Illinois state income tax
Primary form: IL-1040
State tax in BasilTax: Yes — we calculate it for you
Structure: flat
Flat 4.95% on base income after exemptions.
Verify your return
Upload your W-2s and 1099s, assign them to a return, and run compute. For states we support end-to-end, BasilTax applies that state’s own rules—brackets, deductions, and the usual quirks—so your state tax lines up with your federal return.