# Undue Influence: Definition and How It Works in California

> Undue influence is excessive persuasion that overcomes a person's free will, the top ground for contesting a will or trust.

Source: https://ridleylawoffices.com/estate-planning-glossary-california/undue-influence/

By Eric Ridley, attorney, Ridley Law. Updated September 2026.

**Undue influence** is excessive persuasion that overcomes a person’s free will and substitutes another person’s intent for their own, the most common ground for contesting a California will or trust.

## How it works in California

Prob. Code, § 86 adopts the definition in Welf. & Inst. Code, § 15610.70: excessive persuasion “that causes another person to act or refrain from acting by overcoming that person’s free will and results in inequity.” [What undue influence means under Probate Code section 86](https://ridleylawoffices.com/undue-influence-probate-code-86-california/) lays out the factors courts weigh, including the vulnerability of the person influenced and the tactics used against them.

Some gifts trigger a legal presumption of undue influence rather than requiring the challenger to prove it directly. Under Prob. Code, § 21380, a gift to the person who drafted the document, a care custodian, or certain other people in a position of trust is presumed the product of undue influence, and the burden shifts to them to disprove it. See [the presumption of undue influence under section 21380](https://ridleylawoffices.com/presumption-undue-influence-21380-california/) for who it covers.

Undue influence is not the same as ordinary persuasion. A spouse or child who argues for a larger share, or who cares for a parent and is later remembered generously, has not necessarily done anything wrong.

## Why it matters

For example, a caregiver who isolates an elderly person from family and then becomes the sole beneficiary of a late amendment fits the pattern courts look for, even without direct proof of specific threats or promises.

## Common mistakes

Families sometimes label any unequal distribution as undue influence, when unequal is not automatically improper. Others wait too long to raise it, past the deadline that applies to a trust or will contest.

## Related terms

- [No-Contest Clause](https://ridleylawoffices.com/estate-planning-glossary-california/no-contest-clause/): can discourage an undue influence claim that lacks probable cause.
- [Testamentary Capacity](https://ridleylawoffices.com/estate-planning-glossary-california/testamentary-capacity/): a related but distinct ground, often argued alongside undue influence.
- [Trust Contest](https://ridleylawoffices.com/estate-planning-glossary-california/trust-contest/): the proceeding where an undue influence claim is usually raised.
- [Will Contest](https://ridleylawoffices.com/estate-planning-glossary-california/will-contest/): a court challenge to the validity of a will.

Part of the [California estate planning glossary](https://ridleylawoffices.com/estate-planning-glossary-california/). For the full treatment, see [What Is Undue Influence Under Probate Code § 86](https://ridleylawoffices.com/undue-influence-probate-code-86-california/).