Litigation
Lack of Capacity to Sign a Trust or Will in California
California uses different capacity tests for a will and for a trust. A diagnosis of dementia is not, by itself, the end of the inquiry — and it is not irrelevant.
California measures capacity at the moment of signing, not by diagnosis alone. For a will, Probate Code §6100.5 requires understanding of the testamentary act, the property, and the people affected. For a trust, §§810–813 apply a sliding scale that tracks the complexity of the document. Dementia is evidence. It is not automatically incapacity.
Capacity to sign, California
- Wills
- Probate Code §6100.5 — nature of the act, the property, and the objects of bounty
- Trusts
- §§810–813 — capacity in light of the complexity of the decision
- When measured
- At the time of signing; lucid intervals are recognized
- Burden
- Generally on the person attacking a duly executed instrument
Capacity contests fail when they are argued as medical morality. They succeed when they are argued as a statute applied to a week in someone’s life. San Diego probate judges see dementia every calendar. What they want is the chart, the document, and what happened in the room when it was signed.
Wills: Probate Code §6100.5
To make a will, an individual must be able to understand the nature of the testamentary act, the nature and situation of their property, and their relation to the living persons whose interests are affected. That is a lower bar than the capacity to enter a complex contract. It is also not nothing. A person who cannot identify their children, or who believes the house was already sold when it was not, is not a person who meets §6100.5 on that day.
Trusts: a sliding scale
Probate Code §§810–813 reject a single capacity standard for all acts. Capacity is evaluated in light of the complexity of the decision. A one-page amendment changing a successor trustee is not the same act as a restatement that rewires tax formula clauses and disinherits a child. Contestants who treat every trust signing as if it were a will, and defenders who treat every dementia diagnosis as irrelevant, both lose cases they should have won.
| Act | Capacity lens | Typical proof |
|---|---|---|
| Simple will or pour-over | §6100.5 | Medical chart + drafting notes from the signing week |
| Trust amendment (successor trustee) | Lower complexity under §§810–813 | Was the settlor oriented to that decision? |
| Full restatement / tax trust | Higher complexity | Could they understand the scheme, not just the signature page? |
Evidence that actually moves the needle
- Contemporaneous medical records — MMSE or MoCA scores, medication lists, notes about confusion or hallucinations in the days around the signing.
- The drafting attorney’s file. A careful lawyer meets the client alone, documents the conversation, and will testify. A lawyer who took instructions from the beneficiary and never met the settlor without that person in the room has a different file.
- Prior estate plans, to show whether this document is a continuation or a rupture.
- Lay testimony about bills, driving, and whether the settlor could still manage a checkbook. Lay observations are admissible and, in the right case, more persuasive than a hired expert who never met the person.
Capacity and undue influence travel together
A weakened person is both more likely to lack capacity and more susceptible to influence. Petitions routinely plead both. The court can invalidate a document on either ground. See undue influence in a California trust or will and how to contest a trust. If you are holding a late restatement and a diagnosis, do not wait for a perfect expert report before you calendar the contest deadline. Call (858) 248-2779 or request a consultation.
This article is general information about California law, not legal advice, and reading it does not create an attorney–client relationship. Trust and probate deadlines are strict and many rights are lost by missing one — for guidance on your own situation, contact Tresp Law, APC or call (858) 248-2779.
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Common questions
Frequently asked
What is the capacity test for a California will?
Probate Code §6100.5: the individual must understand the nature of the testamentary act, the nature and situation of their property, and the relation to the people who are affected by the will. A diagnosis is evidence, not the test.
Is the test the same for a trust?
No. Capacity to execute a trust is evaluated in light of the complexity of the document (Probate Code §§810–813). A simple restatement that mirrors a long-standing plan is not judged the same way as a sophisticated tax-driven irrevocable trust.
Can someone with dementia still sign?
Sometimes. Capacity is time-specific. A person may have a lucid interval. The relevant question is capacity at the moment of signing, which is why the drafting attorney’s notes and the medical chart from that week matter more than a diagnosis from two years earlier.
Who has the burden of proof?
A duly executed will or trust is generally presumed valid. The contestant must prove lack of capacity. When the instrument is the product of a confidential relationship and other suspicious circumstances, related presumptions (including §21380) can shift burdens on undue-influence counts even if capacity is disputed too.
This page is general legal information, not legal advice, and does not create an attorney-client relationship. California trust and probate law is fact-specific and deadlines are unforgiving — please speak with a qualified attorney about your own circumstances.
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