Confusion arises only if we look at part of the picture. For example, everyone who is employed pays social security tax and personal income tax. But only those with investment income pay capital gains and dividends tax. And in order for investors to receive capital gains and dividend income, the companies they have invested in—with after-tax dollars—need to pay a corporate income tax. Consider, for example (and I'm simplifying), a worst-case scenario person who is self-employed, whose income puts him in the top Federal and California income tax bracket, and who has substantial income from investments. He pays 35% federal income tax, 9% state income tax, a 15% social security tax, and a 2% medicare tax. Any income he receives from his investments—which were originally made with after-tax dollars—is effectively what the companies he owns have earned after paying a 35% corporate income tax, and on top of that he must pay 15% of what is distributed to him—he might be paying an effective tax on his total investment income of as much as 45%. Depending on how the numbers stack up, this unfortunate person could be paying an enormous effective tax rate—well over 50%—on his total income.
When Warren Buffet says he only pays a 15% effective tax on his income, that's because his income mainly comes from capital gains and dividends, and he is completely ignoring the fact that the companies he owns must pay a corporate income tax of as much as 35% before he can receive those gains and dividends.
Fortunately, we do have access to facts that do not distort or color the picture. The chart below uses the numbers as crunched by the Congressional Budget Office. The effective total tax rate shown is the ratio of total federal taxes (income, social security, corporate, excise) divided by comprehensive household income. As Greg Mankiw notes, our tax system is highly progressive: "the rich face average tax rates more than twice those of the middle class, and about seven times those of the lowest quintile." And these effective tax rates include all the benefits of whatever deductions may have been available to individuals and companies along the way.
Greg Mankiw also has a nice summary of how progressive our tax system actually is:
1. The U.S. personal income tax is generally progressive, and substantially so. Click here to see the numbers. The average tax rate for tax returns with over $1 million in income is 25 percent. The average tax rate for returns with income between $50,000 and $75,000 is 7 percent.
2. It is arguably better to use an average tax rate that is all-inclusive. That is, we should include not only personal income taxes but also payroll and corporate income taxes. CBO analysts regularly do that. They find a substantially progressive tax system, as I have pointed out before.
3. If we added transfer payments (which are essentially negative taxes), we would find an even more progressive fiscal system. Those data are harder to come by, as data on transfers are rarely integrated with data on taxes.
4. It make little sense to aggregate payroll taxes with personal income taxes and ignore corporate income taxes.