Yes. A Missouri durable power of attorney can be invalidated, but the path depends on what is actually wrong. Sometimes the document itself was never valid — the person who signed it lacked capacity, the paperwork skipped a required formality, or someone procured it through fraud or pressure. Other times the document is perfectly valid and the problem is the person holding it: an agent who skims accounts, deeds the house to himself, or ignores the principal's instructions.

Those are different fights with different remedies. This guide separates them. You will learn what Missouri law requires for a valid durable power of attorney, the five grounds that void the document itself, how courts deal with an agent who abuses a valid document, who can bring a challenge, and what proof it takes. If you are worried about a parent, a spouse, or your own plan, start here.

A durable power of attorney is built to survive incapacity

A power of attorney is a written document in which one person, the principal, authorizes another person, the attorney in fact, to act on the principal's behalf. The attorney in fact can sign checks, pay bills, manage investments, and handle real estate — whatever the document allows.

Ordinary agency ends when the principal loses capacity. A durable power of attorney exists precisely to defeat that rule. Under RSMo 404.705, Missouri's Durable Power of Attorney Law, the agent's authority continues even if the principal becomes disabled or incapacitated, as long as the document meets three requirements:

It is labeled a "Durable Power of Attorney."
It states that the agent's authority will not end if the principal becomes disabled or incapacitated.
The principal signs and dates it and acknowledges it before a notary, using the same formality Missouri requires for a deed to real estate.

A durable power of attorney does not need to be recorded to be valid. Section 404.705, RSMo, also makes the agent's authorized acts binding on the principal even after the principal loses capacity.

This design has a consequence that surprises many families: the principal's later decline is not a ground for invalidation. The whole point of the instrument is to keep working after dementia, a stroke, or an injury. If your mother signed a proper durable power of attorney in 2019 and her memory failed in 2024, her 2024 condition does not void the 2019 document. The questions that matter are what happened at signing and what the agent has done since.

Five grounds can invalidate the document itself

Attacking the document means proving it was never valid or that the principal lawfully ended it. Missouri recognizes five grounds.

1. The principal lacked capacity when signing. Capacity is measured at the moment of execution, not before or after. Missouri's test, stated in Murphy v. Carron, 536 S.W.2d 30 (Mo. banc 1976), asks whether the signer could understand the nature and consequences of the transaction. A person in the early stages of dementia may still pass that test on a good day, and a diagnosis alone does not prove incapacity. Medical records, the drafting lawyer's notes, and witnesses to the signing usually decide the question.

2. The execution was defective. Missouri requires a signed, dated, notary-acknowledged writing. A power of attorney that was never acknowledged, or one the principal never signed, fails the statutory requirements and can be declared invalid.

3. Fraud or forgery. A document the principal never agreed to — a forged signature, pages swapped after signing, or a signer deceived about what the document was — is void.

4. Undue influence. Pressure that overpowers the signer's free will invalidates the document. Because an attorney in fact occupies a position of trust, Missouri courts treat the relationship as confidential; when the person who benefits from the document also helped procure it, suspicion arises and the burden can shift to the beneficiary to show the transaction was fair and freely made.

5. The principal revoked it. A principal who still has capacity can revoke a durable power of attorney at any time. Once revoked, the agent's authority is gone, whatever the document says.

One myth deserves a direct answer: a power of attorney is not invalid because it conflicts with a will or trust. The documents do different jobs. A power of attorney operates during your life; a will operates after your death. An agent who drains accounts can reduce what your heirs receive, but that is an abuse-of-authority problem — the subject of the next section — not a conflict that voids the instrument.

A valid document can still have a rogue agent

Most family crises involve a valid document in the wrong hands. Missouri law treats the attorney in fact as a fiduciary. Under RSMo 404.710, an agent holding general powers must follow the principal's instructions, act in the principal's interest, and act in good faith and with prudence.

The statute also fences off the most dangerous powers. Section 404.710, RSMo, allows an agent to make gifts, change survivorship interests, or amend trusts only when the document expressly authorizes those acts. General language granting "all lawful powers" is not enough.

Missouri's Supreme Court enforced that limit in Hightower v. Myers, 304 S.W.3d 727 (Mo. banc 2010). An agent used a statutory-form durable power of attorney to transfer the principal's real estate to himself. The court held that the form's general powers did not include the power to make gifts, so the self-transfer exceeded the agent's authority. The lesson cuts two ways: the transfer could be undone, but the power of attorney itself remained valid. When the agent is the problem, the remedy targets the agent's acts — reversing transfers, recovering funds, removing the agent — not the document.

If an agent is taking money or property, that conduct may also support claims for breach of fiduciary duty and conversion, and it is worth reporting as suspected elder financial exploitation.

Missouri courts can step in while the principal is alive

You do not have to wait for the principal's death to act. RSMo 404.727 gives the probate division of the circuit court direct authority over durable powers of attorney.

