You must show "standing" in order to challenge a will in court. "Standing" means that you can show that you would be affected by the outcome of the legal proceeding. Only interested parties have standing to challenge wills. An interested party includes a person named as a beneficiary who believes that the property should have been distributed differently. A person not named in the will but who reasonably could expect to have inherited, such as a child or sibling, is also an interested party.
Claim Legal Grounds
Once you have established standing, you must base your claim on legal grounds. Some common grounds for challenging a will include the validity of the will itself, the testator’s mental capacity at the time of writing the will, fraud and undue influence. Just because you had hoped to receive a larger inheritance does not constitute legal grounds to challenge a will if other legal grounds do not exist.
The court will require you to show proof of the grounds you claim. If you claim that the testator was not of sound mind, you might present medical records, psychiatric evaluations or witnesses to the testator’s diminished capacity. If claiming undue influence, you might present evidence of predisposing factors -- such as the testator's depression or dementia -- and the nature of the relationship between the testator and the person you believe has unduly influenced the testator. A forgery claim might include a handwriting expert to testify that the signature on the document is not the testator’s.
Spouses are in a unique position. All states have estate laws that provide certain legal rights to spouses. Even if you were to leave your spouse out of the will, intentionally or not, the law may supersede your will in some cases. A spouse can challenge the will regardless of its validity in cases where a spouse has been fully or partially disinherited. However, the voluntary waiver of a spouse through a prenuptial agreement, or the creation by the testator of non-probate estate assets, can result in partial disinheritance. A court can rule on issues regarding the validity of a prenuptial agreement or the legality of the transactions establishing non-probate estate assets.
Every state has its own procedural rules regarding how to challenge a will, but generally, you must challenge the will during probate and meet the deadline established by your state for filing the challenge.