Illinois charges 4.95% flat state income tax. Use the side income tax calculator pre-loaded with Illinois rates.
Open Side Income Tax Calculator →Side income in Illinois is subject to federal income tax at your marginal rate, self-employment tax if applicable, and a flat 4.95% Illinois state income tax. Because side income typically stacks on top of your W-2 salary, it is often taxed at your highest marginal rates. The combined marginal rate on side income can easily exceed 40% for mid-to-high earners. This calculator breaks down exactly what you keep from each dollar of side income in Illinois.
Illinois levies a flat 4.95% state income tax on all taxable income regardless of how much you earn. This makes tax planning straightforward: for every additional dollar you earn, 4.95 cents goes to Illinois. Illinois does not impose local income taxes, so the 4.95% flat rate is the only state-level income tax you owe.
The table below shows what you actually keep at five salary levels in Illinois, accounting for federal tax, FICA, and Illinois's flat 4.95% state tax.
See how Illinois compares to other Midwest states. Each link takes you to the side income tax calculator landing page for that state.
For a comprehensive breakdown of Illinois’s tax structure, salary comparisons, cost-of-living analysis, and more, visit the full Illinois take-home pay page.