed the issue, the stronger the case for an appropriately experienced professional assessment.
Does dementia automatically mean somebody lacks mental capacity?
No. A dementia diagnosis does not itself establish lack of capacity.
The person must be considered in relation to the particular decision at the time it needs to be made. Someone living with dementia may retain capacity for many decisions, and their ability to decide may fluctuate.
Can somebody with capacity make a bad decision?
Yes. The Mental Capacity Act specifically provides that a person must not be treated as unable to make a decision merely because they make an unwise one.
I appreciate why that can be difficult for families. Watching someone you care about make a choice you think is plainly wrong can be worrying and frustrating. The law nevertheless protects their right to make that choice unless the test for lack of capacity is actually met.
Does having a Lasting Power of Attorney mean that the donor lacks capacity?
No. Making an LPA does not mean somebody has lost capacity.
A property and financial affairs attorney may, if the LPA allows it, act with the donor’s permission while the donor still has capacity. A health and welfare attorney can make a particular decision only when the donor lacks capacity to make that decision themselves.
Is capacity to make a will assessed under the Mental Capacity Act?
Capacity to make a valid will is a specialist area and should not simply be treated as another ordinary Mental Capacity Act assessment. The longstanding common law test in Banks v Goodfellow remains central when the validity of a will is considered.
Someone may lack capacity to deal with complicated financial affairs yet still have the testamentary capacity needed to make a will. My separate guide to writing a valid will in England and Wales explains the relevant test in its proper context.
Start with the decision, not the diagnosis
If there is one question worth remembering, it is not “Does this person have capacity?” It is “Can this person make this particular decision now?”
That may sound like a small distinction, but it changes the whole approach. It stops a diagnosis, an age or one difficult decision becoming a label applied to everything the person does.
A medical condition may be highly relevant. So may professional evidence and the observations of people who know the person well. None of those things replaces the need to identify the decision, support the person to make it and apply the legal test properly.
For me, that is the most important principle running through this area of law. A capacity assessment should not begin by asking how much independence somebody has lost. It should begin by asking what they can still decide for themselves, and what help might enable them to keep doing so.
Last legally reviewed: 5 September 2026
This guide is based on general principles of English and Welsh law, is intended for informational purposes only, and does not constitute legal advice or establish a professional relationship.
