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Testamentary Capacity: Proving You're 'Of Sound Mind' in the UK

· 12 min

Margaret, 78, wanted to update her will after her husband died. She had early-stage Parkinson's and occasional memory lapses. Her daughter worried that creating a new will might be challenged by Margaret's son, who would inherit less under the new arrangement.

Margaret's GP confirmed she understood exactly what she was doing. She could explain her assets—£340,000 house, £85,000 savings—identify her family members, and articulate why she wanted to leave more to her daughter who had been her primary carer. Despite her Parkinson's diagnosis, Margaret had full testamentary capacity.

Thousands of older people in the UK delay or avoid making wills because they fear their mental capacity might be questioned. With 982,000 people living with dementia in the UK—projected to reach 1.4 million by 2040—understanding testamentary capacity has never been more important.

This article explains exactly what "of sound mind" means in UK law, when you need medical proof of capacity, and how to protect your will from future challenges.

Table of Contents

What Is Testamentary Capacity?

Testamentary capacity is the legal and mental ability to make a valid will. When you see "of sound mind" in legal documents, it's the traditional phrase describing this capacity.

Critically, testamentary capacity is assessed at the specific time you make your will, not as a general state. You might struggle with day-to-day decisions but still have full capacity to create a valid will. The threshold is deliberately low to allow elderly people to make wills in their declining years.

Testamentary capacity is completely separate from the Mental Capacity Act 2005, which governs other decisions. This distinction matters enormously in practice.

Approximately 60% of capacity challenges involve elderly testators with dementia or cognitive decline. But dementia doesn't automatically mean you lack capacity.

John, 82, has mild dementia and can't manage his finances day-to-day. He forgets appointments and struggles with his bank statements. Yet John can still make a valid will because he understands what a will does, knows he has about £180,000 in assets, and clearly wants his two daughters to inherit equally.

Contrast this with Helen, 68, who has advanced dementia. She can't name her children consistently or remember she owns her house. Helen lacks testamentary capacity.

The difference? Understanding what you're doing at the moment you make your will, not perfect mental health across all areas of life.

Every testamentary capacity assessment in the UK uses the same legal test, established in the 1870 case Banks v Goodfellow (1870) LR 5 QB 549.

Despite the Mental Capacity Act 2005, courts confirmed in Walker v Badmin (2015) that Banks v Goodfellow is "the correct and only test" for wills. This Victorian-era standard has stood the test of time because it strikes the right balance—protective but not paternalistic.

You must satisfy all four requirements to have testamentary capacity.

First: Understand the nature of making a will and its effects.

Sarah, 85, must understand that a will is a legal document stating who gets her property when she dies, and that she can change it while alive. She doesn't need to understand complex tax implications or legal terminology—just the basic concept.

Second: Understand the extent of the property you're disposing.

David, 76, needs to know roughly what he owns. "My house worth about £300,000, savings of £50,000, my car" is sufficient. He doesn't need exact valuations or detailed asset lists—a general understanding works.

Third: Comprehend and appreciate the claims to which you ought to give effect.

Emma, 70, must identify who might reasonably expect to inherit—spouse, children, dependents—even if she chooses to exclude some. She doesn't have to leave them anything, just understand they exist and have potential claims.

This requirement protects against tragic situations where someone genuinely forgets they have children or doesn't understand family relationships.

Fourth: Have no disorder of the mind that perverts your sense of right or prevents exercising natural faculties.

This limb targets delusional thinking that warps judgment. James has paranoid delusions that his daughter is "poisoning" him without any evidence. If he excludes her based purely on this unfounded delusion, the will fails the test.

Contrast this with rational decisions others might disagree with. If James excludes his daughter because she hasn't contacted him in 10 years, that's fine—it's his choice based on facts, not delusion.

The threshold for each requirement is relatively low. You don't need perfect understanding—just sufficient comprehension of what you're doing. This accessibility means most people easily meet the standard, even with age-related cognitive changes.

Recent case law, including Leonard v Leonard (2024), confirmed that Banks v Goodfellow has "stood the test of time" and remains the definitive standard.

Testamentary Capacity vs. the Mental Capacity Act 2005

These are two separate legal tests that serve different purposes.

Banks v Goodfellow applies only to wills and hasn't been replaced by the Mental Capacity Act 2005. The MCA 2005 governs decisions by living persons about finances, healthcare, and welfare. Walker v Badmin (2015) definitively confirmed this separation.

