Missouri Will Requirements: How to Write a Legally Valid Will

A Missouri will that fails even one statutory requirement is void — your assets pass through intestacy as if you never wrote it. The rules under RSMo Section 474.320 are straightforward, but the details trip up more families than you'd expect.

Here's exactly what Missouri law requires, what disqualifies a will, and how to make yours self-proving so probate moves faster.

What Makes a Will Legally Valid in Missouri

Missouri requires four elements under RSMo Section 474.320:

1. Written document. Missouri does not recognize oral wills, video wills, or audio recordings. The will must be readable as text — either on paper or, as of August 28, 2025, in electronic form under RSMo Section 474.548.

2. Testator qualifications. You must be at least 18 years old (or an emancipated minor) and of "sound mind" — meaning you understand what property you own, who your natural heirs are, and what the document does.

3. Testator's signature. You must sign the will yourself, or direct another person to sign it in your physical presence. A mark or "X" is acceptable if you cannot write.

4. Two competent witnesses. At least two adults must watch you sign (or acknowledge your signature) and then sign the document themselves. Witnesses do not need to read the will's contents — they only attest that you signed voluntarily and appeared of sound mind.

The Interested Witness Trap

Missouri allows a beneficiary to serve as a witness, but it creates risk. Under RSMo Section 474.330, if a witness is also a beneficiary, they may forfeit any inheritance exceeding what they would have received under intestacy. This effectively penalizes beneficiary-witnesses — always use disinterested witnesses who inherit nothing under the will.

How to Make a Missouri Will Self-Proving

A self-proving affidavit under RSMo Section 474.337 eliminates the need for witnesses to appear in court during probate. Without it, the probate court must locate your witnesses and take their testimony — which can delay proceedings by weeks or months if witnesses have moved or died.

The process: After you and your witnesses sign the will, all three of you sign a sworn affidavit before a notary public. The affidavit uses the statutory language from Section 474.337 and states under oath that the testator was of sound mind and signed voluntarily.

The result: The court accepts the will as properly executed without requiring live witness testimony. This is the single most effective step you can take to speed up probate.

Missouri Electronic Wills (New Law — August 2025)

Effective August 28, 2025, Missouri permits electronic wills under RSMo Section 474.548. An electronic will must be:

• Readable as text on a screen or when printed
• Signed electronically by the testator
• Witnessed electronically by two adults

If no self-proving affidavit is executed at the same time, the witnesses must be physically located in a U.S. state when they witness the signing. This prevents fully remote international witnessing without the affidavit safeguard.

Common Mistakes That Invalidate a Missouri Will

Handwritten (holographic) wills without witnesses. Missouri does not recognize holographic wills. A handwritten will without two witnesses is invalid — even if entirely in your handwriting and clearly expressing your wishes.

Only one witness. Two witnesses are required. A will with only one witness signature fails the statutory test entirely.

Failing to update after major life events. A divorce automatically revokes all provisions benefiting the former spouse under RSMo Section 474.420. But remarriage, births, and property acquisitions don't trigger automatic updates — your will must be manually revised.

Naming a minor as executor. Missouri requires a personal representative to be at least 18. Naming a minor creates a vacancy that the court fills with someone you may not have chosen.

What Happens Without a Valid Will

If your will fails any requirement, Missouri treats you as intestate under RSMo Section 474.010. The distribution formula is rigid:

• Spouse, no children: Spouse gets 100%
• Spouse + shared children: Spouse gets the first $20,000 plus 50% of the balance; children split the rest
• Spouse + children from a prior relationship: Spouse gets 50%; children split 50%
• No spouse: Children inherit equally

Stepchildren inherit nothing. Unmarried partners inherit nothing. Charities you care about get nothing. The intestacy formula cannot be adjusted for family circumstances — which is precisely why a valid will matters.

Missouri Will Requirements Checklist

Use this as your execution checklist:

1. Draft the will in writing (typed or electronic)
2. Confirm the testator is 18+ and of sound mind
3. Gather two disinterested adult witnesses (non-beneficiaries)
4. The testator signs in the presence of both witnesses
5. Both witnesses sign immediately after
6. Execute the self-proving affidavit before a notary (all three sign under oath)
7. Store the original in a secure location and inform your personal representative

The Missouri Basic Estate Planning Kit includes step-by-step instructions for writing a Missouri-compliant will, executing the self-proving affidavit, and coordinating your will with beneficiary deeds and POD/TOD designations to keep your estate out of probate entirely.

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