GUIDES
The Mental Capacity Act 2005 requires a presumption of capacity, practicable support and respect for unwise choices. Where a person lacks capacity for the particular decision, acts and decisions under the Act must follow best interests and consider less restrictive ways to achieve the purpose.
Author: Nellie Supports Ltd
Publication Date: 15/05/2026
39 Essex Chambers, Mental Capacity Guidance Note: Carrying out and recording capacity assessments.
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The Mental Capacity Act 2005 requires a presumption of capacity, practicable support and respect for unwise choices. Where a person lacks capacity for the particular decision, acts and decisions under the Act must follow best interests and consider less restrictive ways to achieve the purpose. This guide covers the relevant evidence, support, process and limits in England and Wales.
The Mental Capacity Act 2005 requires a presumption of capacity, practicable support and respect for unwise choices. Where a person lacks capacity for the particular decision, acts and decisions under the Act must follow best interests and consider less restrictive ways to achieve the purpose. The framework generally concerns people aged 16 and over in England and Wales, with specific age limits and exceptions. Wills and some other decisions have distinct legal rules.
Section 1 of the Mental Capacity Act 2005 sets out five principles that govern all decisions made under it. They are the presumption of capacity, the duty to support decision-making, the right to make unwise decisions, the best interests duty, and the least restrictive principle. Every assessment and decision must be read through these principles.
A person must be assumed to have capacity unless it is established that they lack it. The burden is on the person asserting incapacity, and the standard is the balance of probabilities. This means capacity is the starting point, and an assessment exists to test that presumption, not to confirm an assumption that someone cannot decide.
A person is not to be treated as unable to make a decision unless all practicable steps to help them have been taken without success. This includes giving information in an accessible way, choosing the right time and place, using communication aids, and involving people who can help. Support must come before any conclusion about capacity.
A person is not to be treated as lacking capacity merely because they make a decision others consider unwise. Capacitous adults are entitled to make choices that seem eccentric, risky or wrong to others. The assessment must distinguish a genuinely unwise but capacitous decision from an inability to use or weigh the relevant information.
Any act or decision taken for someone who lacks capacity must be in their best interests. This is a structured process under section 4, taking account of the person's past and present wishes, feelings, beliefs and values, and the views of those close to them. Best interests is not simply what others think is best for the person.
Before acting or deciding under the Act for a person who lacks capacity, consider whether the purpose can be achieved as effectively in a way that restricts their rights and freedom less. This is part of the overall lawful, best-interests decision and does not authorise an otherwise unavailable or unlawful option.
The principles are not a menu to choose from. A decision must presume capacity, offer support, respect unwise choices, and, only where capacity is genuinely lacking, move to a best interests decision taken in the least restrictive way. Skipping any step, particularly the duty to support, undermines the lawfulness of what follows.
A capacity assessment that ignores the principles is open to challenge. Failing to provide support, treating an unwise decision as proof of incapacity, or moving to best interests without establishing a lack of capacity are all errors that the principles are designed to prevent. A sound assessment shows the principles being applied.
The five principles protect autonomy while providing a lawful route to act for those who genuinely cannot decide. They require capacity to be presumed, decision-making to be supported, unwise choices to be respected, and any intervention to be in the person's best interests and as unrestrictive as possible.
Presume capacity, offer all practicable decision-making support and do not equate an unwise choice with incapacity. Where capacity is lacking, acts and decisions under the Act must serve best interests and consider whether the purpose can be achieved as effectively with less restriction.
Most of the Act’s decision-making framework concerns people aged 16 and over, with specific statutory exceptions. Making an LPA requires the donor to be 18 or over; advance decisions to refuse treatment have their own adult requirements. Capacity to make a will is governed by separate common-law principles, not simply by an MCA age rule.
Capacity asks whether the person can make this decision with practicable support. Only where they cannot does the relevant MCA best-interests process permit someone with lawful authority or protection to act. In an emergency, the principles still apply; the lawfulness of urgent action depends on its circumstances and applicable powers, with the basis and reasoning recorded.
The related guides below provide further explanation of the decisions, evidence and legal processes discussed here.
Name the decision and give the person practicable support before assessing capacity. If it is established that they cannot decide, identify who has lawful authority and apply section 4 rather than treating family agreement as permission to act.
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