Dying without a will may be the ultimate example of leaving unfinished business.

Deciding who gets what--and arranging it so lawyers and Uncle Sam don't take too much--is just smart planning. Yet more than half of American adults die without wills, leaving heirs confused as well as grieving. Fortunately, heirs have ways to ensure they get their share of a legacy.

When someone dies intestate, or without a valid will, state laws determine how the property is carved up. The rules vary widely. In some states, spouses get half of everything not jointly owned, with the rest split evenly among surviving children. In others, the spouse may get as little as one-third. Unmarried partners are out of luck. "There's nothing in the typical intestacy laws that provides for what legally are just friends," says San Francisco lawyer Myron Sugarman.

EARLY STEPS. For survivors, step No. 1 is to hire a lawyer. An attorney can help appoint an administrator or personal representative, who can be a person close to the family or a lawyer or accountant. It's wise to do this early on. Although four surviving brothers may want the post, "four people running an estate can be chaos," says Pennsylvania lawyer Michael R. Schwartz.

Beyond paperwork, many decisions are out of the administrator's hands. State-mandated inheritance hierarchies come into play. First comes the spouse, who would take his or her share plus a mandatory allowance provided in some states. In Pennsylvania, the spouse gets the first $30,000 on top of a 50% share. Then come the kids, who split the rest evenly. There are wrinkles: A second spouse may not get the allowance even though the first marriage ended legally. In California, spouses get all the so-called community property--assets they acquired while married--which could freeze out all other relatives.

Generally, the law favors spouses. No federal estate tax is levied on the spouse's inheritance. But anything that goes to other heirs is taxed. Rates start at 37% after the first $650,000 and rise to 55%. Of course, when an asset is jointly owned, most states will let it pass without tax to the surviving partner.

State law also sets who the eligible heirs are. In Pennsylvania, first cousins once-removed are the most distant kin entitled to a piece of the pie. And it's your bad luck if your rich, late aunt lived in New Hampshire, says Harvard Law School professor David Westfall. There, a relative beyond a spouse or direct descendant can inherit, but must pay an additional 15% tax on top of the federal levy.

When no eligible heirs step forward, the windfall generally goes to state or local authorities. States often try to find heirs by running newspaper ads but may not go beyond that. Some put a limit on how long an estate can go unclaimed; others will let it sit for years. New Jersey may move on the money in a few months. Genealogical tracing services may ferret out long-lost kin--and then bargain with them for up to a one-third share of the estate. They often won't name the estate they're working on until the heirs come to terms with them. If you get a call from a bounty hunter, haggle. After all, these lineage sleuths get nothing if you won't play.

Once potential heirs are lined up, the next challenge is taxes. Along with the federal levy, some states add their own tax. But others, including geriatric-friendly states like Florida, don't. And there are ways to limit some taxes. One common tactic: Skip a generation. When a parent dies, an adult child may disclaim his cut and let it pass to his children. That way, he avoids double taxation--once when he inherits, and the second time when his kids do. One caution: Large estates can be subject to an additional generation-skipping tax.

A will is the best way to leave a legacy. Without a valid will, heirs have little room to maneuver. But they can at least make sure they get what they're entitled to.

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