...the short answer is: some, but not enough to make a dent in the deficit. If you put a floor at their current marginal tax rate of 35%, the government would obtain $37 billion more dollars. That might sound like a lot, but it amounts to just 2.5% of the 2009 $1.5 trillion deficit (which is the red line shown). If you increase the floor to the pre-Bush-tax-cut marginal rate of 39.6%, the additional revenue grows a bit — to $66 billion, or 4.5% of the year’s deficit.
...So this Buffet Rule is a great populist proposal if the president wants to score some political points, but it has little practical value. It might provide the government a little bit of additional revenue, but unless extremely aggressive, it wouldn’t make a dent in the nation’s deficit problem. To do that, you’ll need to cut entitlements and/or raise taxes much more broadly.
Or you'll need to unleash the private sector and grow the economy.
Hat tip: NRO.