Does a dementia diagnosis invalidate a will in California?

No, not by itself. Probate Code section 810 states a rebuttable presumption that all persons have capacity and confirms that someone with a mental or physical disorder may still be capable of executing wills or trusts. Section 811 requires evidence of a functional deficit and its correlation to the act.

What is the test for testamentary capacity in California?

Under Probate Code section 6100.5, an individual is not competent to make a will if they cannot understand the nature of the testamentary act, understand and recollect the nature and situation of their property, or remember and understand their relations to living descendants, spouse, parents and those affected.

Is the capacity standard the same for a trust as for a will?

Not necessarily. Section 6100.5 sets the standard for wills. Sections 810 to 812 supply the general framework, and section 812 applies except where otherwise provided, including by the statutory and decisional law of testamentary capacity. Which standard applies depends on the document and its complexity.

What evidence proves lack of capacity?

Medical records close in time to the signing, the drafting attorney's notes and file, testimony from people who saw the person that week, and the circumstances of the signing itself. The correlation section 811 requires is what turns a diagnosis into proof.

Lack of Capacity in California

California presumes everyone has capacity. To set aside a will or trust for incapacity you must show a deficit in a mental function listed in Probate Code section 811 and a correlation between that deficit and the document signed. A dementia diagnosis alone does not meet the test.

A framed portrait of an older person on a side table beside a pair of reading glasses and a folded newspaper. — The question is never whether they were declining. It is what they understood on the day they signed.

The presumption runs against you, and the statute says why

California starts from the opposite of what most families assume. Probate Code section 810 declares a rebuttable presumption affecting the burden of proof that all persons have the capacity to make decisions and to be responsible for their acts, and states expressly that a person with a mental or physical disorder may still be capable of executing wills or trusts. It goes further: a determination of incapacity should rest on evidence of a deficit in one or more mental functions rather than on a diagnosis. Section 811 then supplies the structure: a finding must be supported by evidence of a deficit in at least one listed mental function — alertness and attention, information processing, thought processes, or mood and affect — and by evidence of a correlation between that deficit and the act in question. For wills, section 6100.5 sets the standard: the individual must understand the testamentary act, recollect the nature and situation of their property, and understand their relations to those affected.

Sources: Probate Code s.810 - Presumption of capacity · Probate Code s.811 - Mental function deficits and the required correlation · Probate Code s.6100.5 - Capacity to make a will · Verified 2026-08-17.

What section 811 actually lists

Mental function	Examples the statute gives
Alertness and attention	Level of arousal or consciousness; orientation to time, place, person and situation; ability to attend and concentrate
Information processing	Short- and long-term memory; ability to understand or communicate; recognition of familiar persons and objects; ability to understand quantities; ability to reason logically
Thought processes	Severely disorganised thinking; hallucinations; delusions; uncontrollable, repetitive or intrusive thoughts
Mood and affect	A pervasive, persistent or recurrent state such as euphoria, anger, anxiety, fear, panic, depression, hopelessness, helplessness or apathy

Correlation is where these cases are won and lost

Families routinely arrive with a diagnosis and expect it to be decisive. It is not, and section 810 says so directly. The work is connecting a specific deficit to the specific act — that the memory failure meant they could not recollect what they owned, or that a documented delusion about a particular child is what produced the disinheritance. Section 6100.5 also reaches that second situation independently: a will is invalid where a mental health disorder producing delusions or hallucinations caused the person to devise property in a way they otherwise would not have.

Capacity and undue influence are different claims

They are frequently pleaded together and are often confused. Incapacity says the person could not form the intention. Undue influence says they could, but someone else’s pressure supplanted it. A person with full capacity can be unduly influenced, and the evidence that supports one claim frequently supports the other — which is why the two are usually investigated as one exercise.

Need help with legal fees?

We litigate select cases on contingency, with no upfront fees.

Costs are separate from the fee, and whether you are responsible for them is set out in the written agreement before you sign anything.

You pay no fee unless there is a recoveryThe firm carries the risk of the case. If nothing is recovered, no fee is owed.

The rate is negotiable, and must say soCalifornia requires the written agreement to state that the fee is not set by law.

Costs are separate, and disclosed up frontThe agreement must state how costs affect the fee before you sign it.

How contingency fees work in California

A contingency fee means the attorney is paid from what is recovered rather than by the hour, so a beneficiary who cannot fund litigation out of pocket can still bring a claim. California regulates these agreements closely. Under Business and Professions Code section 6147, the agreement must be in writing and the attorney must give the client a duplicate copy, signed by both, when the contract is made. It must state the agreed contingency rate; how disbursements and costs incurred in prosecuting or settling the claim will affect that fee; and to what extent the client could be required to pay for related matters. Unless the matter falls under section 6146, the agreement must also state that the fee is not set by law and is negotiable. These are not formalities: failure to comply with any provision of section 6147 makes the agreement voidable at the client’s option, leaving the attorney entitled only to a reasonable fee.

Sources: Business and Professions Code s.6147 - Contingency fee contracts · Verified 2026-08-03.

Not every matter suits a contingency arrangement, and the firm does not take every case on one. Whether yours qualifies depends on the facts, the likely recovery, and the assets actually available to satisfy a judgment. Ask when you call.

We Answer 24/7 — Call Anytime · (415) 275-1492