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In recent years, however, a reduction in the tax rates applicable to capital gains, as well as dividend income, has significantly reduced the income tax burden on non-wage income. An argument is often made that these types of income are not generally received by low-income taxpayers, and so this sort of "tax break" is anti-progressive. Further clouding the issue of progressivity is that far more deductions and tax credits are available to higher-income taxpayers. A taxpayer with $40,000 of wage income may only have the "standard" deductions available to him, whereas a taxpayer with $200,000 of wage income might easily have $50,000 or more of "itemized" deductions. In those two scenarios, assuming no other income, the tax calculations would be as follows for a single taxpayer with no dependents in 2006:

Wage income $40,000 $200,000

Allowable deductions 8,450 51,430

Taxable income 31,550 148,570

Income tax 4,445 46,725

Effective rate 14% 31%

At first glance, this would appear to be highly progressive - the person with the higher taxable income pays tax at twice the rate. But this does not give the complete picture. If you divide the tax by the amount of gross income (i.e. before deductions), the effective rates are 11% and 23%: the higher income person's rate is still twice as high, but his deductions drive down the effective rate to a much greater degree. In addition, most discussions of income tax progressivity do not take into account the social security tax, which has a "ceiling". To expand the above example:

Social security tax $3,060 $8,740

Total tax 7,505 55,465

Rate paid on gross income 19% 28%

In other words, social security tax drives the effective rate up drastically for the low-income as opposed to the high-income taxpayer. This effect would be even more dramatic if the high-income taxpayer had $100,000 of wages and $100,000 of dividends and capital gains. In that case his total income tax would be $35,638, plus $7,290 of social security tax, for a rate on gross income of 21% - very near the rate paid by the low income wage-earner.

Progressivity, then is a complex topic which does not lend itself to simple analyses. Given the "flattening" of tax burden over the years, many commentators note that the general structure of the U.S. tax system has begun to resemble a partial consumption tax regime.[9]

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