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A will is invalid for lack of testamentary capacity if, when it was made, the person could not understand what a will does, what they owned, or whose claims they ought to consider, or if a disorder of the mind distorted their choices. That is the test from Banks v Goodfellow (1870), still applied by the courts. A properly signed will that looks rational is presumed valid until someone raises a real doubt. A diagnosis of dementia is evidence, not an answer. The court looks at the person's capacity when the will was made, using medical records, the will-writer's notes and the accounts of people who knew them.
When someone you loved made a will late in life, perhaps while unwell or confused, it is natural to wonder whether they really understood what they were signing. "Testamentary capacity" is the legal name for the mental ability needed to make a valid will. This page explains how the courts decide whether someone had it, who has to prove what, and the kinds of evidence these cases turn on.
This describes the law of England and Wales. Scotland and Northern Ireland have their own rules and courts for disputes about wills.
Lack of capacity is one of several grounds on which a will can be challenged. For the others, and for how a challenge runs from start to finish, see our guide to contesting a will.
The test comes from an 1870 case, Banks v Goodfellow. It is not in any Act of Parliament, and the courts still apply it. In Hughes v Pritchard [2022] the Court of Appeal said the test for testamentary capacity "remains that set out in Banks v Goodfellow", and quoted Chief Justice Cockburn's words: a testator (the person making the will)
"shall understand the nature of the act and its effects; shall understand the extent of the property of which he is disposing; shall be able to comprehend and appreciate the claims to which he ought to give effect; and, with a view to the latter object, that no disorder of the mind shall poison his affections, pervert his sense of right, or prevent the exercise of his natural faculties"
The full passage, as quoted in Clitheroe v Bond [2021], goes on: "that no insane delusion shall influence his will in disposing of his property and bring about a disposal of it which, if the mind had been sound, would not have been made."
In plainer terms, when the will was made the person needed to:
The test is about what the person was able to understand, not what they happened to remember. In Hughes v Pritchard the Court of Appeal adopted the words "capacity is concerned with the potential to understand. It is not a test of memory", and said a will-maker does not need to recall the terms of an earlier will "as long as they are capable of accessing the information, if needed, and of understanding it once reminded of it."
A diagnosis of dementia or another illness affecting the mind is important evidence, but it does not by itself make a will invalid. The question is the person's capacity when the will was made. In Hughes v Pritchard the will-maker had dementia, and a cognitive test carried out before he made his will had indicated "a moderately severe degree of mental impairment". The trial judge found he lacked capacity; the Court of Appeal disagreed and upheld the will.
The Mental Capacity Act 2005 has its own test. Under section 3, a person is unable to make a decision if they cannot understand the relevant information, retain it, use or weigh it, or communicate their decision. That test governs decisions made by and for people who are alive — care, treatment, attorneys, deputies. The Court of Protection can also make a will for a living person who lacks capacity under section 18 of the Act (see our guide to statutory wills).
Whether that statutory test also applies when a court looks back at a will made by someone who has since died was argued in Clitheroe v Bond [2021]. Mrs Justice Falk held that it does not: "The Banks test ... has not been swept away by the MCA." Her reasons included that the Act's definition of capacity is stated to apply "for the purposes of this Act", and that its purpose is decision-making for people who lack capacity now, not deciding afterwards whether a completed act was valid. The High Court has followed that since, most recently in Ugolor v Ugolor [2026].
The Court of Appeal has not decided the point after hearing argument on it. In Hughes v Pritchard it applied Banks v Goodfellow but recorded that no one had argued the test did not survive the 2005 Act. So the current position is the High Court's, consistently applied.
The burden of proof in capacity cases moves between the two sides. Clitheroe v Bond sets it out:
The standard of proof is the ordinary civil one: the balance of probabilities, meaning more likely than not.
Capacity is a separate question from whether the will-maker knew and approved what the will said, and from whether they were pressured into it. Challenges often raise more than one ground. See undue influence and our guide to contesting a will.
Where a solicitor is asked to prepare a will for someone elderly or seriously ill, the so-called golden rule is that they should arrange for a doctor to assess the person's capacity and understanding first, and to make a written record at the time. It comes from two 1970s cases decided by Templeman J, Kenward v Adams (1975) and Re Simpson (1977), as summarised in Key v Key [2010].
The courts have been clear about its limits:
So a will is not invalid just because no doctor saw the person, and it is not safe from challenge just because one did. In Hughes v Pritchard the Court of Appeal said that where a will is rational on its face, the view of an independent lawyer who was aware of the surrounding circumstances is "likely to be of considerable importance", though the judge still has to weigh all the evidence.
Because the person who made the will has died, capacity has to be judged from what was recorded and observed at the time. The evidence usually includes:
No official body publishes how often capacity challenges succeed, or what an expert report costs, and this page does not estimate either.
A capacity challenge is a "probate claim" under Part 57 of the Civil Procedure Rules. Rule 57.7(4) requires anyone who says the will-maker lacked testamentary capacity to "set out the contention specifically and give particulars of the facts and matters relied on". A bare assertion is not enough.
Rule 57.7(5) also allows a defendant not to put forward a positive case but to insist that the will be "proved in solemn form" — formally proved in court, with the attesting witnesses cross-examined. A defendant who does that will not be ordered to pay costs unless the court considers "there was no reasonable ground for opposing the will".
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