Below is a good article by a Missouri attorney, J. Kirk Rahm, pertaining to how to challenge a Will in Missouri. It’s a good read and provides the basic logistics.
Will contests are brought by an heir who has been left out of a will or by an heir who is left less inheritance under a will than the heir would be entitled to receive if there had not been a will.
The time limit to contest a will in Missouri is within six months “after the date of the probate or rejection thereof by the probate division . . . or within six months after the first publication of notice granting of letters on the estate of the decedent, whichever is later . . . .” Mo. Rev. Stat. § 473.083.
If a will contest is filed, it is ordinarily necessary for everyone who has any potential interest in the estate to be served within 90 days after the will contest is filed, although additional time may be allowed under special and limited circumstances if there has been consistent and significant diligence in requesting service of the papers.
In a Missouri will contest, the jury first determines whether or not the decedent actually signed the will and declared it to be his or her will. Second, the jury determines whether or not the decedent was of “sound and disposing mind and memory.” Third, the jury determines whether the will was witnessed by at least two witnesses at the request of the decedent, in the presence of the decedent.
In determining whether the decedent was of “sound and disposing mind and memory,” the jury is instructed by the court to determine whether the decedent was able to understand the ordinary affairs of life, able to understand the extent of his or her property; “able to know the persons who were the natural objects of his bounty;” and capable of intelligently weighing and appreciating his or her natural obligations to those persons.
Assuming that the will was created and signed with the necessary formality, and that the jury determines the decedent was of “sound and disposing mind and memory,” then the usual remaining issue is whether there was such undue influence on the decedent as to cause the jury to conclude that the free will of the decedent was overpowered and destroyed, resulting in the decedent signing a will that otherwise would not have been signed.
If a will is successfully contested, then the decedent’s estate is distributed as if there had been no will. Because of this “all or nothing” aspect to will contests, there is a strong financial incentive for settlement and settlement agreements are frequently reached in will contests so that the uncertainty and risk of a trial can be avoided.
The original location for this article is: http://www.avvo.com/legal-guides/ugc/missouri-will-contest—basic-rules
In addition to Mr. Rahm’s cogent summary, I would also like to add that there are such things as “in terrorem” clauses in Missouri. An in terrorem clauses is a provision in a Will which usually says that any heir or potential beneficiary who challenges this Will loses his/her share under the Will. Essentially, it is the testator (i.e., the author of the will) saying that certain people will be disinherited if they challenge the Will. These are usually done to make things go more smoothly and avoid protracted litigation over an estate.
Consequently, be aware that some individuals have such provisions in their Wills in Missouri, and it may be best to search for such a clause before challenging a Will.