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Can I challenge a Will signed by someone with dementia?

Will Disputes

Dementia is one of the most common grounds for contesting a Will in Queensland. However, a medical diagnosis of cognitive decline or dementia does not automatically mean a Will is invalid. The law distinguishes between a medical condition and legal capacity, focusing strictly on the testator’s state of mind at the exact moment they executed the document.

To make a valid Will in Queensland, the testator must possess “testamentary capacity.” The foundation for assessing capacity is the historic common law test established in the 1870 English case of Banks v Goodfellow.1

Under this test, the testator must:

  1. Understand the nature of the act: They must know they are making a Will and understand what that document does (i.e., disposing of their assets upon death).
  2. Understand the extent of their estate: They must have a general understanding of the assets they own (such as property, bank accounts, or shares) and their approximate value.
  3. Comprehend the claims upon their estate: They must appreciate who would normally expect to inherit from them (such as a spouse, children, or dependants) and weigh the merits of giving to or excluding those individuals.
  4. Be free from any disorder of the mind: They must not suffer from a delusion or mental illness that influences or poisons their mind to make dispositions they would not otherwise have made.

A critical misunderstanding is that a medical diagnosis of dementia automatically invalidates a Will. Legal capacity is decision-specific and time-specific.

Under Queensland law, capacity can fluctuate. A person with mild or moderate dementia may experience “lucid intervals”—periods of clarity during which they are fully capable of understanding their actions and meeting the Banks v Goodfellow criteria.

As confirmed by the Supreme Court of Queensland in Re B,2 a court will assess the testator’s capacity at the precise time the Will was signed. If the testator had capacity at that moment, the Will remains valid even if their cognitive function was severely impaired shortly before or after.

Aspect Medical Diagnosis (Dementia) Legal Testamentary Capacity
Who Determines It Geriatrician, neurologist, or GP A Solicitor (initially) or a Judge (in a dispute)
Focus General cognitive decline and physical brain changes Ability to understand a specific transaction at a specific time
Binary vs. Specific Often diagnostic (you have it or you don’t) Decision-specific (may have capacity for a Will, but not a business contract)
Fluctuation Acknowledged, but the underlying condition remains Directly relevant: “lucid intervals” can support legal validity

How to Protect a Will When Dementia is Present

If a family member has been diagnosed with cognitive decline or early-stage dementia and wishes to update or make a Will, several precautionary steps should be taken to prevent future disputes:

  1. Obtain a Professional Capacity Assessment: Engage a geriatrician to conduct a formal capacity assessment specifically addressing the four limbs of the Banks v Goodfellow test. The doctor should provide a written report certifying the testator’s capacity on or immediately prior to the day of signing.
  2. Engage an Experienced Solicitor: Do not use a DIY Will Kit. A solicitor will take detailed, contemporaneous notes of the instructions, asking open-ended questions designed to test the client’s understanding of their assets and beneficiaries.
  3. Document the Witnessing Process: In some cases, having a medical practitioner act as one of the witnesses can provide valuable supporting evidence. Contemporaneous letters or statutory declarations from the witnesses confirming the circumstances can also protect the Will from future challenges.3

How to Challenge a Will Due to Lack of Capacity

If you believe a deceased relative did not have the required capacity when they signed their Will, you must act quickly.

In Queensland, you should notify the executor or administrator of your intention to challenge the Will before probate is granted. If probate has already been applied for, you can file a “caveat” in the Supreme Court of Queensland to halt the process while the capacity dispute is investigated.4

If the court declares a Will invalid due to a lack of capacity, the estate will typically be distributed under the terms of the testator’s previous valid Will. If there is no previous valid Will, the estate will be distributed according to the rules of intestacy under Schedule 2 to the Succession Act 1981 (QLD).5

Strict Time Limits Apply In Queensland, you generally have a limited window to contest a Will. For family provision claims, you must give notice of your claim within six months of the date of death and commence proceedings within nine months. For capacity challenges, it is critical to act before probate is granted and the estate is distributed. Contact Bell & Senior Lawyers immediately for a confidential consultation at (07) 5532 8777.

Professional Guidance

Estate disputes are emotionally taxing and legally complex. The team at Bell & Senior Lawyers provides compassionate, clear legal advice to help families resolve Wills and estates matters.

📞 (07) 5532 8777 | 🌐 bellsenior.com.au | Contact us

  1. Banks v Goodfellow (1870) LR 5 QB 549. ↩︎

  2. Re B [2010] QSC 290. ↩︎

  3. Succession Act 1981 (Qld) s 10. ↩︎

  4. Uniform Civil Procedure Rules 1999 (Qld) r 624 (caveats in probate proceedings). ↩︎

  5. Succession Act 1981 (Qld) sch 2 (distribution of intestate estates). ↩︎

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