In property law, a life in being is a specific human person who is alive at the moment a future property interest is created and whose lifespan is used to measure whether that interest will become final in time. The concept comes from the Rule Against Perpetuities, which, as John Chipman Gray stated it, requires that no interest is good unless it must vest, if at all, not later than 21 years after some life in being at the creation of the interest.1Legal Information Institute. Rule Against Perpetuities That person’s death starts a 21-year countdown. If the interest might still be hanging in the balance when the countdown ends, the traditional rule treats the gift as void from the start.
Who Qualifies as a Life in Being
A life in being has to be a natural, identifiable human being alive at the exact moment the future interest is created.1Legal Information Institute. Rule Against Perpetuities The person doesn’t have to be named in the document, and they don’t have to be a beneficiary. What matters is that their life or death has a logical connection to whether and when the interest will vest, and that the date of their death can be verified.
Someone who is already dead when the interest is created cannot serve. Neither can someone not yet conceived. Only people whose lives overlap, even by a single day, with the moment of creation count.
A life in being can also be a class of people rather than one individual, but only if the class is closed when the interest is created — no new members can join afterward.1Legal Information Institute. Rule Against Perpetuities A gift “to my grandchildren living at the time of my death” closes the class at death, and each grandchild then alive can anchor the calculation. A gift “to all my future grandchildren” leaves the class open and creates the uncertainty the rule was meant to shut down.
Non-humans are excluded. Corporations, LLCs, charities, and other legal entities don’t qualify, because they can exist indefinitely and have no death event to trigger the countdown. Animals don’t qualify either. Pet trusts exist in most states, but they operate under separate statutes that cap the trust at the animal’s lifetime or 21 years rather than treating the animal as a measuring life.
When the Perpetuities Clock Starts
The moment the clock starts determines who counts as a life in being, so the trigger date drives everything else.
- For a will, the clock starts when the testator dies, not when the will was drafted or signed.
- For a deed, it starts when the deed is physically delivered.2Duke Law Scholarship Repository. A Practical Guide to the Rule Against Perpetuities
- For an irrevocable trust, it starts when the trust is funded.
- For a revocable trust, the clock doesn’t start until the trust becomes irrevocable, which typically happens at the grantor’s death.
Everyone alive at that triggering moment is a candidate to serve as a life in being. Everyone born later is not, with one narrow exception discussed below.
How to Identify the Measuring Life
The measuring life, sometimes called the validating life, is the specific person whose lifespan actually anchors the deadline for a given interest. Finding that person is a matter of reading the gift and asking whose death the vesting condition depends on.
Take a will that says “to my son for life, then to his children who reach age 25.” The son is the obvious measuring life. He was alive when the testator died, every child of his will be born during his lifetime, and once he dies, each surviving child has at most 21 years to reach 25. The gift works.
Now change the age to 30. The son’s children, born during his life, could still be as young as nine when he dies, and would need 21 more years plus some to hit 30. Under the traditional rule, that possibility is enough to kill the entire gift at inception.
The measuring life doesn’t have to receive anything under the document. It can be anyone whose death can be proven and whose lifespan logically relates to the vesting event. If no human can be identified or implied as a measuring life, the interest gets only the bare 21-year period, which rarely leaves enough room.
The 21-Year Add-On
After the measuring life dies, the rule allows an additional 21 years for any remaining contingencies to resolve.1Legal Information Institute. Rule Against Perpetuities The buffer exists to cover the gap between a measuring life’s death and the moment the next generation reaches adulthood. Combined with a typical lifespan, it stretches the outer limit of the perpetuities window to roughly 90 or 100 years.
If there is any possibility, however remote, that the interest could still be unvested after that combined window closes, the traditional rule voids the entire transfer from inception. The gift is not valid at creation and then invalidated later; it was never valid at all.
Children Conceived but Not Yet Born
A long-standing legal fiction treats a child conceived but not yet born at the moment of creation as a life in being, provided the child is later born alive. That child’s lifespan then functions as a measuring life just like anyone else who was already walking around.
In practice, this effectively extends the perpetuities period by the length of gestation. If a testator dies and a grandchild is born seven months later, the grandchild counts as having been a life in being at the testator’s death. The exception matters most when a testator dies with heirs on the way.