The key difference is the threshold. Testamentary capacity has a lower bar than MCA 2005 capacity. Someone might lack capacity to manage day-to-day finances under the MCA but still have full testamentary capacity.

Here's how they compare:

Aspect Testamentary Capacity Mental Capacity Act 2005
Applies to Wills only Living decisions (finances, healthcare)
Legal test Banks v Goodfellow (1870) MCA 2005, Sections 2-3
Threshold Lower Higher
Understanding required Immediate effect of will All reasonably foreseeable consequences
Can fluctuate Yes—assessed at moment of signing Yes—time and decision specific
Who assesses Medical professional or court retrospectively Court of Protection or assessor for living person

Robert, 79, lacks capacity under the MCA 2005 to manage his finances. He can't understand bank statements or make investment decisions. His daughter holds a Lasting Power of Attorney for his financial affairs.

Yet Robert can make a valid will. He understands what a will does, knows he has about £200,000 in total assets, and clearly identifies his two children as the people who should inherit equally.

This matters enormously in practice. Don't assume that because someone has lost capacity for day-to-day financial decisions, they can't make a will. The tests are different, and the will-making threshold is deliberately more accessible.

When Do You Need a Medical Assessment? The "Golden Rule"

The "golden rule" from Kenward v Adams (1975) isn't a legal requirement but represents best practice when capacity might be questioned.

The full quote states: "In the case of an aged testator or a testator who has suffered a serious illness, there is one golden rule which should always be observed... the making of a will ought to be witnessed or approved by a medical practitioner who satisfies himself of the capacity and understanding of the testator, and records and preserves his examination and finding."

When does the golden rule apply? It's recommended for elderly testators (typically 80+), anyone with serious illness, diagnosed dementia or cognitive impairment, previous mental health issues, or anyone taking medication affecting cognition.

What happens during a golden rule assessment? A GP or specialist assesses capacity using the Banks v Goodfellow test, interviews the testator about their assets and intentions, and records findings in a written report.

The cost ranges from £500+ for basic assessments according to private GP services, with more complex cases potentially costing significantly more. Some NHS GPs may provide this service, though availability varies.

Timing is critical. Recent case law held that five weeks between instructing a GP and receiving a report was too long. Solicitors should follow up after 10 days to ensure the assessment happens close to will signing.

Patricia, 84, has no diagnosed conditions but her children worry about "senior moments." The golden rule applies due to age. Michael, 72, had a stroke three months ago affecting speech but not comprehension. The golden rule applies due to serious illness.

Susan, 68, has early-stage Alzheimer's. The golden rule definitely applies. Tom, 45, has no health issues. The golden rule doesn't apply.

The assessment involves reviewing medical and psychiatric history, conducting a mental state examination, performing cognitive testing for memory and understanding, asking specific questions about the will, and producing a written report with an opinion on capacity.

Following the golden rule doesn't guarantee your will won't be challenged. But it provides powerful evidence if a challenge occurs, potentially saving tens of thousands in litigation costs.

The Presumption of Capacity and Burden of Proof

A properly executed will that appears rational is presumed to be made with capacity. This presumption is strong, and challengers face a high burden of proof.

The three-stage burden of proof established in Key v Key (2010) works like this:

First, the person defending the will must show it was properly executed and appears rational on its face. If so, the presumption of capacity applies automatically.

Second, the burden shifts to the challenger to raise "real doubt" about capacity. They need medical evidence of cognitive impairment, witness testimony of confusion, or irrational provisions requiring explanation.

Third, if real doubt is established, the burden shifts back to the defender to prove capacity existed on the balance of probabilities—meaning more likely than not.

Here's how this plays out in practice. An executor produces a properly signed will leaving the estate to two children equally. The presumption of capacity applies.

An excluded sibling provides GP records showing advanced dementia diagnosis two months before the will was signed. This raises real doubt.

Now the executor must produce evidence of capacity—ideally a golden rule medical assessment, or detailed solicitor attendance notes, or witness evidence of lucidity at the relevant time.

The standard of proof throughout is balance of probabilities, not beyond reasonable doubt. But the presumption of capacity is deliberately strong.

While approximately 10,000 people dispute wills annually in England and Wales, only around 195 disputes resulted in court proceedings in 2021-22. Most settle, and the success rate for overturning wills on capacity grounds is believed to be low.

