Mental Capacity vs Testamentary Capacity What’s the Difference?

Although the terms mental capacity and testamentary capacity sound similar and are often used interchangeably, they refer to different legal tests and types of decisions. 

Questions about capacity are becoming increasingly common in private client practice, particularly when advising older clients, those living with Dementia, or individuals experiencing mental health difficulties. Below, I explain the differences between the terms and why they are important. 

What is mental capacity?

Mental capacity is governed by the Mental Capacity Act 2005, and it applies to decisions made during a person’s lifetime, such as managing finances, buying or selling property, making Lasting Powers of Attorney or decisions about healthcare and treatment.

Under the Act, a person must be able to understand, retain, use or weigh relevant information and communicate their decision. Put simply, someone maybe able to make some decisions, but not others, and their capacity may change over time.

What is testamentary capacity?

Testamentary capacity is the legal and mental ability of a person to make a valid will. It refers to the level of understanding and judgements required for an individual to make decisions about how their estate should be distributed after their death. 

Does a diagnosis of a mental health condition mean someone cannot make a will?

A diagnosis of Dementia, Alzheimer’s disease, depression or another mental health condition does not automatically prevent someone from making a valid will. Many people with these conditions still have testamentary capacity. They key question is whether they understand the nature and effect of the will at the time it is made (Banks v Goodfellow [1870]).

The law also recognises that capacity can fluctuate. Someone may have periods of confusion but still be capable of making a valid will during a clearer period. 

Could the law change?

Over the years, the courts have considered many disputes concerning testamentary capacity. In Key v Key [2010], the court recognised that factors such as grief, confusion and delusions can impair a person’s ability to understand and evaluate the decisions made in a will. Conversely, in Walker v Badmin [2014], the court confirmed that a diagnosis of mental illness or cognitive impairment does not automatically mean that a person lacks testamentary capacity, provided they retain sufficient understanding of the nature and effect of their decisions. Although the Law Commission has recommended replacing the common law test in Banks v Goodfellow with the statutory test under the Mental Capacity Act 2005, the law remains unchanged. Most recently, in Leonard v Leonard [2024], the High Court reaffirmed that testamentary capacity continues to be assessed under Banks v Goodfellow, with the Mental Capacity Act serving as a useful cross-check rather than the governing legal test. Together, these cases illustrate the courts’ consistent focus on a testator’s actual understanding and decision-making ability at the time the will is made, rather than on the mere presence of illness, impairment or vulnerability

The importance of getting it right

Capacity concerns should never be ignored, but they should never be assumed either.

Just because someone is elderly or has been diagnosed with Dementia does not mean they cannot make a valid will. Equally, where there are genuine concerns, it is important to take appropriate steps to ensure capacity is properly considered and documented.

Where there are any doubts, solicitors should consider following the well-known Golder Rule, which recommends obtaining a medical opinion on capacity where the testator is elderly or seriously ill. Although it is not a legal requirement, it can provide valuable evidence if the will is later challenged. 

If you would like to discuss making or updating a will where there may be concerns about capacity, please get in touch with Diana Popescu at dpopescu@se-solicitors.co.uk