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Wills & Capacity

Testamentary Capacity: Mental Capacity to Make a Will

Testamentary capacity is the mental ability the law requires to make a valid will. In England and Wales it is measured by the long-standing Banks v Goodfellow test.

8 min read · Written by the Fairchild Oldfield team · Last reviewed: July 2026

4 tests
The Banks v Goodfellow standard asks whether a person understood the act of making a will, the extent of their property, the claims they ought to consider, and was free of any disorder of mind affecting those decisions.
Based on gov.uk, HMRC IHT Manual IHTM12045, as at July 2026, subject to change.

Testamentary capacity is the level of mental capacity a person needs to make a valid will. In England and Wales the legal starting point is the common-law test set out in the 1870 case Banks v Goodfellow, which gov.uk still cites as the standard for whether someone had a "sound disposing mind" when they made their will (gov.uk, HMRC IHT Manual, as at July 2026, subject to change).

Capacity is one of the requirements for a valid will, alongside being 18 or over, acting voluntarily, and signing in front of two witnesses (gov.uk, make sure your will is legal, as at July 2026, subject to change). Where capacity is in doubt, a will can be challenged after death. This guide explains the test, how capacity is assessed, and where it fits within a wider estate planning guide. Figures and rules are current as at July 2026 and are subject to change.

What is testamentary capacity?

Testamentary capacity is the mental ability the law requires for a person to make a valid will. It means the will-maker, called the testator, understood what they were doing when they gave instructions and signed. Capacity is decision-specific: a person may have capacity to make a will even if they need help with other matters, and a medical diagnosis alone does not decide the question (gov.uk, HMRC IHT Manual, as at July 2026, subject to change).

The Banks v Goodfellow test

The Banks v Goodfellow test is the common-law standard for testamentary capacity in England and Wales, requiring a "sound disposing mind". In broad terms the testator must understand that they are making a will and its effect, understand the extent of the property being left, appreciate the claims of those they might be expected to provide for, and not be affected by any disorder of mind that distorts those judgements (gov.uk, HMRC IHT Manual, as at July 2026, subject to change).

Element of the testWhat the testator must do
Nature of the actUnderstand that they are making a will and that it takes effect on death
Extent of propertyHave a general recollection of the property being disposed of
Claims on the estateUnderstand the nature and extent of the claims of those they might provide for
No disorder of mindNot be subject to any disorder of mind that perverts their sense of right or judgement

Source: gov.uk, HMRC IHT Manual IHTM12045, drawing on Banks v Goodfellow (1870), as at July 2026, subject to change.

What does "sound mind" mean for a will?

Being of "sound mind" for a will means understanding the act itself, not passing a general mental health test. gov.uk lists "be of sound mind" as a validity requirement alongside acting voluntarily and being free from pressure (gov.uk, as at July 2026, subject to change). A person can have conditions such as early dementia and still meet the standard if, at the moment of making the will, they understood what they were doing.

The statutory backdrop

The Mental Capacity Act 2005

The Mental Capacity Act 2005 sets a general, decision-specific framework for capacity in England and Wales, starting from a presumption that an adult has capacity unless shown otherwise (legislation.gov.uk, Mental Capacity Act 2005, as at July 2026, subject to change). For wills, the courts have generally continued to apply the older Banks v Goodfellow test, so the two sit alongside each other rather than one replacing the other.

The Act also lets the Court of Protection make a "statutory will" for someone who lacks the capacity to make one themselves, subject to safeguards (legislation.gov.uk, Mental Capacity Act 2005 s.18, as at July 2026, subject to change). Which standard applies can depend on whether the person is making their own will or the court is acting for them.

Sources: legislation.gov.uk and gov.uk, HMRC IHT Manual, as at July 2026, subject to change.

The starting point

Presumed capable

The Mental Capacity Act 2005 begins from the presumption that an adult has capacity to make a decision unless the contrary is established, and that a decision is not unwise merely because others disagree with it (legislation.gov.uk, s.1, as at July 2026, subject to change).

How is testamentary capacity assessed?

Capacity is judged at the time the will is made, by reference to the Banks v Goodfellow elements rather than a diagnosis. Where there is any doubt, a common practice is the "golden rule", under which a will for an elderly or unwell person is witnessed or assessed by a medical practitioner who records their view. This is guidance rather than a strict legal requirement, but it can make a later challenge harder to sustain (gov.uk, HMRC IHT Manual, as at July 2026, subject to change).