The law protects validly executed wills. Challengers need substantial evidence, not just suspicion or disagreement with the will's terms.

Special Rules: Lucid Intervals and the Parker v Felgate Rule

Two important legal principles can validate wills even when capacity concerns exist.

Lucid intervals are periods of mental clarity in someone whose capacity otherwise fluctuates. A will made during a lucid interval can be valid even if the person lacks capacity before and after.

This most commonly applies with dementia patients, people with severe depression, or those with delirium from infection or medication.

Those defending the will must prove the lucid interval existed at the exact time of execution. This is why timing of medical assessment matters—it must assess capacity at the moment of giving instructions and signing.

Dorothy, 81, has vascular dementia with good days and bad days. On Monday, she's confused and can't remember her grandson's name. On Wednesday, she's clear-headed, discusses her will with her solicitor, and explains her assets and beneficiaries coherently. On Friday, she's confused again.

The will made Wednesday during the lucid interval is valid if medical evidence confirms her clarity at that specific time.

The Parker v Felgate rule from Parker v Felgate (1883) 8 PD 171 provides another exception. A will can be valid even if the testator lacks capacity at execution, provided:

  • They had capacity when giving instructions to the solicitor
  • The will was prepared according to those instructions
  • At execution, they understood they were signing a will made per their earlier instructions

The original case involved Georgina Compton, who gave clear will instructions while well but fell into a coma from Bright's disease before signing. She was roused enough to execute the will, understanding she was signing the document her solicitor had prepared per her instructions. The will was held valid.

This rule applies most commonly when testators give clear instructions while competent, then deteriorate before signing due to stroke, rapid dementia progression, or terminal illness.

A solicitor takes detailed instructions from a client with clear capacity. The client has a stroke before the will can be executed. The client can't fully discuss will terms but understands "this is the will I asked you to prepare." The will can be valid under Parker v Felgate.

The rule remains good law, endorsed by the Court of Appeal, though practitioners sometimes feel uneasy that someone "lacking capacity" can execute a will.

Common Misconceptions About Testamentary Capacity

Several myths prevent people from making wills when they could do so perfectly legally.

Misconception: "A dementia diagnosis means you can't make a will."

Truth: Dementia is a spectrum. Early-stage dementia often doesn't affect testamentary capacity. With 982,000 people in the UK having dementia, many retain testamentary capacity throughout most of their illness.

Arthur has early Alzheimer's. He forgets appointments and recent conversations, but clearly understands he wants his £250,000 estate split equally between his three children. He has capacity.

Misconception: "You need to understand tax implications and legal terminology."

Truth: You only need to understand the effect of your will in plain English, not legal or tax technicalities. You don't need to understand "nil-rate band" or "residuary estate"—just "my daughter gets my house, my son gets my savings."

Misconception: "Being old, eccentric, or making unusual decisions means you lack capacity."

Truth: You can have full capacity and make choices others think are odd, unfair, or unwise. Courts don't judge the rightness of decisions, only whether you understood what you were deciding.

Edward, 88, leaves nothing to his children and everything to his cat sanctuary. Unusual, but valid if he understood his decision and the Banks v Goodfellow test is satisfied.

Misconception: "Physical disability or illness affects mental capacity."

Truth: Physical and mental capacity are separate. Paralysis, blindness, deafness, or terminal cancer don't affect testamentary capacity unless they affect the brain.

Jane has motor neurone disease and can barely speak, but has full mental clarity. She has full capacity.

Misconception: "Someone lacking capacity under the Mental Capacity Act 2005 can't make a will."

Truth: Different test, different threshold. Someone who lacks capacity for day-to-day financial decisions may still have testamentary capacity to make a valid will.

The threshold is deliberately low. Most people have testamentary capacity unless there's specific evidence of inability to understand what a will does.

Protecting Your Will From Capacity Challenges

Six practical steps can ensure your will withstands future scrutiny.

Follow the golden rule if appropriate. If you're elderly (80+) or seriously ill, get a medical capacity assessment. The doctor should record findings in writing and keep them on file. Cost typically ranges from £500+ according to UK medical providers. Timing matters—assessment should happen as close as possible to will signing, ideally the same day or within a few days.

Use a professional will writer or solicitor. Professionals are trained to spot capacity concerns and create detailed attendance notes recording what you discussed, your understanding of your assets, your reasons for decisions, and your mental state and coherence.

