"I'm not the first president to call for this idea that everybody has got to do their fair share. Some years ago, one of my predecessors traveled across the country pushing for the same concept. He gave a speech where he talked about a letter he had received from a wealthy executive who paid lower tax rates than his secretary, and wanted to come to Washington and tell Congress why that was wrong. So this president gave another speech where he said it was 'crazy' -- that's a quote -- that certain tax loopholes make it possible for multimillionaires to pay nothing, while a bus driver was paying 10 percent of his salary. That wild-eyed, socialist, tax-hiking class warrior was Ronald Reagan.
"He thought that, in America, the wealthiest should pay their fair share, and he said so. I know that position might disqualify him from the Republican primaries these days but what Ronald Reagan was calling for then is the same thing that we're calling for now: a return to basic fairness and responsibility; everybody doing their part. And if it will help convince folks in Congress to make the right choice, we could call it the Reagan Rule instead of the Buffett Rule." President Obama on the Buffett Rule
And here's a handy-dandy Buffett Rule calculator provided by the White House.