Here's the Federal Income Tax info. Most states also have income taxes, in addition to this.
Wikipedia is awesome
Example of a tax computation
Income tax:
* $40,000 (adjusted gross income)
o $7,550 × 0.10 = $755
o ($30,650 - $7,550) × 0.15 = $3,465
o ($40,000 - $30,650) × 0.25 = $2,337.50
* Total income tax = $6,557.50 (16.39% of income)
Note that in addition to income tax, a wage earner would also have to pay FICA (payroll) tax (and an equal amount of FICA tax must be paid by the employer):
* $40,000 (adjusted gross income)
o $40,000 × 0.062 = $2,480 (Social Security portion)
o $40,000 × 0.0145 = $580 (Medicare portion)
* Total FICA tax = $3,060 (7.65% of income)
* Total federal tax of individual = $9,617.50 (24.04% of income)