These notes serve as powerful evidence if your will is later challenged. A solicitor's note might read: "Mrs. Smith clearly articulated her assets—house £300,000, savings £80,000. Named her three children unprompted. Explained she's leaving less to her eldest son due to their estrangement over the past five years. She was coherent, answered questions appropriately, and clearly understood the effect of her will."

Time it right. Make your will during periods of good health or clarity if capacity fluctuates. Don't wait until a crisis or terminal diagnosis if possible. If capacity is deteriorating, act quickly. Document the specific time and date of instruction-giving and signing.

Involve neutral witnesses. Witnesses should be independent—not beneficiaries or family. Choose witnesses who can later testify to your mental state if needed. Medical professionals, solicitors, or professional colleagues make particularly strong witnesses.

Keep medical records. Relevant medical records should be obtained and kept with the will file. GP records, hospital discharge summaries, and psychiatry notes if applicable provide context for any capacity assessment.

Consider video recording. Some practitioners now video-record will instructions. Video demonstrates the testator's coherence, understanding, and voluntary participation. It's not standard practice but increasingly recommended in case law, particularly for those with fluctuating capacity.

For straightforward situations where capacity is clear, WUHLD's online service provides a simple, affordable way to create your will at £99.99 versus £650+ for a solicitor. However, if you have concerns about capacity due to age, illness, or cognitive issues, we recommend consulting a solicitor who can assess capacity and follow the golden rule.

What Happens When a Will Is Challenged on Capacity Grounds?

Capacity challenges usually happen after death when the will is being probated. Anyone with standing can challenge—people who would be beneficiaries under an earlier will or under intestacy rules.

Courts consider medical evidence from GP records, hospital records, and expert psychiatric opinions. They review witness testimony from family, solicitors, witnesses, and carers. They examine the will itself to determine if it appears rational or bizarre. They evaluate evidence of the testator's understanding from solicitor's notes or medical assessments.

The timeline is lengthy. Capacity challenges can take 18-24 months to resolve. Legal costs often exceed £50,000-£100,000+ for contested probate.

If lack of capacity is proven, the will is invalid. The previous valid will takes effect if one exists. If there's no previous will, intestacy rules apply instead.

Success rates are very low. The presumption of capacity is strong, and courts have increasingly found in favour of testators having capacity, particularly where wills were professionally prepared.

Martin died at 86, leaving his £600,000 estate entirely to his new partner and excluding his three children. The children challenged on capacity grounds because Martin had Parkinson's and early dementia.

Evidence supporting capacity included the solicitor's detailed attendance notes and a GP assessment following the golden rule. Evidence against included GP records showing dementia diagnosis and family testimony about confusion.

The will was upheld. The presumption of capacity wasn't rebutted, and the golden rule assessment was thorough. But the litigation cost £85,000 in legal fees, took 20 months, and destroyed family relationships.

Following the golden rule and keeping good records prevents most challenges before they begin.

Understanding when you need professional help versus when an online will service is appropriate saves money while protecting your wishes.

You need professional legal advice if you:

  • Have diagnosed dementia, Alzheimer's, or cognitive impairment
  • Are over 80 years old
  • Have had a serious illness affecting your brain, such as stroke, brain injury, or severe mental illness
  • Take medication that affects cognition
  • Have family members who've expressed concerns about your mental state
  • Are making significant changes to a previous will
  • Expect your will to be challenged
  • Have a complex estate with business interests, overseas assets, or trusts

Online will services like WUHLD are suitable if you:

  • Are under 75 with no cognitive concerns
  • Have straightforward assets—house, savings, personal items
  • Have clear and uncomplicated wishes
  • Don't expect anyone to question your capacity
  • Want an affordable, efficient option at £99.99 versus £650+ for a solicitor

The decision framework is simple. Ask yourself: "Would anyone seriously question whether I understand what I'm doing?"

If the answer is no, an online will service is fine. If the answer is possibly or yes, seek professional legal advice and a golden rule assessment.

For the vast majority of people with clear capacity, WUHLD offers a straightforward, legally valid will. It takes 15 minutes online, costs £99.99 as a one-time payment with no subscriptions, and you can preview everything free before paying.

For complex situations or capacity concerns, professional legal advice is essential and worth the investment.