  1. Timing. Capacity is tested at the point of giving instructions and executing the will, not months later.
  2. The four elements. Each limb of the Banks v Goodfellow test is considered on the facts.
  3. Contemporaneous evidence. File notes, a capacity assessment and the will-maker's own words carry weight.
  4. Medical input. Where capacity is in question, a practitioner's assessment can be recorded at the time.
A worked example (illustration only). Mr A, aged 82 and in the early stages of dementia, wants to update his will to leave his home to his daughter. On a good day he clearly understands he is making a will, knows he owns the house and some savings, and can explain why he is providing for his daughter and not his estranged son. Following the golden-rule practice, his GP assesses and records that he meets the Banks v Goodfellow elements at that time (gov.uk, HMRC IHT Manual, as at July 2026, subject to change). Even with a diagnosis, the will may be valid because capacity is decision-specific. Every situation differs, so this is general information rather than advice about any real person.

Can a will be challenged for lack of capacity?

Yes. Lack of testamentary capacity is one of the main grounds on which a will can be disputed after death, and it sits among the reasons a will may be set aside (gov.uk, HMRC IHT Manual, as at July 2026, subject to change). If a will is found invalid, an earlier valid will may take effect, or the intestacy rules may apply (gov.uk, intestacy rules, as at July 2026, subject to change). For the wider picture, see our notes on contesting a will and on what makes a will invalid.

Where capacity is lacking

Statutory wills through the Court of Protection

I

Capacity in doubt

A person lacks the capacity to make or change their own will.

II

Application

Someone applies to the Court of Protection for a statutory will on their behalf.

III

Best interests

The court decides in the person's best interests under the Act. legislation.gov.uk, s.18, as at July 2026, subject to change.

IV

Approved will

If approved, the statutory will is executed under the court's direction.

Testamentary capacity in Scotland and Northern Ireland

This guide describes the law of England and Wales, where the Banks v Goodfellow test and the Mental Capacity Act 2005 apply. Northern Ireland follows a broadly similar approach to capacity and will formalities. Scotland has its own succession law and a different framework for adults with incapacity, and it allows those aged 12 or over to make a will (gov.uk, HMRC IHT Manual, as at July 2026, subject to change). Where an estate touches more than one UK nation, it can be worth taking advice in each. Testamentary capacity also matters for later inheritance tax, since a valid will can direct assets to a spouse or civil partner tax free and toward the available thresholds (gov.uk, as at July 2026, subject to change).

Frequently asked questions

What is testamentary capacity?

Testamentary capacity is the mental capacity the law requires to make a valid will. In England and Wales it is measured by the Banks v Goodfellow test: understanding the act of making a will, the extent of the property, and the claims of those who might expect to benefit, free of any disorder of mind affecting those judgements (gov.uk, as at July 2026, subject to change).

Can someone with dementia make a valid will?

Potentially, yes. A diagnosis such as dementia does not automatically remove testamentary capacity, because capacity is decision-specific and judged at the moment the will is made (gov.uk, as at July 2026, subject to change). Where there is any doubt, many people choose to have a capacity assessment recorded at the time, which can help support the will later.

Who decides if a will-maker had capacity?

At the time, the person preparing the will forms a view, and where doubt exists a medical practitioner may assess and record capacity under the golden-rule practice. After death, if a will is disputed, a court decides whether the Banks v Goodfellow test was met on the evidence (gov.uk, as at July 2026, subject to change). It can be worth discussing this with a qualified professional.

What happens if a will is found invalid for lack of capacity?

If a will is set aside for lack of capacity, any earlier valid will may take effect instead. Where there is no valid earlier will, the intestacy rules decide who inherits, and unmarried partners receive nothing under those rules (gov.uk, intestacy rules, as at July 2026, subject to change). The outcome depends on the facts of each estate.

Is the Mental Capacity Act the same as the Banks v Goodfellow test?

Not quite. The Mental Capacity Act 2005 sets a general, decision-specific framework and presumes capacity unless shown otherwise (legislation.gov.uk, as at July 2026, subject to change). For wills, the courts have generally continued to apply the older Banks v Goodfellow test, so the two operate alongside each other rather than one simply replacing the other.

Can a will be made for someone who lacks capacity?

In limited circumstances, yes. The Court of Protection can authorise a "statutory will" for a person who lacks capacity to make one, deciding in their best interests under the Mental Capacity Act 2005 (legislation.gov.uk, s.18, as at July 2026, subject to change). This involves a court application, so many people take advice from a qualified professional before starting.

About Fairchild Oldfield

The Fairchild Oldfield team brings together estate planning, tax, independent financial advice and client care, working with families across England and Wales.

Fairchild Oldfield are estate planning specialists and will writers, not a firm of solicitors. This article is general information based on practical experience, not legal, tax or financial advice.

Important: This article is general information only and is not legal, tax or financial advice. Reading it does not create a professional relationship. It is based on the law of England and Wales, and other UK jurisdictions may differ. Figures and rules are current as at July 2026 and are subject to change. Before acting, many people choose to seek advice from a suitably qualified professional, such as a solicitor, a STEP practitioner, an accountant, or an FCA-authorised financial adviser, who can consider your individual circumstances.

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