A will is valid when the person signing it is a legal adult of sound mind, the document is in writing, the testator signs it, and the signing is witnessed according to state rules. That is the short version of what makes a will valid, and nearly every state agrees on those bones. The differences — and the mistakes that quietly void otherwise careful documents — live in the details: where the signature goes, who may witness, whether a handwritten page counts, and what happens after the pen is capped.
Who Can Make a Will
You must be at least 18 to make a will in nearly every state. The Uniform Probate Code, adopted in whole or in part by most states, sets that floor. A few states carve out exceptions for people under 18 who are legally emancipated, currently married, or serving in the military. Outside those narrow situations, a will signed by a minor is invalid no matter how carefully it was drafted.
Mental capacity is a separate question and the one that trips people up. Courts apply a test called “testamentary capacity” or “sound mind,” which asks whether, at the moment of signing, the testator understood four things: the nature and extent of their property, who their natural heirs are (spouse, children, other close relatives), what the will does with that property, and how those pieces fit together into a coherent plan. The last element matters most. Someone who can list their assets but cannot connect ownership to distribution has not cleared the bar.
The threshold is lower than most people assume. Early-stage dementia, occasional confusion, or dependence on others for daily tasks does not automatically disqualify someone. Capacity is judged at the specific moment of signing, which is why a lucid interval can support a valid will even when general health is poor. Courts weigh medical records, witness testimony, and the observations of any attorney who supervised execution. Heavy sedation, active psychosis, or an inability to recognize close family at the time of signing gives challengers their strongest footing.
Writing and Signature
Almost every state requires a will to be in writing. Typed or printed documents are the standard. A physical document can be authenticated, stored, and examined in ways a verbal statement cannot, which is why oral wills are so narrowly accepted.
You must sign the document personally. If a physical disability prevents you from signing, most states allow another person to sign on your behalf, but only at your explicit direction and in your presence. A guided signature, where someone steadies the testator’s hand, generally satisfies the requirement so long as the testator directed the act and acknowledged the result.
A minority of states follow a subscription rule, which requires the signature to appear at the very end of the document. The logic is that nothing can be added below a signature that comes last. In those states, text appearing below the signature is typically disregarded, and a misplaced signature can invalidate the whole will. Most states following the Uniform Probate Code are more flexible, allowing the signature anywhere on the document as long as the testator intended it to authenticate the will.
Witnesses
All but a few states require at least two witnesses to the signing. Witnesses do not need to read the will or know its contents. They need to watch the testator sign, or hear the testator acknowledge a signature already on the document, and then sign the will themselves. That layered process creates independent verification that the right person signed voluntarily and appeared competent.
How close the witnesses must be depends on state law. Line-of-sight states require that the testator and witnesses be positioned where they can actually see each other sign without obstruction; stepping into another room breaks the chain. Conscious-presence states only require that the testator be aware the witness is in the act of signing, whether through sight, hearing, or general awareness. The Uniform Probate Code uses the conscious-presence approach.
The Interested-Witness Problem
An interested witness is one who stands to inherit under the will they are witnessing. States handle this very differently. Some follow the Uniform Probate Code and let the witness keep the inheritance with the will fully intact. Others apply a purging rule that strips the witness of all or part of the gift, sometimes allowing the witness to keep only what intestacy or a prior will would have given them. A few states presume the gift is the product of undue influence and let the witness fight to keep it. The safe practice everywhere is simple: do not use anyone named in the will as a witness.
Self-Proving Affidavits
A self-proving affidavit is a notarized statement attached to the will in which the testator and witnesses swear under oath that execution was done properly. The testator confirms signing voluntarily, being of legal age, and acting under no constraint. The witnesses confirm observing the signing and that the testator appeared mentally competent. A notary certifies the signatures and seals the document.
The payoff comes during probate. Without the affidavit, the court may need to locate the original witnesses to confirm the will was properly executed, which becomes difficult or impossible as years pass. A self-proved will can typically be admitted without any witness testimony. It does not protect against challenges on other grounds, but it removes execution formalities as an obstacle.
Errors in the affidavit — a wrong date, a notary acting outside their commission, a missing signature — can strip the self-proving status. The underlying will usually survives, but the court falls back to requiring witness testimony. The cost of skipping or botching the affidavit shows up years later, when it is too late to fix.
Handwritten, Oral, and Electronic Wills
Roughly half of states recognize holographic wills, which are written entirely in the testator’s own handwriting and typically require no witnesses. To qualify, the document must be in the testator’s hand (typed or printed text does not work) and must clearly express testamentary intent, meaning it is meant to distribute property at death rather than record wishes or write a letter. The testator must sign it. Most states accepting holographic wills do not require the signature in any particular place and do not require a date. Probate usually requires sworn testimony from people familiar with the testator’s handwriting unless the holographic will was also made self-proving. The practical weakness of holographic wills is ambiguity: without careful drafting, the language often creates the disputes a will is supposed to prevent.
