Illinois Income Tax Withholding 2026: Employer Guide

If you run a business in Illinois, here is the good news: the state uses a flat income tax rate. Unlike progressive-rate states such as California (which has rates ranging from 1% to 13.3%) or the federal income tax system with its multiple brackets, Illinois applies a single rate to all taxable income. That makes withholding calculations considerably simpler for employers.

However, "simpler" does not mean you can ignore the details. You still need to collect the right forms from employees, calculate withholding correctly, file returns on time, and make deposits on schedule. This guide walks through every step Illinois employers need to know about state income tax withholding in 2026.

The Flat 4.95% Rate

The Illinois Constitution requires the state to use a flat income tax rate — the same percentage applies to all taxable income, regardless of how much an employee earns. The current rate is 4.95%, which has been in effect since July 1, 2017.

What this means in practice:

• An employee earning $30,000/year and an employee earning $300,000/year are both taxed at 4.95% on their Illinois taxable income.
• There are no tax brackets to look up. No phase-outs or graduated schedules.
• You apply one rate to the taxable amount after allowances — that is the withholding.

Compare this to the federal system, where employers must handle seven tax brackets (10%, 12%, 22%, 24%, 32%, 35%, and 37%), or California, which has rates from 1% up to 13.3%. Illinois's flat structure removes that complexity entirely.

IL-W-4 Form

Every employee working in Illinois must complete Form IL-W-4 (Employee's and other Payee's Illinois Withholding Allowance Certificate). This is the state equivalent of the federal W-4 and tells you how much to reduce their withholding.

What the IL-W-4 Covers

• Line 1 — Basic Allowances: The employee claims allowances based on their filing status and personal exemptions. One allowance for themselves, one for a spouse (if applicable), and one for each dependent.
• Line 2 — Additional Allowances: Employees may claim additional allowances if they or their spouse are 65 or older or legally blind, or if they report deductions on the federal Form W-4 Deductions Worksheet or have other Illinois subtractions.
• Additional Withholding: Employees can request an additional flat dollar amount be withheld from each paycheck.
• Exempt Status: Employees who expect to owe no Illinois income tax may claim exemption from withholding.

How Allowances Reduce Withholding

Each allowance claimed on the IL-W-4 reduces the amount of wages subject to the 4.95% tax. The Illinois Department of Revenue publishes the per-allowance reduction amount each year. More allowances mean less withholding; fewer allowances mean more withholding.

When to Request a New IL-W-4

• At the time of hire (before the first paycheck)
• When an employee requests a change to their withholding
• The IL-W-4 does not expire, but employees should update it after major life events (marriage, divorce, new dependents)

How to Calculate Illinois Withholding

Calculating Illinois state income tax withholding is straightforward thanks to the flat rate. Here is the step-by-step process:

Step 1: Start with Gross Wages

Begin with the employee's gross wages for the pay period. This includes regular wages, overtime, bonuses, and commissions.

Step 2: Subtract the Allowance Amount

Using the number of allowances claimed on the employee's IL-W-4, subtract the corresponding allowance amount for the pay period. The Illinois Department of Revenue provides tables showing the per-pay-period value of each allowance (annual amount divided by number of pay periods).

For 2026 withholding, each Line 1 allowance is worth $2,925 a year and each Line 2 allowance is worth $1,000 a year. Divide the annual allowance value by the number of pay periods to get the per-period reduction:

• Weekly: Annual allowance value ÷ 52
• Biweekly: Annual allowance value ÷ 26
• Semi-monthly: Annual allowance value ÷ 24
• Monthly: Annual allowance value ÷ 12

Step 3: Multiply Taxable Amount by 4.95%

Take the result from Step 2 (gross wages minus allowance amount) and multiply by 0.0495. The result is the Illinois income tax to withhold for that pay period.

Example Calculation

Filing IL-941 Returns

Illinois employers report their state income tax withholding on Form IL-941 (Illinois Withholding Income Tax Return). Form IL-941 is filed quarterly, by the last day of the month after the quarter ends.

Quarterly Filing

Illinois employers file IL-941 on a quarterly basis through the MyTax Illinois online portal. Quarterly deadlines are:

Your payment schedule (below) can be monthly or semi-weekly, but the IL-941 return itself is always quarterly. Household employers can report household employee withholding on Form IL-1040 instead.

