How Iowa income tax works: federal taxable income, a flat 3.8%, and the school surtax

Iowa’s income tax is built on one decision made in 2022: the IA 1040 starts from federal taxable income, line 15 of Form 1040, not from adjusted gross income. That is the number after the standard or itemized deduction, after the qualified business income deduction, and after every new federal deduction of 2025, for tips, overtime, car-loan interest and seniors. All of it is already out before Iowa sees a dollar. Iowa then subtracts a few things of its own, mainly retirement income for anyone 55 or older and all Social Security, adds back even fewer, and multiplies the result by 3.8%. There are no brackets and no Iowa standard deduction. In place of a personal exemption there are small credits against the tax, $40 a person. Then most school districts add a surtax of their own, a percentage of the Iowa tax rather than of income. The return is due April 30, not April 15.

The starting point explains most of what surprises people. A tipped worker who owes no federal tax on $8,000 of tips owes no Iowa tax on them either. A couple’s $32,200 federal standard deduction comes off the Iowa return too, worth $1,224 at 3.8%. And when Congress changes a deduction, Iowa changes with it: Iowa Code 422.3(5)(b) defines the Internal Revenue Code as the code “as amended,” and the Department of Revenue said in its November 2025 withholding notice that the Iowa Code “is automatically conformed” to the federal one. The 2026 session enacted nothing to decouple.

Who files

A full-year resident reports all income, wherever it was earned, and takes a credit on IA 130 for tax paid to another state on income taxed by both. A part-year resident or nonresident files the same IA 1040, figures the tax on everything, and then takes a credit on IA 126 for the share that was not Iowa’s. Nonresidents must file when Iowa-source net income is $1,000 or more. Residents must file when income is more than $9,000 single or $13,500 on a joint, head of household or surviving spouse return, or $24,000 and $32,000 when 65 or older; for this test the standard or itemized deduction, the QBI deduction and the senior deduction are added back to Iowa taxable income. Those are the 2025 figures; they are not indexed and the 2026 instructions were not out at this writing. Anyone with Iowa withholding files to get it back, and anyone eligible for the refundable Iowa earned income credit should file whether or not a return is required.

Where it starts: federal taxable income

The first six lines of the IA 1040 are copied from the federal return for information only: total income, adjustments, AGI, the standard or itemized deduction, the QBI deduction, and, new for 2025, the senior deduction on line 1f. Line 2 is federal taxable income from Form 1040 line 15, and the form says so plainly: “Do not include lines 1a through 1f.” If federal taxable income is zero, Iowa lets you work out the negative figure and carry it, which matters when Iowa subtractions are large.

Because the starting point is below the line, every federal deduction counts in Iowa: the standard deduction, $16,100 single and $32,200 joint for 2026 with the additions at 65; itemized deductions exactly as claimed on Schedule A, state income tax included within the $40,000 SALT cap, with no Iowa add-back; the 20% qualified business income deduction; the July 2025 deductions for tips, overtime, car-loan interest and the $6,000 senior deduction, all taken on federal Schedule 1-A on the way to line 15; and the charitable deduction for non-itemizers. The Iowa return never asks about any of them. It inherits the answer.

The Iowa modifications: Schedule 1

Line 3 of the IA 1040 is the net of Iowa’s additions and subtractions from IA 1040 Schedule 1. For most households only two or three of its lines are ever used.

Line 2 plus line 3 is Iowa taxable income on line 4. Iowa’s deduction for federal income tax paid ended after 2023 and is not on the schedule.

The retirement lines are the big ones and have their own article, Iowa for retirees. The 529 deduction is the one most often missed, because the federal return never asks about it; see Credits and breaks for Iowa families. The capital gain deduction was once broad and is now narrow: farm real property held ten years with material participation or sold to a relative, retired farmers’ livestock, employee-owners’ stock in a qualified Iowa corporation, and installments on pre-2023 sales. A house, a business or a brokerage account gets nothing.

No standard deduction, and $40 credits instead of exemptions

Iowa has no standard deduction, itemized deductions or personal exemption deduction of its own, because the federal ones already did the work. What it has are exemption credits against the tax on line 8: $40 for the taxpayer, $40 for a spouse on a joint return (and a second $40 on a head of household return as well), $40 for each dependent claimed federally, and $20 more for each taxpayer who is 65 by January 1 following the tax year or who is blind. A married couple with two children claims $160; a retired couple both over 65 claims $120. A dependent who files their own return still takes the $40.

