Illinois is the simplest schedule in this batch to describe and the easiest to misread. There is one rate, 4.95 percent, and no standard deduction in the Tax Foundation table, so the calculator figure is simply 4.95 percent of the full $80,000 salary. The catch is the personal exemption, which sits beside that figure rather than inside it, so a return may come out lower than the calculator shows.
Enter your salary and filing status to see the Illinois line alongside federal tax and FICA.
The worked example, with nothing to subtract first
Take a single filer with an $80,000 salary and no pre-tax deductions. With no standard deduction in the table, taxable income for the calculator is the full $80,000, and the state tax is $80,000 multiplied by 4.95 percent, which is $3,960. Paid biweekly, that is about $152.31 per paycheck. The marginal rate and the effective rate on gross pay are the same number, 4.95 percent, because there is no deduction to drive them apart.
That sameness is itself the point to understand. In most states, the effective rate on gross pay sits below the marginal rate because a deduction shields part of the salary. In Illinois, on the calculator's basis, nothing is shielded, so every dollar of salary is taxed at the same rate, and a raise is priced at exactly 4.95 cents per extra dollar.
The exemption the calculator does not subtract
Illinois gives a personal exemption of $2,925 single and $5,850 joint, and that exemption is not in the standard deduction fields. That $3,960 is the calculator's number, so it agrees with the tool, while a return that claims the exemption would show a lower taxable income. Do not add the exemption to the calculator figure and do not subtract it twice; treat the $3,960 as the calculator's figure and the exemption as the reason a filed return can differ from it.
Source for the rate: Tax Foundation 2026 State Income Tax Rates and Brackets. Treat this as general information about Illinois's schedule, not a determination for an individual return. The federal brackets guide, linked from the paycheck hub, covers the federal slice on the same salary.
FAQs
Does Illinois really have no standard deduction?
There is no standard deduction in the Tax Foundation table for Illinois. The state uses a personal exemption instead, which is a different mechanism and is not subtracted in the calculator figure.
Why might my Illinois return be lower than $3,960?
Because the personal exemption of $2,925 single or $5,850 joint is not subtracted in the calculator figure. Claiming it lowers taxable income, so the filed tax can come out below the calculator's figure.
Does filing jointly change Illinois's rate?
No, the rate stays 4.95 percent, and with no standard deduction in the table, the calculator figure at $80,000 is $3,960 for both single and joint filers. The difference is the larger joint exemption, which sits outside the calculator figure.