The amount of federal income tax that comes out of a person's paycheck depends on the person's number of exemptions, salary deductions (such as health insurance), marital status and earnings. The person's taxable gross wages is equal to the person's gross earnings (wages before deductions) plus taxable fringe benefits plus taxable employer-paid benefits minus any pre-tax deductions.
A person's taxable gross income and marital status will determine the marginal tax rate the person will have to pay. Although a person may have a marginal tax rate such as 28 percent and an income of $40,000, not all of the $40,000 in wages will be taxed at that rate. Due to the use of income brackets that each have their own tax rates, parts of it would be taxed at 10 percent, 15 percent or 25 percent. The federal tax brackets and rates can change on an annual basis.