Payment Schedules

The Illinois Department of Revenue assigns your payment schedule based on the withholding you reported during the “look-back” period, the one-year period ending June 30 of the prior calendar year. For 2026, the look-back period is July 1, 2024, through June 30, 2025. The two schedules are:

Monthly Payers

First-time employers and employers that reported $12,000 or less in withholding during the look-back period pay by the 15th of the following month. For example, January withholding is due by February 15.

Semi-Weekly Payers

Employers that reported more than $12,000 in withholding during the look-back period, or that exceed $12,000 in withholding during a quarter, pay on a semi-weekly schedule:

• For amounts withheld on Wednesday, Thursday, or Friday: pay by the following Wednesday
• For amounts withheld on Saturday through Tuesday: pay by the following Friday

All payments should be made through MyTax Illinois for electronic payment. The system accepts ACH debit payments directly from your bank account.

Chicago Head Tax (Repealed)

Chicago's employer expense tax, known as the “head tax,” was a per-employee tax paid by employers, not an income tax. The City fully phased it out in 2014. A proposal to bring it back was removed from the City's FY 2026 budget before the City Council adopted it, so Chicago employers have no head tax to pay in 2026.

No Local Income Taxes

Unlike some states, Illinois does not allow municipalities to levy local income taxes. This is a significant advantage for employers operating in the state.

For comparison:

• Ohio: Over 600 municipalities levy local income taxes, each with different rates and rules. Employers may need to withhold for multiple cities.
• Pennsylvania: Hundreds of local earned income taxes (EIT) at varying rates, requiring withholding based on where employees live and work.
• Illinois: No municipal income tax.

This means Illinois employers only need to calculate and remit one state income tax withholding (the flat 4.95%) regardless of which city or county their employees live or work in. No local tax registrations and no split withholding between local jurisdictions.

Year-End Requirements

At the end of each calendar year, Illinois employers have several income tax withholding obligations to complete:

1. Provide W-2s to Employees

Furnish Form W-2 to every employee by January 31 of the following year. The W-2 must show Illinois wages and Illinois income tax withheld in the state-specific boxes (Boxes 15-17).

2. File W-2s with the Social Security Administration

Submit all W-2 forms to the Social Security Administration by January 31. Electronic filing (via the SSA's Business Services Online) is required for employers filing 10 or more W-2s.

3. File Your Fourth-Quarter IL-941

File your fourth-quarter IL-941 by January 31. Illinois does not require a separate annual reconciliation return. The total withholding reported across all four quarterly returns must match the total Illinois withholding reported on all employee W-2s. Any discrepancy will trigger a notice from the Department of Revenue.

4. File W-2s with Illinois

Illinois requires employers to submit copies of W-2s to the Illinois Department of Revenue. This can be done electronically through MyTax Illinois.

Common Withholding Mistakes

Even with Illinois's simpler flat-rate system, employers still make these common errors:

1. Not collecting the IL-W-4: Using only the federal W-4 and skipping the state form. The IL-W-4 is a separate, required document. The federal W-4 does not determine Illinois withholding.
2. Using the wrong rate: The rate is 4.95%, not 4.95 cents. Double-check your payroll system is calculating a percentage, not a flat amount.
3. Ignoring allowances: Withholding on the full gross wage without reducing for IL-W-4 allowances results in over-withholding. Employees will notice and complain.
4. Missing deposit deadlines: Knowing your payment schedule (monthly or semi-weekly) and depositing accordingly. Late deposits trigger penalties immediately.
5. Failing to reconcile at year-end: The total IL withholding on your quarterly IL-941s must match the total on all W-2s. Discrepancies trigger notices and potential audits.
6. Not updating for rate changes: While the rate has been 4.95% since 2017, always verify the current rate at the start of each year in case legislation changes it.
7. Withholding for non-resident employees incorrectly: Employees who work in Illinois but live in Iowa, Kentucky, Michigan, or Wisconsin may be covered by reciprocal agreements. Check the Illinois reciprocal withholding rules before withholding Illinois tax from these employees.

Frequently Asked Questions