First, the accounting. Section 404.727, RSMo, lets the principal demand a formal accounting from the attorney in fact. If the principal is disabled, incapacitated, or deceased, the principal's legal representative, an adult member of the principal's family, or any person interested in the principal's welfare may file the petition. An accounting forces the agent to produce records and explain every transaction.

Second, the court's intervention powers. If the principal is disabled or incapacitated, the same statute lets the court, for good cause shown:

Order the agent to exercise — or stop exercising — authority in a particular way
Modify the agent's authority
Terminate the durable power of attorney
Remove the attorney in fact
Confirm a successor agent's authority
Appoint a guardian or conservator for the principal under Chapter 475, RSMo

If the evidence shows the agent has breached a fiduciary duty, or is reasonably likely to do so soon, the court can suspend or modify the agent's authority after notice and hearing. Guardianship or conservatorship is the heavier remedy: the court takes over the decision-making structure entirely. Families often use a 404.727 petition to remove an abusive agent and a Chapter 475 petition when no trustworthy agent remains.

The challenger carries the burden of proof

A signed, dated, notarized power of attorney arrives in court with a presumption of validity. The challenger must prove incapacity at signing, fraud, forgery, or undue influence — suspicion about the agent's character is not evidence about the document. Expect the fight to turn on medical records near the signing date, testimony from the drafting attorney and the notary, and witnesses who saw the principal's condition day to day.

Timing matters for a second reason. Third parties — banks, buyers, brokerages — may rely in good faith on a facially valid power of attorney, and the statute binds the principal to authorized acts even after incapacity. The longer an abusive agent operates, the more assets move and the harder recovery becomes. Families who act at the first unexplained transfer fare far better than families who wait.

Revocation is the principal's own reset button

If you signed a durable power of attorney and still have capacity, you hold the fastest remedy of all. You can revoke it. Do it in writing, sign and date the revocation, and deliver it to the agent. Then notify every institution that holds the old document — your bank, your brokerage, your insurance company — because an agent who keeps a copy can keep acting until the third party learns of the revocation. If the power of attorney was used for real estate or recorded, record the revocation as well.

Most people who revoke also sign a new power of attorney naming someone they trust more, often with tighter limits: no gift authority, two agents who must act together, or a springing clause that delays effectiveness until a physician certifies incapacity. A lawyer can match those choices to your situation; our estate planning practice handles them routinely. And if you are weighing how a power of attorney fits with the rest of your plan, our guide to the disadvantages of a will covers the companion documents.

What to do next if you suspect abuse

Every family's situation is different, but the sequence that protects a vulnerable Missourian is usually the same:

Gather the power of attorney, bank statements, deeds, and any letters or texts involving the agent.
Write down what you have observed, with dates — missing funds, new names on accounts, isolation of the principal.
Consult an attorney about demanding an accounting and petitioning the probate division under RSMo 404.727.
Report suspected financial exploitation to Missouri's Adult Protective Services hotline.
Ask the court to remove the agent and, if needed, to appoint a guardian or conservator.

Move quickly. Assets transferred to third parties are harder to recover than assets still in the agent's hands, and the statute of limitations can bar claims a family sits on too long.

This guide is for informational purposes only and is not legal advice. Reading it does not create an attorney-client relationship, and the right steps depend on facts this article cannot know. If you need to challenge a power of attorney — or defend one — contact Ott Law Firm at (314) 710-2740 or through our contact page. We represent principals, families, and agents across Missouri in exactly these disputes.

Frequently asked questions

Can I revoke my durable power of attorney at any time?

Yes, as long as you still have the capacity to understand what you are doing. Revoke in writing, tell the agent, and notify every bank and institution that received a copy. If your capacity is in dispute, a court may need to resolve that question before the revocation takes effect.

Does a power of attorney become invalid when the principal dies?

Yes. Every power of attorney, durable or not, ends at the principal's death. After death, authority over the principal's property passes to the personal representative of the estate. Misconduct the agent committed before death can still be pursued — the estate or interested family members can demand an accounting and sue to recover what was taken.

Can a bank refuse to honor a valid power of attorney?

Banks and other institutions sometimes hesitate, especially when a document is old or unfamiliar. Missouri law does not require recording for the document to bind third parties, and a court can confirm an agent's authority under RSMo 404.727 when a standoff persists. An attorney's letter citing the statute resolves most refusals; a probate petition resolves the rest.

Is a power of attorney invalid if it conflicts with a will or trust?

No. A power of attorney governs affairs during your life; a will controls your estate after death, and a trust controls the property you placed in it. The documents can point in different directions without either one being invalid. If an agent used the power of attorney to move assets away from your intended heirs, the remedy is a fiduciary claim against the agent, not a declaration that the document conflicts and fails.

Can a durable power of attorney be invalidated?