In 2010, after a year in which the estate tax was zeroed out altogether, Congress passed a law that set the estate tax at 35 percent and exempted all estates under $5 million, adjusted for inflation. That law expires in January 2013 when the exemption will fall to $1 million and the tax will rise to 55 percent.

Many families are faced with a stark proposition. If the life of an elderly wealthy family member extends into 2013, the tax bills will be substantially higher.