It usually requires a pretty significant event to disqualify a beneficiary from inheriting under the terms of a last will and testament. This isn't to say that it doesn't happen, however, or that it happens infrequently. A few common circumstances -- and some that aren't so common -- can prevent one or more of your intended beneficiaries from accepting the gifts you left to them.
Divorce and Separation
It shouldn't come as much of a surprise that if you break up with your spouse, she may not be entitled to inherit from you. This is a safeguard in place in most states to prevent her from benefitting if your divorce or legal separation is final and you die before you have a chance to make a new will. Two exceptions exist to this rule, however. If you do amend your will after your divorce, you can state unequivocally that you want her to inherit regardless of the fact that your marriage went south -- and the courts in most states will honor this. Additionally, if you remarry that person, your second wedding reinstates her inheritance rights.
Leaving Bequests to a Caregiver
Some states, such as California, will not allow a caregiver to inherit from you if she tended to you in the last months of your life. This rule is in place to prevent unscrupulous individuals from taking advantage of you when you're physically incapacitated and perhaps at their mercy. A caregiver might coerce, threaten or sweet talk you into changing the terms of your will to leave her a substantial gift. Disqualified caregivers typically include physicians, nurses and the staff at a nursing home, a paid companion who cares for you at home, or even a friend who spends a lot of time taking care of you in your final days. Some courts may make an exception if you were friends for many years before you grew ill or infirm. This rule typically does not apply to relatives.
Witnesses and Executors
Witnesses to your will and the executor named in the document can usually be beneficiaries, but specific requirements are dependent on state law. For example, in Tennessee, your witness who is also a beneficiary is not disqualified from taking a legacy under your will if you add two disinterested persons as witnesses as well. If you don't add these witnesses, it's possible that your beneficiary might inherit anyway if she's related to you. She would still be entitled to a share of your estate equal to what she would have received if you had died without a will. The law isn't typically as strict with executors. If there's a conflict after your death between your executor's responsibilities to your estate and the inheritance she is to receive, she wouldn't necessarily be disqualified from inheriting, but she may have to step down as executor.
If your death is the result of murder or manslaughter, the perpetrator is usually disqualified from inheriting from you. Some states make a distinction between different levels of conviction, however. For example, in New York, your beneficiary can inherit if you died at her hands due to negligent homicide, but not if your death was the result of murder or first or second degree manslaughter.