Estimate your Illinois state income tax plus combined federal and IL state tax for 2026. 4.95% flat rate.
Illinois has a constitutionally mandated flat income tax rate of 4.95% on all taxable income. Illinois cannot implement a graduated income tax without a constitutional amendment. Illinois residents often face high property taxes alongside the flat income tax. Use the calculator above to estimate your combined federal and Illinois state income tax for 2026. State tax figures use a simplified rate — for precise Illinois state tax calculations, consult the Illinois Department of Revenue or a licensed tax professional.
Illinois has a 4.95% flat rate state income tax for 2026. Illinois has a constitutionally mandated flat income tax rate of 4.95% on all taxable income. Illinois cannot implement a graduated income tax without a constitutional amendment. Illinois residents often face high property taxes alongside the flat income tax. The state income tax is calculated separately from federal income tax and is paid through payroll withholding or quarterly estimated payments.
Illinois has its own state standard deduction separate from the federal standard deduction ($15,750 single, $31,500 MFJ in 2026). For precise Illinois state deduction amounts, consult the Illinois Department of Revenue or a state tax professional.
Illinois's 4.95% flat rate state income tax can be compared to other states using our state tax calculator above. The U.S. average top marginal state income tax rate is approximately 5-6%. Nine states have no income tax at all (Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington, Wyoming), while California has the highest at 13.3%.
Illinois offers state tax credits and deductions that may reduce your state tax liability. Common state credits include earned income credits, child tax credits, and credits for the elderly. Consult the Illinois Department of Revenue website or a licensed tax professional for credits specific to your situation and income level.
Use the calculator above. Enter your income and IL is pre-selected as your state. The calculator computes your 2026 federal income tax using the One Big Beautiful Bill Act brackets (10%-37%), adds your estimated Illinois state income tax (4.95% flat rate simplified), and displays your total tax burden, combined effective rate, and annual take-home pay. All calculations happen instantly in your browser.