Two Classic Traps the Rule Creates
The traditional rule tests possibilities, not probabilities, which produces results that read as absurd on the facts. Two scenarios became famous enough to earn their own names, and both still appear on bar exams even though most states have reformed around them.
The Fertile Octogenarian
Common law assumed any living person could have more children regardless of age. Under this fertile octogenarian rule, an 80-year-old woman was treated as capable of bearing another child, and if that hypothetical future child could push the vesting of an interest beyond the allowed period, the whole interest failed at inception. Most states have abandoned the presumption, either by capping assumed fertility ages or by moving to a wait-and-see system.3Legal Information Institute. Fertile-Octogenarian Rule
The Unborn Widow
A gift to someone’s “widow” is read to mean whoever is married to that person at death. Because the person could theoretically marry someone not yet born when the interest was created, that future spouse is not a life in being, and any gift depending on her lifespan fails the possibilities test. A bequest “to my son for life, then to his widow for life, then to his children” is void under the strict common law rule, even if the son is already married at the time of the will.2Duke Law Scholarship Repository. A Practical Guide to the Rule Against Perpetuities
Which Future Interests the Rule Actually Reaches
Not every future interest triggers a perpetuities analysis, and knowing the boundaries prevents the concept from being applied where it doesn’t belong.
The rule targets contingent interests, where it is still uncertain whether or who will receive the property. A vested remainder, where the recipient is already identified and the right is not subject to any condition, falls outside the rule entirely.4Legal Information Institute. Vested Remainder Interests the grantor keeps for themselves — reversions, possibilities of reverter, rights of entry — are also generally exempt, because the rule concerns itself with gifts to third parties.
Charitable trusts get their own exemption when property passes from one charitable purpose to another. The exemption does not cover a shift from charitable use to a private individual; that transfer is tested like any other.
How Modern Statutes Have Changed the Picture
The traditional rule’s rigid “what might happen” test produced results harsh enough that most states have modified it. The life in being still matters in each framework below, but the consequences of getting it wrong are softer than they were a century ago.
Wait-and-See
Wait-and-see statutes skip the hypothetical analysis at creation and instead observe what actually happens. If the interest in fact vests within the perpetuities period, it is valid, regardless of whether some theoretical scenario at creation might have pushed it past the deadline. Some versions, called “second look” statutes, specifically require the validity check at the death of the life tenant.
USRAP
The Uniform Statutory Rule Against Perpetuities, or USRAP, added a flat 90-year alternative vesting period. An interest is valid if it either satisfies the common law test or actually vests within 90 years of creation. The 90-year figure was chosen to approximate a typical life-plus-21 window. Over half of U.S. states have adopted USRAP or a close variant.
Abolition for Trusts
More than two dozen states and the District of Columbia have repealed the Rule Against Perpetuities for trusts, allowing them to last indefinitely. In these jurisdictions, the life in being concept has no practical role: there is no deadline to measure against, no 21-year countdown, and no risk of the interest being voided. Dynasty trusts formed under these laws can run for centuries. Whether a given trust falls under common law, USRAP, wait-and-see, or no rule at all depends entirely on the governing state’s law, which is why the state of the trust matters as much as the drafting.
Saving Clauses
In well-drafted modern instruments, the entire life in being analysis is handled by a single provision called a saving clause. A typical saving clause says that regardless of anything else in the document, every trust created under the agreement must terminate no later than 21 years after the death of the last surviving beneficiary who was alive at the grantor’s death, with all assets distributing out immediately if that deadline is reached.
The clause works by guaranteeing on paper that no interest can possibly vest outside the allowed window, which forces the gift to pass the perpetuities test as a matter of structure rather than hope. Some clauses name specific measuring lives, occasionally people unrelated to the trust, simply to provide a verifiable set of lifespans. Others use a “shorter of” structure, limiting the trust to the shorter of its intended term or the perpetuities period.
When a document lacks a saving clause and an interest fails the rule, some states authorize courts to reform the offending provision — reducing a vesting age from 30 to 21, for example — to bring it inside the deadline while staying as close as possible to the grantor’s intent. Others apply a broader cy pres doctrine for the same purpose. Both approaches are second-best fixes; the saving clause is the first.