Assessing Mental Capacity

There are various mental illnesses that affect mental capacity, from dementia and psychosis (i.e. schizophrenia) to alcohol and drug dependence. However, simply because a person has a diagnosis of a mental illness does not mean that they lack the requisite capacity to make a Will. Likewise, simply because someone does not have a diagnosis, does not mean that they have it.


In the National Mental Capacity Forum Chair’s Annual Report 2016 it was estimated that approximately 2 million people in the UK do not have mental capacity. The most common reason for this is mental illness.

Dementia is one of the most common forms of mental illness and is very common in the UK as the following statistics from Alzheimer’s Research UK shows:-

  • A person’s risk of developing Dementia over the age of 65 is one in 14.
  • A person’s risk of developing Dementia over the age of 85 is one in 6.
  • Globally, the number of people living with Dementia will increase by 204% by 2050.

More notably, whilst around 944,000 in the UK are estimated to be living with Dementia, only 525,000 have received a formal diagnosis. Therefore, over a third of people living with Dementia are not, and may never be, diagnosed. On average it can take 2 – 3 years before a person is diagnosed with Dementia after symptoms begin.

Relative to Will making, the above statistics show that it may become increasingly likely that signs of Dementia, for example, may not be immediately apparent to a person instructed to make a Will on behalf of someone, if no diagnosis is present to initially raise any doubts regarding capacity.

A person diagnosed, and living with, a mental illness such as Dementia can have the requisite capacity to make a Will. Capacity may be unimpaired in the early stages of Dementia. For example, they may have a lucid interval of capacity or their capacity may improve after treatment. However, more often, Dementia will affect a person’s capacity to make a Will.

Testamentary Capacity

The requisite capacity to make a Will is known as testamentary capacity. The test is set out by case law dating back to 1870. The person making the Will must:

  • Understand the nature of making a will and its effects – This requires long term memory and judgement.
  • Understand the extent of the property of which they are disposing – This requires more recent knowledge and autobiographical memory.
  • Be able to comprehend and appreciate the claims to which they ought to give effect – This requires an up-to-date autobiographical memory and executive function to enable judgements about potential claims. It further requires a working memory to hold this information in mind.
  • Have no disorder of the mind that perverts their sense of right or prevents the exercise of their natural faculties in disposing of their property by will.

At the time of making a Will, a formal assessment of capacity to determine the same can be undertaken by a medical professional who is a specialist in this area where there are any doubts. However, as it is only an advisory step, such an assessment is not always undertaken, especially if there are no warning signs picked up on. In the case of personally made Wills, it is even more uncommon that a person would arrange their own assessment.

Post Death

If no assessment is undertaken at the time of making the Will, then the question arguably always remains as to whether a person had testamentary capacity.

Obtaining a person’s medical records is a common step undertaken by a Contentious Probate Lawyer when there is a dispute as to the validity of a Will. Simple perusal of the records can give rise to evidence to strengthen a claim that a person lacked testamentary capacity, but equally the contents can be misleading.

For example, a person’s cognition (the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses) is regularly tested by doctors at varying levels where someone may be experiencing problems with memory. Scores in response to various levels of tests testing cognition, may be present in a person’s medical records where capacity is a concern. However, in a study previously conducted on behalf of the Alzheimer’s Society, it was determined that cognition testing alone is insufficient to assess the presence of capacity.

If there are any concerns as to a person’s testamentary capacity following changes in a Will coming to light on a person’s death, then a retrospective assessment of capacity is something that can be undertaken.

A retrospective assessment involves a specialist reviewing GP notes, hospital notes, care home records, Solicitors records etc. to undertake a meticulous analysis of medical and psychiatric issues to assess any impact on a person’s testamentary capacity.


If you have been cut out of a Will as a result of a significant change by a relative or someone close, there may be an underlying mental illness affecting their testamentary capacity at the time of making the Will.

If you have learnt that a relative or person close to you has cut you out of their Will for unexplained reasons, it would be advisable to take advice from one of our specialist Lawyers in our Contentious Trusts and Probate team.