Below the filing thresholds there is a low-income exemption: if income, with the deductions added back as above, is $9,000 or less single or $13,500 or less joint, head of household or surviving spouse, or $24,000 and $32,000 at 65 or older, Iowa tax is zero. A tax-reduction worksheet and an alternate tax computation smooth the cliff just above the line; the software runs both.

The rate

Iowa taxable income on line 4 times 3.8% is the Iowa tax on line 5. That is the entire computation. Wages, interest, dividends, long-term capital gains, rent, gambling winnings, unemployment: all at 3.8%. There is no preferential rate for gains, so a $20,000 long-term gain in the federal 0% bracket still costs $760 here, and no alternative minimum tax since 2023. Iowa Code 422.5(1)(a) sets the rate “at a rate of three and eight-tenths percent,” and the Department’s October 21, 2025 announcement confirmed that “all levels of taxable individual income will be subject to this rate” for 2026.

The credits

The nonrefundable credits on lines 8 through 17 reduce the tax but cannot produce a refund; the refundable ones on lines 23 through 27 are paid out even when no tax is left. Two are percentages of a federal credit, so the 2025 federal changes to those credits reach Iowa as well.

Iowa has no child tax credit; the federal one reduces federal tax, not taxable income, so it never touches the Iowa return. The family credits are in Credits and breaks for Iowa families. There is no renter or homeowner credit on the return either; property tax relief runs through the county.

The school district surtax

Iowa has no city or county income tax, but most school districts levy an income surtax, figured as a percentage of tax rather than of income. Line 19 multiplies the Iowa tax after nonrefundable credits, line 18, by the rate of the school district where you lived on December 31. The 2025 rates run from 0% to 20%: roughly fifty districts, Burlington and Waterloo among them, levy nothing, and Postville, Fremont-Mills and East Mills are at 20%. Residents of Appanoose, Cass, Pocahontas, Sac, Shelby and Winnebago counties pay a further 1% for emergency medical services. The district number goes on page 1, and the 2026 list is to come with the 2026 forms. A family whose Iowa tax is wiped out by credits owes no surtax, a retiree whose income is all subtracted owes none, and a mover pays the rate of the district they lived in on the last day of the year.

Withholding and estimated payments

Iowa withholding on wages is figured from the IA W-4 at the flat rate, with the standard deduction and exemption credits built into the formula; the Department revised both for 2026 to reflect the federal law. One gap remains: the IA W-4 has no line for the tips, overtime or car-loan interest deductions, so a worker with any of them is over-withheld all year and collects the Iowa saving at filing. Seniors can file a new IA W-4 for the senior deduction. Retirees 55 and older certify on the IA W-4P that no Iowa withholding is needed on a pension or IRA.

Estimated payments are required when the Iowa tax expected after withholding and credits is $1,000 or more, up from $200 for 2026. They go on IA 1040ES or through EasyPay Iowa on Iowa’s own dates: April 30, June 30, September 30 and January 31. The IA 2210 penalty is figured as the federal one is, and the safe harbors follow the federal pattern of 90% of this year’s tax or 100% of last year’s, with no 110% tier. Farmers and fishers may pay once by January 15, 2027, or file and pay in full by March 1, 2027, with IA 2210F. Interest on late payments is 10% a year for 2026.

How to file

The IA 1040 is due April 30, 2027. Most returns go in electronically with the federal return; Iowa has no free software of its own but takes part in the Free File Alliance, and VITA and AARP Tax-Aide sites prepare both returns at no charge. Payments go through EasyPay Iowa; account letters and refund status are on GovConnectIowa and the Department’s Where’s My Refund page.

The extension is unlike the federal one. There is no form and no request. Anyone who has paid at least 90% of the final Iowa tax by April 30, through withholding, estimates or a payment with voucher IA 1040V, automatically has until November 1, 2027 to file, with interest on the balance. A federal Form 4868 does nothing for Iowa. Pay less than 90% by April 30 and there is no extension at all; the late-filing and late-payment penalties both apply. The dates and forms are gathered in Iowa calendar and forms.

What trips people up

• Retirement income left in Iowa income because software carried the 1099-R to the federal lines and nobody checked Schedule 1 line 7.
• An ISave 529 contribution nobody mentioned, because the federal return did not ask.
• The wrong school district number, or the old one after a move. The surtax follows the district on December 31.
• Estimated payments skipped on the old $200 threshold, or made on the federal dates. Iowa’s are April 30, June 30, September 30 and January 31.
• A federal extension treated as an Iowa extension. Iowa’s is automatic, but only when 90% is paid by April 30.