A will is legally invalid when it fails one of the rules that gives it force: it wasn’t signed and witnessed the way the state requires, the person signing didn’t have the mental capacity to make it, someone pressured or tricked them into it, or the will was later revoked by a new document, by destruction, or by operation of law after a divorce. When any of those defects is proven, a court can throw out the whole document or just the tainted parts, and the estate then passes under an earlier valid will or under the state’s default inheritance rules.
Signing and Witness Defects
Most successful challenges start here, because the formal rules are objective and easy to check against the document itself.
The person making the will generally must be at least 18. Some states carve out exceptions for emancipated minors or active-duty military, but the age floor applies in the vast majority of jurisdictions.1Legal Information Institute. Testamentary Capacity The will must also be in writing—typed, printed, or handwritten—in some reasonably permanent form.2Legal Information Institute. Wills Writing Requirement It must be signed by the testator, or by someone else in the testator’s presence and at the testator’s direction. Courts take a broad view of what counts as a signature; a first name, a nickname, or an “X” from someone who cannot write can qualify if the person intended it as a signature.
Under the Uniform Probate Code, which many states have adopted in some form, at least two witnesses must sign the will. Each witness must have seen the testator sign or heard the testator acknowledge the signature. A will missing the required witness signatures is typically invalid on its face, and that is one of the easiest grounds to raise in probate court.
A related trap: when a witness is also named as a beneficiary. In many states the will itself stays valid, but the gift to that witness is voided unless enough other disinterested witnesses were present. The reasoning is that someone who stands to inherit is not a reliable witness to the signing.
Handwritten and Electronic Wills
A holographic will—handwritten and signed by the testator without witnesses—is recognized in only some states, and the rules vary.3Legal Information Institute. Wex Definition – Holographic Will Some require the entire document to be in the testator’s handwriting; others require only that the material portions disposing of property be handwritten. A document that is valid in one state may be worthless in another, and courts scrutinize these wills closely because there is no witness testimony to back them up.
Purely electronic wills sit in similar uncertainty. As of 2022, roughly ten states explicitly allowed them, four follow the Uniform Electronic Wills Act, two expressly ban them, and the rest leave the legal status unclear. A court in a state without an authorizing statute can refuse to recognize an electronic will at all.
Lack of Testamentary Capacity
Even a perfectly signed will fails if the person who signed it didn’t have the mental ability to make it. The standard, called testamentary capacity, is lower than most people assume. At the moment of signing, the testator must be able to:1Legal Information Institute. Testamentary Capacity
- Know in general terms what they own.
- Identify the people who would naturally expect to inherit, such as a spouse, children, or close relatives.
- Understand that a will controls who receives their property at death.
- Form a coherent plan connecting the property to the chosen recipients.
A diagnosis of dementia or mental illness does not by itself disqualify someone. Courts have upheld wills signed by people with Alzheimer’s disease where testimony from the drafting attorney, the witnesses, or family members showed the testator was coherent when signing. The idea of a “lucid interval” in progressive dementia is increasingly questioned by medical experts, and a will signed in advanced dementia faces steep odds in a contest. Doctors’ opinions carry weight, but firsthand accounts from people in the room often weigh as much or more.
Insane Delusions
A separate ground is the “insane delusion”—a false belief with no basis in reality that the testator holds against all evidence. Someone can pass every capacity test and still carry a specific irrational belief, such as the conviction that a loyal child is secretly plotting against them, that shapes who they include or exclude. If a challenger can show the delusion actually drove particular provisions, a court can strike those provisions and leave the rest of the will intact. The question is whether the delusion affected the terms, not whether the testator held odd beliefs generally.
Undue Influence, Fraud, and Duress
A will must reflect the testator’s own wishes. Courts invalidate wills, or specific gifts within them, when someone else improperly controlled the process.
Undue influence happens when a person in a position of trust substitutes their wishes for the testator’s. The classic pattern involves an aging parent and an adult child who controls access to the parent, cuts off other relatives, and steers the parent toward a new will heavily favoring the child. Courts examine whether a confidential relationship existed, whether the influencer had the opportunity to apply pressure, and whether the terms are suspiciously favorable to the person with that access.4Legal Information Institute. Undue Influence
In many states, once a confidential or fiduciary relationship is proven, the burden of proof shifts. The beneficiary accused of influence must then prove the will reflected the testator’s genuine intent, rather than the challenger having to prove it didn’t. That shift matters in practice because direct evidence of private manipulation is scarce; most of it happens behind closed doors.
