Can you legally challenge a Will over ‘lack of testamentary capacity?’

24 August 2026

A lack of testamentary capacity is applied to an individual who does not have the mental soundness needed to make or change their Will.

People might challenge a Will if they believe the person making or changing it was vulnerable at the time of signature.

While the impairment might not be permanent, it might have impacted an individual at the point at which a Will was made.

If this is the case, a Will might be challenged by those who believe inheritance losses were brought about with clouded judgement.

How is a ‘lack of testamentary capacity’ tested?

The legal test for assessing whether someone has the mental capacity to make or change a Will was set out in the Banks v Goodfellow case.

Despite being more than 150 years old, this landmark English case set the precedent for how testamentary capacity is defined.

To have the capacity to make a valid Will, a person needs to:

• Understand the nature of making a Will and what it does.
• Know the extent and value of the property they are giving away.
• Recognise the people who would normally inherit from them.
• Have no disorder of the mind or insane delusions that poison their view or cause them to make a choice they would not normally make.

The testator, the person making the Will, must understand their actions, what they own and who they want to leave it to, according to the first three criteria.

While an individual might understand each aspect of their Will and the implications, mental conditions might mean that they are not able to make a rational decision.

Conditions and circumstances that might fall under this scope are dementia, schizophrenia, bipolar disorder, substance abuse and delirium, among others.

Aside from legal recognition, ensuring a testator meets these conditions can prevent manipulation and safeguard their true intentions.

Challenging testamentary capacity

Someone might want to challenge a will based on a testator’s mental capacity if they believe the deceased was vulnerable and potentially manipulated to alter inheritance.

When disputing a Will, a place to start might be entering a caveat to prevent the grant of probate during investigations, which is normally valid for six months.

The next step in lodging a challenge is to gather evidence, including medical records, GP notes, witness statements and video or audio recordings.

As courts generally presume that a testator was capable at the time their will was made, the burden of proof falls on the challenger.

Where a challenger has gathered enough evidence to raise doubts regarding capacity, the burden is then shifted to supporters of the Will to refute claims.

Challenging testamentary capacity can result in both Alternative Dispute Resolution (ADR) and litigation, but ADR is normally the starting point.

If a settlement isn’t found through mediation and hostilities escalate, disputes might need a formal Court Order to reach a resolution.

Speak to our Civil Disputes Team

Our Civil Dispute Team can help you challenge a Will you believe to be invalid due to a lack of testamentary capacity.

We can evaluate the strength of your legal position and whether there is a realistic case to be made, gathering any supporting evidence.

During mediation and court proceedings, our legal experts can represent your interests and help present the strongest case.

Challenging testamentary capacity is often a difficult conversation, so seeking guidance at the earliest stage can make sure it’s done right.

If you are worried a Will was made without the necessary mental capacity, speak to our Civil Disputes Team for expert advice.