Taxpayers use income tax tables in order to determine their tax liability, says TurboTax. Although tax tables do not directly indicate your tax rate, you can determine your average tax rate using the amount of taxes that you owe according to a tax table, according to eFile.com. To do so, divide your tax liability by your total income, then multiply the quotient by 100.
In order to find your tax liability using the federal tax tables found in IRS Publication 17, first determine your filing status, says Turbotax. This includes head of household, married filing jointly, married but filing separately, and individual. Then, using your taxable income, find the row with the income bracket that includes your income amount in the left hand column of the tax table. Next, select the column containing your filing status, and use the number at the intersection as the amount that you owe.
As of 2015, you may only use a tax table if your income is less than $100,000, warns the IRS. If your income exceeds $100,000, you must use a tax computation worksheet. These worksheets allow you to apply a multiplication amount to your total income and then subtract an amount to determine your tax liability. Additionally, you may find your marginal tax rate and the tax rates applicable to each portion of your income in the tax rate schedules section of Publication 17. Although you may not use these schedules to directly calculate your taxes, you may use them to identify your marginal tax rate, which is the rate you pay on each additional dollar of income.