How Do You Know Someone Can Make a Valid Will?

When someone decides to make or change a Will, most families focus on who gets what. The courts start somewhere very different – could this person legally understand what they were doing at the time?

That question, known as testamentary capacity, can decide whether a Will stands or falls. If it’s not considered properly, even a carefully drafted Will can be torn apart later. Families end up in conflict. Estates get tied up in costly legal action.

Key points:

• Testamentary capacity is the legal ability to make or amend a valid Will
• The leading test comes from Banks v Goodfellow (1870) and still applies today
• The person must understand what a Will does, what they own, and who might expect to benefit
• Capacity is decision specific and time specific, even for people with dementia
• If someone lacks capacity, the Court of Protection can make a statutory Will instead
• Independent testamentary capacity assessments help prevent disputes and protect families and professionals

What is Testamentary Capacity?

Testamentary capacity is the legal and mental ability a person must have to make or change a valid Will in England and Wales. It’s not about whether others agree with the decisions. It’s about whether the person understood what they were doing, in broad terms, at the time they signed.

A Will made without testamentary capacity is likely to be invalid. That means the estate could fall back to an earlier Will or the intestacy rules instead. It completely changes who inherits, and it’s a common trigger for bitter probate disputes.

The Banks v Goodfellow test explained

The leading test for testamentary capacity still comes from a Victorian case, Banks v Goodfellow (1870). The courts continue to rely on it when deciding whether a Will is valid. For someone to have testamentary capacity they must be able to:

Understand that they are making a Will and what a Will does – namely disposing of their estate on death.

Understand, in broad terms, the nature and extent of the property they are leaving – they don’t need to know exact figures, but they should grasp what they own.

Understand who might reasonably expect to benefit from their estate – for example, close family – and be able to weigh those claims, even if they choose not to leave them anything.

Make choices that are not driven by a mental disorder or delusion – decisions shouldn’t be distorted by false beliefs that affect how they distribute their estate.

This is a legal test, not just a medical one. A diagnosis such as dementia or brain injury may raise concerns, but it doesn’t automatically mean someone lacks testamentary capacity. What matters is what the person could understand, retain, weigh and communicate at the time the Will was made.

How the Mental Capacity Act fits in

Alongside Banks v Goodfellow sits the Mental Capacity Act 2005 (MCA), which provides the general framework for decision-making capacity in England and Wales. The MCA is built on five key principles, including the presumption of capacity and the need to support people to make their own decisions wherever possible.

Under the MCA, a person lacks capacity for a specific decision if, because of an impairment of the mind or brain, they are unable to:

• Understand the relevant information
• Retain that information long enough to use it
• Weigh it as part of the decision-making process
• Communicate their decision in any recognisable way

For statutory Wills (where the Court of Protection steps in because someone lacks capacity to make their own Will), the Court applies the MCA test, then uses the MCA best interests framework to decide what the Will should say.

There’s ongoing discussion in legal circles about aligning all testamentary capacity decisions with the MCA, but Banks v Goodfellow remains the main common law test applied to Wills that people make themselves.

Dementia, fluctuating capacity and timing

Families are often told “Mum has dementia, she can’t make a Will”. That’s too simplistic and, in many cases, just wrong. Capacity is:

Decision specific – someone may lack capacity for a complex financial transaction but still have capacity to make a relatively straightforward Will.

Time specific – capacity can improve or deteriorate over time, and can vary within a day depending on fatigue, medication, or environment.

A person with dementia may still have testamentary capacity, provided they can meet the Banks v Goodfellow test when they sign the Will. Good professional practice recognises this. That’s why careful timing, calm surroundings, and clear explanations are so important when assessing capacity.

Why testamentary capacity matters so much

Getting testamentary capacity wrong can have serious consequences for everyone involved. Common risks include:

• A Will being thrown out because the person lacked capacity when it was made, putting the estate back under an earlier Will or intestacy
• Costly, protracted disputes between family members, with legal costs paid out of the estate
• Allegations of undue influence or exploitation where there was no clear, independent evidence of capacity at the time

On the other hand, when capacity is clearly considered and documented, it can:

• Protect the person’s true wishes, even after they are no longer able to explain themselves
• Give solicitors, professional deputies and executors confidence that they are relying on a valid Will
• Reassure relatives that decisions were made fairly, not stitched up behind closed doors

For families already under emotional strain, this can be the difference between a relatively smooth administration and years of ongoing conflict.

When the Court of Protection makes a Will

If someone genuinely lacks testamentary capacity and needs a Will to be created or updated, the Court of Protection can authorise a “statutory Will”. This usually arises where:

• There is no existing Will, or the existing Will is obviously out of date
• The person’s circumstances have changed significantly (for example, inheritance, relationship breakdown, or long-term care)
• There is a need to protect the person’s estate or resolve uncertainties that could otherwise lead to disputes

In such cases, the Court looks at best interests under the MCA, including the person’s past and present wishes and feelings, their values, and the views of those close to them, before deciding what the Will should contain. Robust, independent capacity evidence is central to this process, both to confirm that the person cannot make the decision themselves and to help the Court understand their story.

The value of independent testamentary capacity assessments

Where there is any real doubt, many careful practitioners use what is often called the “Golden Rule” – arrange a thorough, contemporaneous capacity assessment when an older or vulnerable person makes a Will. In practice, an independent testamentary capacity assessment should:

• Test the person’s understanding against the Banks v Goodfellow criteria, using the language and principles of the MCA
• Explore and record any diagnosis, impairments and how these affect decision-making, rather than relying on labels alone
• Check for signs of pressure, undue influence or delusions affecting the person’s choices
• Produce a clear, structured report that can be understood by the family, the drafting solicitor and, if needed, a court

A short GP note may be helpful, but it often focuses on diagnosis, not the legal tests for capacity. A specialist Mental Capacity Act assessment goes further, translating clinical information into a legally robust opinion about testamentary capacity.

Why instruct AJH Social Work for testamentary capacity

AJH Social Work provides independent Mental Capacity Act assessments for a wide range of decisions, including testamentary capacity, capacity to gift, deputyship and LPA certification. This independent position offers several advantages over relying solely on local authority staff or a brief medical letter:

Independence and neutrality – AJH is not part of the family, the local authority, or any care provider. Assessments are focused solely on the person’s rights and the legal tests that must be satisfied.

Legally literate reports – With a strong grounding in both social work and law, reports are written to stand up to scrutiny in the Court of Protection or contentious probate proceedings, clearly linking evidence to Banks v Goodfellow and the MCA.

Person-centred practice – Assessments are carried out in a way that is respectful, accessible, and sensitive to fluctuating capacity, communication needs, and the realities of family life.

For solicitors and professional deputies, this provides the defensible evidence they need to manage risk. For families, it offers reassurance that a loved one’s Will reflects their wishes, not someone else’s agenda.

Practical advice for families and professionals

If you are worried about whether someone has testamentary capacity, consider:

Seeking early advice – Speak to a solicitor and, where there is any doubt, arrange an independent capacity assessment before the Will is signed.

Timing and environment – Choose a time of day when the person is usually at their best, and minimise distractions, fatigue and pressure.

Recording the process – Encourage the solicitor and assessor to keep detailed attendance notes and a clear written opinion on capacity, in case questions are raised later.

If you are a solicitor or professional deputy working on a high-risk or sensitive case, bringing in an independent Mental Capacity Act specialist can save a great deal of grief, time and cost down the line.

If you would like to discuss a testamentary capacity assessment, AJH Social Work can talk through the situation in plain English, outline realistic options, and help you decide whether a formal assessment is needed in your particular case.

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