In the USA, after all allowable deductions are subtracted from income, income tax is figured at a rate of 10%, 15%, 25%, 28%, 33% or 35%. In the USA those are called brackets rather than slabs as in India. The first $x of taxable income is taxed at 10%, then the next $y at 15%, etc until the total tax has been calculated, The amount of dollars taxed in each bracket depends on the person's filing status. A person may file as single, married filing jointly, married filing separately, or head of household - there are different tables for each filing status. You can see the tables at irs.gov - go to more forms and publications, then to form and instruction number, then scroll down to 2007 Inst 1040 Instructions and look for Tax Rate Schedules.