What is Testamentary Capacity? A Guide for Singapore Residents

Testamentary capacity is the legal term for the mental ability required to make a valid will. If a person lacks testamentary capacity at the time they sign a will, the will can be challenged in court and declared void — resulting in the estate being distributed as if no will existed.

In Singapore

Singapore follows the classic four-part test for testamentary capacity established in Banks v Goodfellow (1870), which Singapore courts have consistently applied:

To have testamentary capacity, the will-maker must, at the time of signing:

1. Understand the nature of making a will and what it does
2. Understand the extent of the property being disposed of
3. Understand the claims of people who might reasonably expect to benefit (typically family members)
4. Not be suffering from a disorder of the mind that poisons their affections, perverts their sense of right, or prevents the exercise of their natural faculties

Note that this is a functional test — it is about what the person understood and could do at a specific moment, not about a medical diagnosis.

Capacity vs Diagnosis

A person with a dementia diagnosis does not automatically lack testamentary capacity. What matters is their mental state at the specific time the will was executed. Many conditions involve fluctuating cognitive states — a person may have adequate capacity on a clear day even if they generally have impaired cognition.

Conversely, a person without any diagnosis can still lack testamentary capacity if, at the moment of signing, they were under the influence of medication, severely unwell, or otherwise unable to meet the four-part test.

Why Wills Get Challenged

Testamentary capacity challenges typically arise when:

• The will was made late in life or during serious illness
• The will favours one person (especially a caregiver or recently met individual) to the disadvantage of previously expected beneficiaries
• The will significantly differs from a prior will without obvious explanation
• Family members were excluded without apparent reason

The courts will look at evidence of the will-maker’s mental state around the time the will was signed — medical records, witness testimony, the will-maker’s behaviour, and the circumstances of the will’s creation.

Protecting Capacity

The most practical step is making a will — and reviewing it — while in obvious good health. A will made at 45 when healthy is far less vulnerable to a capacity challenge than one made at 78 during a serious illness.

If a will is made during illness or at advanced age, having a medical professional assess and document capacity contemporaneously provides significant legal protection. Some solicitors will recommend this for clients in their 70s or 80s or during serious illness.

Advisor Perspective

I consistently encourage clients in their 40s and 50s to treat estate planning as a proactive exercise rather than a crisis response. One of the underappreciated benefits of this timing is that wills made in clear health are essentially unchallengeable on capacity grounds. A will made at 50 is a very different legal document from the same will made at 80 — not in content, but in vulnerability to challenge.

Common Mistakes

Waiting until a health crisis to make a will. The period when people most want to get their affairs in order is also the period when a will is most vulnerable to challenge.

Not documenting capacity when making a will later in life. A medical assessment at the time of will-making — even a brief one — can be the evidence that closes off a capacity challenge.

Assuming a witnessed will is automatically valid. Witnesses confirm the signature but not the capacity. Capacity is a separate requirement from proper execution.