Illinois Income Tax Calculator (flat 4.95%, 2026 exemption $2,925, per paycheck)

Understanding the Illinois income tax calculator — concept and principle

This calculator estimates Illinois state income tax for 2026 from your Illinois base income and number of exemptions. It shows the tax, the effective rate, the exemption allowance, net income taxed, tax per paycheck and income after Illinois tax. Use it for budgeting, checking withholding or comparing take-home pay across states.

After the exemption, every dollar is taxed at the same 4.95%, so the effective rate is a little lower.

How it is calculated

Exemption allowance = $2,925 × number of exemptions (2026).
Net income = Illinois base income − exemption allowance.
Tax = 4.95% × net income.
Effective rate = tax ÷ base income.
Tax per paycheck = yearly tax ÷ number of paychecks.

Base income starts from federal AGI with Illinois additions and subtractions. Credits such as the property tax credit are not included.

The principle

Illinois uses a flat income tax: every dollar of net income is taxed at the same 4.95% rate. The exemption allowance shields a fixed amount per person, so the effective rate is slightly below 4.95% and rises toward it as income grows. The allowance is adjusted for inflation; for 2026 it rose from $2,850 to $2,925. Your employer's withholding depends on the allowances you claim on Form IL-W-4, so actual paycheck amounts may differ.

Worked example

Default inputs: base income $75,000, 1 exemption, 26 paychecks.

Exemption allowance = $2,925.
Net income = 75,000 − 2,925 = $72,075.
Tax = 4.95% × 72,075 ≈ $3,568.
Effective rate = 3,568 ÷ 75,000 ≈ 4.76%.
Per paycheck = 3,567.71 ÷ 26 ≈ $137.22; income after Illinois tax ≈ $71,432.

Each point is the calculator re-run with only “Illinois base income (USD)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Illinois base income (USD)	Illinois income tax (USD)
18,750	783
37,500	1,711
56,250	2,640
75,000	3,568
93,750	4,496
112,500	5,424
150,000	7,280

How to read the result

Because the rate is flat, each extra $1,000 of income adds $49.50 of Illinois tax. Compare the tax per paycheck with your pay stub to check withholding. Federal income tax, Social Security and Medicare are separate and not included.

Common mistakes

Using gross wages instead of Illinois base income.
Forgetting extra exemptions for a spouse or dependents.
Using the 2025 allowance of $2,850 for 2026.
Expecting withholding to match exactly; it depends on your IL-W-4.

Keep in mind: Some exemptions and credits have income limits and special rules. Check the Illinois Department of Revenue instructions or a tax professional. This is not tax advice.

Frequently asked questions

What is the Illinois income tax rate?

A flat 4.95% of net income.

How much is the Illinois exemption for 2026?

$2,925 per exemption.

Does Illinois have tax brackets?

No. It uses one flat rate for all individual income.

Sources: Office of the Illinois Comptroller, Payroll Bulletin 1-26, "Illinois State Income Tax Exemptions – 2026" (5 Jan 2026)

Checked 9 Nov 2026. Office of the Illinois Comptroller, Payroll Bulletin 1-26 “Illinois State Income Tax Exemptions – 2026” (5 Jan 2026): rate remains 4.95%, exemption rises from 2,850 to 2,925 USD.

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