Oral wills, sometimes called nuncupative wills, are invalid in most states. Where recognized, they are usually limited to military personnel on active duty during armed conflict or mariners at sea, and sometimes extended to anyone in imminent peril of death. Even then the declaration generally must be made in front of at least two witnesses, the value or scope that can pass is often capped, and the will typically expires once the emergency passes. An oral will is not a long-term estate plan.
A growing number of states permit wills to be created, signed, and witnessed electronically, with several enacting laws based on the Uniform Electronic Wills Act or their own statutes. Most states still require a traditional paper document with wet-ink signatures. Where electronic wills are allowed, the requirements generally mirror those for paper: an electronic signature by the testator, witness observation, and a notarial act. Some states allow the entire process to run remotely over audiovisual technology; others require physical presence for at least some participants. Remote execution often carries extra safeguards, such as attorney supervision and on-camera identity and location confirmation. A will that is valid where it was signed may face challenges in a state that has not adopted electronic will legislation, so verify your state’s current rules before relying on this route.
Undue Influence and Other Attacks
A will can be thrown out even when the testator was technically competent, if someone else manipulated the decision. Undue influence claims do not require proof of incapacity. They focus on whether another person applied enough pressure that the will reflects that person’s wishes instead of the testator’s.
Direct proof almost never exists, so courts rely on circumstantial evidence. Red flags include a testator who was vulnerable due to age, illness, or emotional distress; an alleged influencer who controlled the testator’s housing, finances, or medical access; and a disposition that would surprise a reasonable observer. A parent who suddenly disinherits all of their children in favor of a recently hired caregiver invites scrutiny that a more predictable plan would not.
In many states, a rebuttable presumption of undue influence arises when three conditions line up: a fiduciary or confidential relationship between the testator and the beneficiary, the opportunity to influence the testator’s decisions, and substantial benefit to that person under the will. Once a challenger establishes those elements, the burden shifts to the beneficiary to prove the will was genuine. When an attorney or financial advisor helped draft a will that benefits them personally, the presumption is especially hard to overcome.
Keeping the Will Valid Over Time
A will is not permanent. You can revoke it two ways: by executing a new will that expressly revokes the old one (or is so inconsistent with it that both cannot stand), or by physically destroying the document with intent to revoke. Burning, tearing, canceling, and obliterating all count in most states. Intent matters. Shredding a will accidentally does not revoke it, and tearing up a photocopy while the original sits in your attorney’s office accomplishes nothing. Someone else can destroy the will for you, but only in your presence and at your explicit direction.
If a new will makes a complete disposition of your estate, courts presume you meant it to replace the old one. If the new will covers only part of your property, it is presumed to supplement rather than replace, revoking only the provisions that directly conflict.
Divorce
In most states, divorce automatically revokes any provision benefiting your former spouse. Property that would have gone to the ex passes as though the ex died before you, and any appointment of the ex as executor, trustee, or guardian is similarly void. Remarrying the same person revives those provisions. A legal separation that does not end the marriage does not trigger automatic revocation, which catches many people off guard. Outside of divorce, no change in life circumstance automatically revokes a will under this model.
Codicils
A codicil is an amendment to an existing will. It must be executed with the same formalities as the original, meaning signed, witnessed, and ideally notarized with a self-proving affidavit. Codicils work for small, isolated changes like swapping an executor or adjusting a single bequest. For anything more complex, drafting a new will is cleaner. A codicil that conflicts with the original in ambiguous ways creates exactly the kind of interpretive puzzle that leads to litigation.
Store the Original Where Your Executor Can Find It
Probate courts almost universally require the original will. Not a photocopy, not a scan, not a notarized reproduction. When the original cannot be found, most states presume the testator destroyed it intentionally, and the estate is treated as intestate. Overcoming that presumption requires producing a copy along with evidence that revocation was never intended, and typically all heirs must be notified and allowed to object. It is a difficult and expensive process to avoid.
Common storage options include a fireproof home safe, a safe deposit box, the drafting attorney’s office, or filing with the local probate court, which many jurisdictions allow for a nominal fee. Each option has trade-offs. A safe deposit box can be hard for an executor to access after death. An attorney may retire or relocate. A home safe may not survive a fire. Whatever you choose, make sure your executor knows where the original is and can reach it without a court order. A perfectly drafted will that nobody can find is functionally the same as no will at all.