Frequently Asked Questions

Q: What does 'of sound mind' mean when making a will in the UK?

A: In UK law, 'of sound mind' means you have testamentary capacity—the mental ability to understand what a will is, what property you own, who should reasonably inherit from you, and the effects of your will. This is determined by the Banks v Goodfellow test from 1870, which remains the legal standard today.

Q: Do I need a medical assessment to prove testamentary capacity?

A: Not routinely, but it's recommended if you're elderly or seriously ill. The 'golden rule' from Kenward v Adams (1975) suggests that aged or ill testators should have their capacity assessed by a medical professional who records their findings. This typically costs £500+ excluding VAT for straightforward assessments.

Q: Can someone with dementia make a valid will in the UK?

A: Yes, potentially. Dementia doesn't automatically mean someone lacks testamentary capacity. The threshold is relatively low, and capacity can fluctuate—someone may have 'lucid intervals' where they understand enough to make a valid will. A medical assessment should evaluate capacity at the time instructions are given.

Q: What is the Banks v Goodfellow test for testamentary capacity?

A: The Banks v Goodfellow test requires you to: (1) understand the nature of making a will and its effects, (2) understand the extent of your property, (3) comprehend and appreciate who should reasonably inherit from you, and (4) have no mental disorder that prevents exercising your natural judgment about your estate. You must satisfy all four requirements.

Q: How do you challenge a will based on lack of capacity?

A: The challenger must provide evidence to raise 'real doubt' about the testator's capacity at the time the will was made. This shifts the burden back to those defending the will to prove capacity existed. Evidence includes medical records, witness statements, and expert opinions. However, there's a presumption of capacity if the will was properly executed and appears rational.

Q: What's the difference between testamentary capacity and the Mental Capacity Act 2005?

A: They're separate legal tests. Testamentary capacity follows the Banks v Goodfellow test from 1870, while the Mental Capacity Act 2005 applies to living persons making other decisions. The testamentary capacity threshold is lower—someone may have capacity to make a will but lack capacity under the MCA for other decisions like managing finances day-to-day.

Q: Can I make a will during a lucid interval if I have fluctuating capacity?

A: Yes. If your mental state fluctuates between confusion and clarity, a will made during a 'lucid interval' when you fully understood what you were doing can be valid. Medical professionals should assess and document your capacity at the specific time you give instructions and sign the will, not just generally.

Don't Let Capacity Concerns Stop You From Making Your Will

Understanding testamentary capacity removes the fear and uncertainty that stops too many older people from making wills. Whether you're 45 or 95, in perfect health or managing illness, what matters is that you understand your decisions at the moment you make them.

Don't let capacity concerns prevent you from protecting your family and making your wishes known.

Key takeaways:

  • Testamentary capacity means understanding what a will is, what you own, who should inherit, and the effects of your decisions—the threshold is deliberately low
  • The Banks v Goodfellow test from 1870 remains the only legal test, requiring you to meet all four criteria at the time you make your will
  • If you're elderly (80+) or seriously ill, follow the "golden rule" and get a medical capacity assessment (typically £500+) to protect your will from future challenges
  • Dementia, age, or physical illness don't automatically mean you lack capacity—many people with these conditions can make valid wills during lucid intervals
  • Properly executed wills benefit from a strong presumption of capacity—challenges require substantial evidence and rarely succeed

If you have clear mental capacity and straightforward wishes, WUHLD makes creating your will simple and affordable. For just £99.99—not £650+ for a solicitor—you can create a legally valid will in 15 minutes online with no appointments and no complexity.

You'll get your complete, legally binding will, a 12-page Testator Guide, a Witness Guide, and a Complete Asset Inventory document. Preview your entire will free before paying anything, with no credit card required.

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Legal Disclaimer: This article provides general information about testamentary capacity under UK law and does not constitute legal or medical advice. Testamentary capacity must be assessed on a case-by-case basis considering individual circumstances. For advice specific to your situation, please consult a qualified solicitor. If you have concerns about your capacity due to age, illness, or cognitive impairment, we recommend professional legal advice and medical assessment following the golden rule. WUHLD's online will service is suitable for straightforward UK estates where capacity is not in question; complex situations or capacity concerns require professional legal advice.

Information about medical conditions (dementia, Parkinson's, mental illness) is provided for general understanding only and does not constitute medical advice. Always consult qualified medical professionals for diagnosis and treatment.

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