Illinois Flat Income Tax Explained
Illinois is one of a handful of states that uses a flat income tax rate rather than a progressive bracket system. Every wage earner in Illinois pays the same 4.95% rate on their taxable income, regardless of whether they earn $30,000 or $3 million. This flat structure simplifies tax calculations and means your state tax withholding is a predictable percentage of each paycheck.
In 2020, Illinois voters rejected a proposed constitutional amendment that would have replaced the flat tax with a graduated rate structure. The failed measure would have imposed higher rates on higher earners while reducing rates for lower incomes. With that proposal defeated, the flat 4.95% rate remains locked in, protected by the Illinois Constitution which mandates that any income tax must be applied at a single, uniform rate.
Personal Exemptions and Deductions
Illinois provides a personal exemption of $2,625 that reduces your taxable income before applying the flat rate. Married couples filing jointly receive a combined exemption of $5,250, with additional exemptions available for qualifying dependents. Unlike the federal system, Illinois does not offer a standard deduction in the traditional sense— instead, it starts with your federal adjusted gross income and applies the personal exemption.
Illinois also does not allow itemized deductions at the state level. Your state tax is calculated on your federal AGI minus the personal exemption amount. Some specific subtractions are available, including federally taxed Social Security income, retirement income, and military pay. Certain property tax credits and education expense credits can further reduce your state tax liability.
Local Taxes and Special Considerations
Most Illinois residents pay no local or city income tax, which keeps the state payroll calculation simple. However, a small number of municipalities (primarily in the southern part of the state) levy modest local income taxes. The vast majority of workers in Chicago and the surrounding suburbs are only subject to the state flat tax and federal obligations.
One of Illinois' most notable tax features is its complete exemption of retirement income from state tax. Social Security, pensions, 401(k) distributions, and IRA withdrawals are all exempt. While this does not affect your working-age paycheck calculation, it makes Illinois an attractive state for retirement planning. Workers contributing to retirement accounts can rest assured those withdrawals will not be taxed by the state when they eventually draw on them.