Probate Litigation

California Will Contest or Trust Contest based on Mental Incapacity

By March 25, 2026No Comments
mental incapacity California

Table of Contents

Key Takeaways

  • A will or trust can be challenged if the person lacked mental capacity when it was signed.
  • California law presumes the person was competent, so the burden is on the person bringing the claim.
  • Lack of capacity focuses on whether the person understood their property, their family, and what they were signing.
  • Mental conditions, such as delusions, can invalidate a document if they affect its distribution.

What Is Mental Incapacity Under California Law?

To create a valid will or trust in California, a person must be at least 18 and of sound mind.
This means they must understand:
  • They are creating a will or trust
  • the nature of their property
  • Who their beneficiaries are
The standard is not high. A person does not need a perfect memory. But they must understand these basics at the time they sign.
When there are questions about whether these requirements were met, it may be necessary to take a closer look at the facts and evidence. At The Grossman Law Firm, we help beneficiaries evaluate whether a will or trust is legally valid and what steps can be taken next.

When a Will or Trust Can Be Invalid

A will or trust may be invalid if the person:

Did Not Understand What They Were Signing

If they did not understand they were distributing their property at death, the document may not be valid.

Did Not Understand Their Property or Family

Forgetting small details is normal. But failing to recognize major assets or close family members may indicate a lack of capacity.

Was Affected by Delusions or Mental Illness

A document may be challenged if a mental condition caused the person to distribute assets in a way they otherwise would not have.

How to Prove Lack of Mental Capacity in California

California law presumes capacity.
To succeed, you must show it is more likely than not that the person lacked capacity at the time the document was signed.
Common evidence includes:
  • Medical records
  • Prior versions of the will or trust
  • Witness testimony
Each case depends on the specific facts.
For more information on your specific case, contact an experienced litigation attorney today. The Grossman Law Firm has over twenty-five years of experience specializing in trust and probate litigation. If you are unsure about your next steps, contact The Grossman Law Firm today.

FAQ

What is testamentary capacity?

It is the legal ability to create a valid will or trust, including understanding the act, the property, and the people involved.

Is it difficult to prove a lack of capacity?

Lack of capacity can be difficult to prove. The law assumes the person was competent.

Does this apply to trusts, too?

Yes, the same principles generally apply to both wills and trusts in California.

How The Grossman Law Firm Can Help

Contesting a will or trust based on mental incapacity requires strong evidence and a clear understanding of California law.
At The Grossman Law Firm, attorney Scott Grossman handles probate and trust litigation matters throughout California. We help beneficiaries evaluate whether a document is valid and take action when necessary.
Call (888) 443-6590 or fill out our Get Help Now form. Our Intake Specialists can evaluate your case at no cost. Qualifying cases will be scheduled for a Free Phone Consultation with Attorney Scott Grossman.
Originally Published April 15, 2018