What is Mental Capacity?

To have mental capacity means being able to make your own decisions. We all make decisions, big and small, everyday of our lives and most of us are able to make these decisions for ourselves, although we may seek information, advice or support for the more serious or complex ones.

The law says someone lacking capacity cannot do one or more of the following four things:

  • Understand information given to them
  • Retain that information long enough to be able to make a decision
  • Weigh up the information available to make a decision
  • Communicate their decision.


For large numbers of people their capacity to make certain decisions about their life is affected either on a temporary or on a permanent basis. The Mental Capacity Act covers situations where someone is unable to make a decision because the way their mind or brain works is affected, for instance, by illness or disability, or the effects of drugs or alcohol. A lack of mental capacity could be due to:

  • A stroke or brain injury
  • A mental health problem
  • Dementia
  • A learning disability
  • Confusion, drowsiness or unconsciousness because of an illness or the treatment for it
  • Substance misuse.


In all of these instances the person may lack capacity to make particular decisions at particular times. It does not necessarily mean that they lack capacity to make any decisions at all. A person with a learning disability may lack the capacity to make major decisions, but this does not necessarily mean that they cannot decide what to eat, wear and do each day. A person with mental health problems may be unable to make decisions when they are unwell, but able to make them when they are well.

Many people provide health treatment or social care support to people who may have difficulties making some or all decisions about their lives. If the person is aged over 16 years and living in England or Wales, then the Mental Capacity Act applies to how professionals and other paid carers work with them. Specifically they must follow the guidance set out in the Act's Code of Practice unless there is a good reason for not doing so.