A parent with dementia refuses to let anyone help with their finances, even though bills are going unpaid. An adult with a learning disability wants to move in with a partner their family is worried about. A patient with a brain injury can’t communicate a decision about their own treatment. In every one of these situations, someone needs to work out a genuinely difficult question: can this person make this decision for themselves, and if not, who decides, and how?
That’s exactly what the Mental Capacity Act 2005 exists to answer. It’s one of the most important pieces of legislation for families, carers and healthcare professionals in England and Wales, yet it’s often only encountered in a crisis — when a decision needs to be made quickly and nobody’s sure what the rules actually are.
This guide explains what the Act covers, the five principles that sit at its core, how capacity is actually assessed, and what options exist for planning ahead before a crisis happens.
What Is the Mental Capacity Act 2005?
The Mental Capacity Act 2005 (MCA) applies in England and Wales and sets out the legal framework for making decisions on behalf of people aged 16 and over who may lack the mental capacity to make a specific decision for themselves. Scotland has its own separate legislation (the Adults with Incapacity Act), so the details below apply specifically to England and Wales.
The Act was designed to replace an old, more paternalistic approach where a diagnosis alone — such as dementia or a learning disability — was often treated as reason enough to take decisions away from someone entirely. The MCA’s central shift is that capacity is decision-specific and time-specific: someone might lack capacity to manage a complex pension transfer but still have full capacity to decide what to eat for dinner or who they want to see.
The Act covers decisions ranging from everyday choices (what to wear, what to eat) through to significant ones (medical treatment, where someone lives, managing their finances), and it’s overseen in practice by the Court of Protection, which can appoint deputies and resolve disputes when informal routes don’t work.
The Five Core Principles
Every decision made under the Act must be guided by five statutory principles. These aren’t just background philosophy — they’re legally binding, and any decision made on someone else’s behalf can be challenged if it doesn’t follow them.
1. A person must be assumed to have capacity unless it’s established that they lack it. Capacity is the starting point, not something a person has to prove they have. A diagnosis of dementia, autism, or a mental health condition does not automatically mean someone lacks capacity for any given decision.
2. A person must be given all practicable support to help them make a decision before it’s concluded they can’t. This might mean using simpler language, choosing a better time of day when someone’s more alert, or involving a communication aid — capacity assessments shouldn’t happen after a token, five-minute attempt.
3. A person is not to be treated as lacking capacity simply because they make an unwise decision. This is one of the most important — and most misunderstood — principles. An adult with full capacity is entitled to make choices others disagree with, including ones that carry real risk, as long as they understand the decision and its consequences.
4. Anything done on behalf of someone who lacks capacity must be done in their best interests. This isn’t the same as doing what’s easiest, or what a family member would prefer — the Act sets out a specific process for working out best interests, covering the person’s own wishes, feelings, values and beliefs, wherever these can be established.
5. Before the decision is made, consider whether the outcome could be achieved in a way that’s less restrictive of the person’s rights and freedom of action. If there’s a way to support someone’s independence while still keeping them safe, that option should be preferred over one that takes more control away than necessary.
How Capacity Is Actually Assessed
Capacity assessments aren’t a single test — they’re specific to the decision being made, and follow a two-stage process set out in the Act.
Stage one: is there an impairment or disturbance in the functioning of the mind or brain? This could be temporary (like the effects of medication, intoxication, or acute illness) or longer-term (such as dementia, a brain injury, or a learning disability).
Stage two: does that impairment mean the person can’t make this specific decision at this specific time? A person is unable to make a decision if they can’t do one or more of the following:
- Understand the information relevant to the decision
- Retain that information for long enough to make the decision
- Use or weigh that information as part of the decision-making process
- Communicate their decision, by any means — speech, writing, gesture, or assistive technology
If someone can do all four of these for a particular decision, they have capacity for it — even if the decision itself seems unusual or risky to others. It’s genuinely common for a person to have capacity for some decisions and not others, and assessments should be revisited if circumstances change, rather than treated as a permanent label.
Who assesses capacity? In practice, it’s usually whoever needs to make the decision or carry out the relevant act — a doctor for a medical decision, a social worker for a care decision, or a family member for a straightforward day-to-day choice. For significant or contested decisions, involving a professional with relevant expertise (such as a psychiatrist or psychologist) is best practice, and may be required if the matter goes to the Court of Protection.
Planning Ahead: LPAs and Advance Decisions
One of the most practical things the Act enables is planning for a future loss of capacity, before it happens — and this is where a lot of family stress can be avoided with the right paperwork in place early.
Lasting Power of Attorney (LPA). This lets someone (the “donor”) appoint one or more trusted people (the “attorneys”) to make decisions on their behalf if they later lack capacity. There are two separate types, and people often need both:
- A Property and Financial Affairs LPA covers things like bank accounts, bills, and selling a house
- A Health and Welfare LPA covers medical treatment and day-to-day care decisions, and can only be used once the donor has lost capacity for the relevant decision
An LPA must be registered with the Office of the Public Guardian before it can be used, and it’s only valid if it was made while the donor had capacity to understand what they were signing — this is why waiting until after a diagnosis has progressed significantly can make setting one up much harder, or impossible.