Fraud involves tricking the testator into signing or into including specific terms. Examples range from forging a signature, to telling the testator the document is a power of attorney rather than a will, to lying about a family member’s conduct to turn the testator against them. Duress involves threats or coercion—intimidation, physical restraint, or psychological pressure that forces the signature. Either can void the whole will or only the tainted provisions, depending on how deeply the misconduct infected the document.
Revocation After Signing
A will that was valid when signed can lose its force later. There are three main routes, and one of them catches people off guard.
A New Will or Codicil
The cleanest way to revoke a will is to execute a new one that expressly revokes all prior wills. A new will can also impliedly revoke an older one by making a complete plan for the entire estate, which signals an intent to replace it. A codicil amends specific provisions without replacing the whole document. Either way, the new instrument must satisfy the same formal requirements as the original.5Legal Information Institute. Revocation of Will by Act
Physical Destruction
A testator can revoke a will by tearing it, burning it, or writing “VOID” across it. Two elements must line up: the physical act and the intent to revoke. Shredding a will by accident while cleaning out files doesn’t count. Neither does destruction by someone else without the testator’s knowledge or direction. If another person destroys the will at the testator’s request, they typically must do so in the testator’s presence.5Legal Information Institute. Revocation of Will by Act
Divorce
More than 40 states have statutes that automatically revoke will provisions benefiting a former spouse once a divorce is final. In about 26 of those states, the revocation reaches beyond wills to beneficiary designations on insurance policies, bank accounts, and other financial instruments. The effect is as if the ex-spouse had died first, and the share passes under the remainder of the will or under state law. These statutes generally do not reach retirement accounts governed by federal law, such as 401(k) plans, where a pre-divorce beneficiary designation stays in effect until it is affirmatively changed. The safe move after any divorce is a new will and a fresh pass through every beneficiary designation.
Lost or Missing Wills
If an original will was known to exist but cannot be found after the testator’s death, courts in most states presume the testator destroyed it with the intent to revoke. Anyone trying to probate a copy or prove the lost will’s contents faces a heavy burden, usually clear and convincing evidence that the testator did not revoke it. Proof might include showing that an attorney held the original, or that the will was stored somewhere the testator didn’t control. Without enough to overcome the presumption, the will is treated as revoked.
Partial Invalidity
A defect doesn’t always take down the whole will. Courts regularly invalidate specific provisions while leaving the rest intact. Undue influence that tainted one bequest, a gift to a witness who should have stayed disinterested, or a provision driven by an insane delusion can be struck on its own, with the remaining valid terms controlling the rest of the estate. Which defect you can prove shapes how much of the document falls.
What Happens if a Will Is Thrown Out
When a court invalidates a will, the estate doesn’t sit in limbo. There’s an order of succession for what controls next.
If the invalid will revoked an earlier valid will, that earlier document may be revived and used to distribute the estate. Whether revival happens automatically depends on state law—some states revive the prior will, others require evidence that the testator intended revival.
If no earlier valid will exists, the estate passes under the state’s intestacy rules.6Legal Information Institute. Intestate Succession Those rules distribute property in a fixed order, usually starting with a spouse and children and moving outward to parents, siblings, and more distant relatives. They don’t account for estrangements, close non-family relationships, or anything the testator actually wanted. An unmarried partner, a close friend, or a charity the testator meant to support will receive nothing under intestacy, regardless of their place in the testator’s life.
Who Can Raise These Grounds
None of these grounds matter unless someone with legal standing brings them to court. Standing generally comes down to a direct financial stake in the outcome, and two groups usually qualify:
- Beneficiaries named in the will who believe a defect affected specific provisions.
- Heirs who would inherit under state intestacy rules if the will were thrown out—typically a spouse, child, parent, or sibling who was reduced or cut out.
Creditors and others with claims against the estate may have standing in some jurisdictions, but most contests come from family members or named beneficiaries. Filing deadlines vary by state, with windows commonly running from a few months to a couple of years after the will is admitted to probate. Miss that window and the grounds no longer matter, however strong they are.