How Paycheck Taxes Work in Illinois
How paycheck taxes work in Illinois: Your employer withholds federal income tax based on your W-4, then Illinois state income tax using state withholding tables. Social Security (6.2%) and Medicare (1.45%) are also deducted from each paycheck. Illinois uses a flat tax model, meaning every taxpayer pays 4.95% of their taxable income. This simplicity is balanced by a state standard deduction that reduces the overall taxable base. While the flat rate is moderate, residents in the Chicago metropolitan area should be aware of various local tax implications, although state income tax remains consistent throughout the state.
Illinois State Tax Information
Illinois utilizes a flat state income tax rate of 4.95% for the 2026 tax year.
Illinois uses a flat tax model, meaning every taxpayer pays 4.95% of their taxable income. This simplicity is balanced by a state standard deduction that reduces the overall taxable base. While the flat rate is moderate, residents in the Chicago metropolitan area should be aware of various local tax implications, although state income tax remains consistent throughout the state.
Illinois is a better state to model carefully when you are comparing job offers, relocations, or remote-work options because state withholding can materially change annual take-home pay.
Federal Income Tax
Federal income tax uses progressive brackets: higher income is taxed at higher rates, not all at one rate. The standard deduction reduces taxable income before brackets apply, and your W-4 affects how much is withheld through the year.
Social Security
Social Security tax (FICA) is 6.2% of wages up to the annual wage base ($184,500 in 2026). Both employee and employer pay this amount; this calculator shows the employee portion.
Medicare
Medicare tax is 1.45% on all wages with no cap. High earners pay an additional 0.9% on wages above $200,000 (single) or $250,000 (married filing jointly).