Advance Decision to Refuse Treatment (sometimes called a “living will”). This lets someone specify, in advance, medical treatments they do not want to receive in the future if they lose capacity — commonly used around end-of-life care. To be valid and applicable, it must be specific about the treatment being refused and the circumstances, and if it relates to life-sustaining treatment, it must be written, signed, and witnessed.
Without an LPA in place, if someone loses capacity and a decision needs to be made — particularly about finances or significant welfare matters — the only route is often applying to the Court of Protection to be appointed as a deputy, which is slower, more expensive, and more restrictive than acting under a pre-existing LPA.
Deprivation of Liberty Safeguards
For people in care homes or hospitals who lack capacity and whose care arrangements involve a level of supervision and control that amounts to a deprivation of liberty — even where it’s well-intentioned, such as preventing someone with dementia from wandering into danger — the Act requires this to be formally authorised.
This system (currently the Deprivation of Liberty Safeguards, or DoLS, with reforms to a new Liberty Protection Safeguards system having been delayed and under ongoing review as of 2026) exists to make sure restrictions on someone’s freedom are properly scrutinised, proportionate, and regularly reviewed, rather than simply becoming routine practice within a care setting without any independent check.
Families are entitled to be consulted as part of this process and can challenge an authorisation through the Court of Protection if they believe it isn’t in the person’s best interests.
(If you’re dealing with a specific dispute about a care home decision or a family disagreement over best interests, it’s worth reading a more detailed guide on challenging Court of Protection decisions, since the process and timescales differ from a standard capacity assessment.)
Common Misunderstandings Worth Clearing Up
“They have dementia, so they can’t make any decisions.” Not necessarily true, and not how the Act works. Capacity is decision-specific — someone in the early stages of dementia may still have full capacity to decide where they want to live, even if they need support with managing complex finances.
“As next of kin, I automatically have the legal right to make decisions for them.” This is a common and understandable assumption, but it’s incorrect. Being a spouse, adult child, or other close relative gives you no automatic legal authority to make decisions on someone’s behalf — that authority only comes from a registered LPA, a deputyship order, or in the case of medical treatment, being properly consulted as part of a best interests process.
“If I disagree with the decision they’re making, I can just override it.” Only if they genuinely lack capacity for that specific decision. An unwise decision, made by someone with capacity, still has to be respected under the Act’s third principle — even where family members strongly disagree with the choice being made.
Frequently Asked Questions
Can someone with a mental health condition still have capacity to make decisions? Yes. A mental health diagnosis does not automatically mean someone lacks capacity. Capacity depends on whether the specific impairment affects their ability to understand, retain, weigh and communicate a particular decision at that particular time — many people with mental health conditions have full capacity for the vast majority of decisions they make.
What happens if someone loses capacity and hasn’t set up a Lasting Power of Attorney? If there’s no valid LPA in place, decisions about significant matters — particularly finances or major welfare issues — generally require an application to the Court of Protection for a deputyship order. This process is slower and more restrictive than an LPA and typically takes several months, which is why setting up an LPA in advance is strongly recommended wherever possible.
Can family members overrule a person’s own wishes if they think it’s for their own good? Not if the person has capacity for that decision. The Act specifically protects a person’s right to make decisions others consider unwise, provided they understand the decision and its consequences. Family members can only make decisions on someone’s behalf once a proper capacity assessment has established that they genuinely lack capacity for that specific matter.
How often should a capacity assessment be reviewed? There’s no fixed schedule set out in the Act, but assessments are meant to be decision-specific and time-specific, meaning they should be revisited whenever a new decision arises or when circumstances change — such as an improvement or deterioration in someone’s condition, or a change in the type of decision being considered.
Does the Mental Capacity Act apply to under-18s? Generally no — the Act applies to people aged 16 and over, though some of its provisions (such as those relating to research and advance decisions) are limited to those 18 and over. Decisions involving under-16s are typically governed by other legal frameworks around parental responsibility and, where relevant, the Gillick competence test for a child’s own decision-making capacity.
Key Takeaways
The Mental Capacity Act 2005 exists to protect people’s right to make their own decisions wherever possible, while providing a clear, principled framework for when someone genuinely can’t. The five core principles — starting from an assumption of capacity, supporting decision-making, respecting unwise decisions, acting in someone’s best interests, and choosing the least restrictive option — apply to every decision made under the Act, from small everyday choices to major medical and financial matters.
If you’re supporting someone who may lack capacity for a specific decision, the most useful first step is working through the two-stage test properly rather than relying on a diagnosis alone. And if you’re planning ahead for yourself or a family member, setting up a Lasting Power of Attorney while capacity is clearly in place is one of the most practical, low-cost steps you can take to avoid a difficult Court of Protection process later.
