The majority of Americans have to do two completely separate tax returns, one for the federal taxes and one for the state in which they live. For Georgia residents, calculating taxable income for Georgia state income tax involves slightly different calculations than a federal 1040, but the general framework that the state uses is similar to what you'll find in dealing with the IRS.

How Georgia taxes work
The state of Georgia generally follows the provisions of federal law in determining adjusted gross income. In November 2015, the state's governor signed a law that adopted all federal provisions on or before Jan. 1, 2015 for use on state individual income tax forms.

As a result, the starting point for Georgia taxable income is your federal adjusted gross income. This includes wages, investment income, business income, and income from other taxable sources, with reductions for items such as deductible IRA contributions, half of your self-employment taxes, and other amounts that you can use to reduce adjusted gross income. The most common adjustment that you have to make is if you earned interest on tax-exempt bonds outside Georgia, which are exempt from federal tax but not from Georgia state tax and therefore must be added back to your Georgia adjusted gross income.

Georgia also allows taxpayers to exclude up to a maximum amount of retirement income from their Georgia adjusted gross income. For 2015, those who are 65 or older can exclude up to $65,000 of certain types of income, while those between 62 and 64 or who are permanently disabled can exclude up to $35,000.

Once you know your adjusted gross income, you then have to make allowances for personal exemptions and other deductions. These amounts differ from their federal counterparts. In 2015, married couples are allowed personal exemptions of $3,700 each, while single filers can claim a $2,700 exemption amount. An additional $3,000 is allowed for each dependent in the household.

Georgia's standard deductions are also smaller than what federal law provides, with single filers getting a $2,300 standard deduction while joint filers getting $3,000. Those who are 65 or older or are blind get an extra $1,300 added to their standard deduction. If you used the standard deduction for your federal return, you must use it for your Georgia return as well, even if you'd get a bigger deduction by itemizing. Those who itemized, however, can use the higher federal itemized amount.

Your Georgia taxable income will be your adjusted gross income less your personal exemptions and standard or itemized deductions. Tax rates of between 1% and 6% will then apply depending on your tax bracket to determine your total tax due.

Calculating your Georgia taxable income isn't too complicated, but you do have to take account of differences from federal tax law. Otherwise, you'll end up paying the wrong amount of tax and cause unnecessary problems.

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