A mental capacity assessment is a crucial part of safeguarding individuals who may struggle to make certain decisions. Whether you’re supporting a loved one or simply trying to understand the law, my guide explains how mental capacity is assessed, who can carry it out, and what happens next—clearly and accurately.
What is a mental capacity assessment?
A mental capacity assessment determines whether a person can make a specific decision at the time it needs to be made.
Under the Mental Capacity Act 2005 (MCA), capacity is always decision-specific and time-specific. This means someone may be able to make everyday decisions—such as what to eat or wear—but lack capacity for more complex matters like managing finances or consenting to medical treatment.
Capacity can also fluctuate, even throughout the day, so timing and context are important.
When is a mental capacity assessment needed?
An assessment may be appropriate if there are concerns about a person’s ability to make decisions due to:
- Dementia or cognitive decline
- Brain injury or stroke
- Mental health conditions
- Learning disabilities
- Confusion, delirium, or sudden behavioural changes
For example, concerns may arise if someone begins making decisions that are:
- Out of character
- Potentially harmful
- Financially risky
- Difficult to understand or explain
It’s crucial to remember that making an unwise decision alone does not mean someone lacks capacity.
How is mental capacity assessed?
The MCA sets out a two-stage test:
Stage 1: Is there an impairment of the mind or brain?
This could be temporary or permanent. Evidence may include:
- Medical diagnoses
- Professional observations
- Changes in behaviour or cognition
Stage 2: Does the impairment mean the person cannot make the decision?
A person is considered unable to make a decision if they cannot:
- Understand relevant information
- Retain that information long enough to decide
- Use or weigh that information as part of decision-making
- Communicate their decision (by any means)
Both stages must be satisfied for a finding of lack of capacity.
For more information, see the Government’s Mental Capacity Act Code of Practice.
Who can carry out a mental capacity assessment?
There is a common misconception that only professionals can assess mental capacity. In reality:
Anyone can carry out a mental capacity assessment, provided they are:
- Involved in the person’s care or decision-making, and
- Responsible for the decision in question
This could include:
- Family members or close friends
- Carers or support workers
- Healthcare professionals (e.g. GPs, nurses)
- Social workers
- Occupational therapists
When is a professional assessment required to carry out a mental capacity assessment?
For significant or complex decisions, such as:
- Selling property
- Making serious medical decisions
- Court proceedings
…it is strongly advisable to involve a qualified professional who can provide a formal, documented assessment.
The five key principles of the Mental Capacity Act
Anyone assessing capacity must follow these five core principles:
- Presume capacity unless proven otherwise
- Support decision-making wherever possible
- Do not treat unwise decisions as incapacity
- Act in best interests if capacity is lacking
- Choose the least restrictive option
These principles are the foundation of lawful and ethical decision-making.
What happens if someone lacks capacity?
If a person is assessed as lacking capacity for a specific decision:
1. A clear record must be kept
This should document:
- The decision in question
- The assessment process
- Evidence supporting the conclusion
This is especially important if matters later involve the Court of Protection.
2. A best interests decision must be made
Any decision made on behalf of the person must:
- Consider their wishes, feelings, beliefs, and values
- Involve relevant others (family, carers, professionals)
- Be the least restrictive option
3. Safeguarding may be required
If there is a risk of harm:
- Local authority safeguarding procedures may apply
- In some cases, action under the Mental Health Act 1983 may be considered
4. Longer-term legal arrangements may be needed
If the lack of capacity is ongoing:
- An application can be made to the Court of Protection to appoint a deputy
- More information is available from the Government’s guidance on becoming a deputy.
What if the person still has capacity but needs support?
If a person has capacity but would benefit from help, they may consider setting up a Lasting power of attorney (LPA).
An LPA allows someone to appoint a trusted person to make decisions on their behalf in the future. Important points:
- The person must have capacity to create an LPA
- They must understand the implications
- It must be registered with the Office of the Public Guardian
You may find this guide helpful: What is a Lasting Power of Attorney? A complete guide for England and Wales
Key takeaways
- Mental capacity is decision-specific and time-specific
- Anyone involved in care can assess capacity—but complexity matters
- The two-stage test must always be followed
- A person should never be assumed to lack capacity
- If capacity is lacking, decisions must be made in best interests
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.
