Testamentary Capacity: Were They Well Enough to Make a Will?

Testamentary capacity is the mental ability the law expects of someone making a will. It is the most common ground for challenging a will in England and Wales, and the most misunderstood. A dementia diagnosis does not by itself make a will invalid. And someone who cannot manage their own bank account may still be perfectly capable of making a will.

What is the legal test?

The test comes from a Victorian case called Banks v Goodfellow (1870), and courts still use it. The person making the will has to:

• Understand that they are making a will and what it will do.
• Have a rough idea of what they own. They do not need to know the value of everything to the penny.
• Be able to think about who has a claim on them. That means the people they might be expected to provide for, whether or not they choose to.
• Be free of any disorder of the mind that twists their feelings towards those people or their sense of what is right.

The fourth point is the one that usually decides dementia and delusion cases. Someone can pass the first three and still fail, because a delusion has turned them against a particular child.

Does the Mental Capacity Act 2005 apply instead?

In practice, no. Courts still use the Banks v Goodfellow test when deciding whether a will that has already been made is valid. In Hughes v Pritchard (2022) the Court of Appeal worked on that basis, though it is worth saying the point was agreed between the parties rather than decided.

The Mental Capacity Act 2005 does have a role. It governs whether the Court of Protection can make a will on someone's behalf. The Law Commission has recommended using a single test, the Mental Capacity Act one, for both questions. That is a recommendation, not law. We cover the wider set of proposals in our article on the biggest shake-up in will law for nearly 200 years.

Who has to prove capacity?

This surprises people. The burden starts with the person putting the will forward, not the person attacking it. But it moves about, in a sequence set out clearly in Key v Key (2010).

• Start: whoever puts the will forward has to show the person had capacity.
• Presumption: if the will was signed properly and looks sensible on its face, the court assumes capacity, and in practice the challenger now has to raise something.
• Back again: if the challenger raises a real doubt, it falls to the person putting the will forward to prove capacity properly.

So a challenger does not have to prove someone lacked capacity outright. They have to raise a genuine, evidenced doubt. That is a lower bar than the one facing someone alleging undue influence.

What evidence do courts look at?

• The file note from the will-drafter. Courts give real weight to the evidence of the solicitor who actually met the person, especially compared with a medical expert giving an opinion years later who never met them.
• Medical records from the time. GP and hospital notes from around the date of the will usually matter far more than what the family remembers.
• The terms of the will itself. A sensible will that makes sense supports capacity. A sudden, unexplained departure from a long-settled plan invites questions.
• What was going on in their life. Grief matters. In Key v Key the will was set aside where the man made it days after his wife of 65 years died. The court accepted that severe grief can cause a disorder that undermines decision-making, even where mild memory problems on their own would not have.

What is the golden rule?

Where an older or seriously unwell person makes a will, the golden rule says a doctor should witness or approve it. They should satisfy themselves the person is capable and understands what they are doing, and write down what they found. It comes from In re Simpson (1977) and is quoted by the Court of Appeal in Sharp v Adam (2006).

Two things to remember. It is good practice for solicitors, not a rule of law, so a will is not invalid because nobody followed it. And following it is no guarantee. In Hughes v Pritchard the Court of Appeal noted that a GP's opinion, backed up by solicitors, can occasionally still turn out to be wrong on other evidence.

What should you do about it?

If you are making a will and age or illness is a factor, see protecting your will from a challenge. If you think a will was made by someone who was not capable, see how to challenge a will. The drafting file and the medical records are where that case is won or lost.

Capacity is often argued alongside knowledge and approval, which asks a narrower question. The overview of legal challenges to wills explains how the grounds compare. For a real capacity dispute, read our write-up of the will that was filmed.

This article is for general information and is not legal advice. If you are worried about a will made by someone who may not have been capable, please get in touch for advice on your own situation.

Sources

• Hughes v Pritchard [2022] EWCA Civ 386 on Find Case Law, The National Archives
• Key v Key [2010] EWHC 408 (Ch) on Find Case Law, The National Archives
• Sharp v Adam [2006] EWCA Civ 449, restating the golden rule from In re Simpson (1977), on Find Case Law, The National Archives
• Modernising wills: final report (16 May 2025), Law Commission