Effective Middle Class Tax Rate in 2005: 14.2%

In 2005, the CBO data indicate that in the middle fifth, the total effective tax rate -- the share of federal taxes as a percent of income -- was 14.2 percent, while the effective individual income tax rate was 3.0 percent. These figures compare to 2000 levels of 16.6 percent and 5.0 percent, respectively. Between 2003 and 2005, the total effective tax rate for the middle fifth edged up, but still remained far below the levels of the previous 24 years.

source and source

(HT: Greg Mankiw)