Lack of Testamentary Capacity

While California presumes that most adults have the testamentary capacity, or ability, to understand and write their own will, some exceptions can be demonstrable. In California, somebody may not be mentally competent—or “of sound mind”—to write a will if:

  • They do not understand the nature of the testamentary act. In other words, they do not understand what they are doing by writing or signing a will.
  • They do not have a complete understanding of their assets, properties, accounts, and material possessions.
  • They do not remember or understand their relationship to living descendants—their spouse, parents, children, grandchildren, or anyone else whose interests may be affected by the creation of a will.

California law also allows a person’s testamentary capacity to be challenged if they have a mental illness with symptoms including delusions and/or hallucinations, provided that such delusions and/or hallucinations result in their inability to understand their will and its consequences.

Undue Influence

If someone was under “undue influence” when they wrote a will, it means that another person’s persuasion caused them to act—or refrain from acting—of their own free will.

Undue influence may exist if and when:

  • The will writer, or testator, was unusually vulnerable, perhaps due to old age, mental impairment, isolation, or emotional distress.
  • The influencer, perhaps a caretaker or guardian, used their authority or abused that position to influence the terms of the will.
  • The influencer used negligent or coercive tactics such as withholding medication or refusing a person visitation rights to their grandchildren.

You may be able to make other arguments to show undue influence. However, an accusation of undue influence requires sufficient evidence to persuade a judge of its existence.

The Will Was Not Valid

If the will was not signed or is otherwise not compliant with state law, you may be able to have the will overturned. However, the dissolution of a will may compel the probate court to parcel inheritances based on a strict legal formula. This legal formula benefits close blood relations.


Sometimes, a will is created through an act of fraud. A will may have been written by a person other than the deceased, or an individual may have provided the testator with false information intended to sway their allocation of inheritances.

How to Challenge a Will

You cannot challenge a will if you do not have the grounds to do so. In most cases, the court will not entertain an argument that a will should be overturned simply because its allocation of assets does not seem fair. You will have to challenge the will on strictly legal grounds.

Challenging a will can be difficult because you need definite evidence to show that the testator lacked capacity to understand their will, was unduly influenced, or was the victim of fraud. This means collecting documents, medical reports, and other proof for the probate court.

If you are planning to challenge a will, you should only do so after contacting an attorney with special probate litigation experience.


Philip J. Kavesh
Nationally recognized attorney helping clients with customized estate planning guidance for over 40 years.