Greg Mankiw calculates his marginal tax rate as 80%. Two years ago, he estimated that his marginal tax rate under an Obama administration would be 93%. (1-0.80)/(1-0.93)=2.9, so . . . Mankiw is actually keeping 290% of the amount of money he was expecting to keep.
P.S. I wasn’t really following the details of Mankiw’s calculation. Given the dramatic change in only two years, I assume his numbers must depend on some highly time-sensitive parameters.