Overview
Illinois keeps things simple with a flat state income tax rate. There are no filing statuses to track—the calculation is based entirely on the employee’s basic and additional allowances from Form IL-W-4.
State Income Tax (SIT)
Illinois imposes a flat state income tax rate of 4.95% for 2026. Withholding is straightforward: employees claim basic allowances (worth $2,925 each) and additional allowances (worth $1,000 each) on Form IL-W-4. There is no standard deduction and no filing status selection. The supplemental rate matches the regular rate at 4.95%.
| Tax Structure | Flat rate: 4.95% |
| State Withholding Form | Form IL-W-4 |
| No Filing Statuses | Calculation based on allowances only |
| Basic Allowance Value | $2,925 per allowance |
| Additional Allowance Value | $1,000 per allowance |
| Supplemental Rate | 4.95% |
Supplemental Wages
Illinois supports the following supplemental calculation methods. When using the flat method, the supplemental rate is 4.95%.
Employer State Unemployment Tax (SUTA)
Your assigned SUTA rate will be based on your company’s experience with unemployment claims. New employers typically start at the default rate of 3.175%.
| Tax Type | Employer-paid only |
| Default New Employer Rate | 3.175% |
| Rate Assignment | Experience-rated; assigned annually by the state |
Other Taxes & Obligations
Illinois does not currently impose significant additional state-level payroll taxes beyond SIT and SUTA. This keeps payroll relatively streamlined compared to states with multiple layers of tax obligations.
Disclaimer: This content is provided for general informational purposes only and does not constitute legal, tax, or accounting advice. Netchex does not provide tax or legal guidance and makes no representations regarding the accuracy or applicability of this information. Laws and regulations may change. The information on this page reflects payroll tax guidelines as of March 2026. For the most current requirements, please refer to: Illinois Department of Revenue
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