Estate taxes are levied on the total current value of all of the junk you leave behind. Anything you leave to a nonprofit organization or to your spouse is exempt, and there are additional rules to protect family businesses, farms, and the like.
Digging back through seventy years of Congressional tax reform records (1), I was able to reconstruct the historical estate tax rates, brackets, and exemptions back through 1942 (2). I used a dizzying array of spreadsheet functions to correct for inflation and generate this graphic of historical effective tax rates:
|US historical estate tax rates. y-axis is year (2013 on top); x-axis is estate size ($0-127,000,000); each color is 8%|
The top estate tax rate from 1947-1976 was 77%; the top rate dropped to 55% for most of the 1980's and 1990's and now sits at 40%. Meanwhile, the inflation-adjusted estate tax exemption limit - the estate size on which no taxes are paid - has risen substantially: