Calculating the Iowa income school district surtax is not complicated. Under Iowa law, any resident earning a net income over $9,000 or a married couple filing a joint return earning a net income over $13,500 must file an Iowa income tax return. The county and school district where the taxpayer resides determine the income school district surtax rate to be charged to the taxpayer's income. The Iowa income school surtax is a local option tax adopted upon voter approval for the purpose of funding educational improvement programs in a school district.
Calculate your Iowa taxable income on Form 1040. Subtract the amount determined from Line 41, your standard and itemized total deductions, from the amount determined on Line 36, the portion of your income subject to taxation.
Calculate your Iowa income tax owed. Add your Iowa income tax liability to any Iowa lump-sum tax owed and any Iowa minimum tax owed to determine the total amount of taxes you owe. Subtract from Line 46, the total tax you owe, all credits you can claim. If you qualify to receive a nonresident or part-year resident credit, or some other nonrefundable Iowa credit, subtract these credit amounts as well from your total taxes owed.
Locate the Iowa income school district surtax rate that applies to the county and school district where you reside. Your applicable school district and county for tax purposes is the one in which you resided on the last day of the tax year. You can view this information online at the Iowa Department of Revenue website. For instance, in 2010 a resident of Butler County living in the Nashua-Plainfield School District would have been charged a school income surtax rate of 11 percent.
Multiply the Iowa income school district surtax rate by the your Iowa total income tax liability minus any credits you claimed. For instance, if you had a total Iowa income tax liability of $3,333 and you lived in the Nashua-Plainfield School District, which has an 11 percent income surtax, you would owe $366.63. To do this calculation, multiply the Iowa state income tax amount due, $3,333, by 0.11 to arrive at your Iowa income school surtax of $366.63.
Add your Iowa total income tax liability, Line 54, to your income school district surtax taxes owed, Line 55. Record this information on Line 56 of your 1040 form.