How to Fill Out the IL-W-4: Illinois Employee Withholding Allowance Certificate

To fill out the IL-W-4, work through the two-step worksheet at the top of the page to count your allowances, carry those totals down to Lines 1 and 2 of the certificate, add any extra withholding you want on Line 3, then sign the certificate and hand it to your employer on or before your first day of work.¹ The form tells the employer how much Illinois income tax to hold back from each paycheck at the state’s flat 4.95 percent rate.²

Getting a Blank Form

New hires usually get an IL-W-4 from their employer’s payroll or HR office. If you need to update your withholding mid-job, download the current version from the Illinois Department of Revenue’s withholding forms page.³ The page has a worksheet on top and a certificate on the bottom. You keep the worksheet. Your employer keeps the certificate.

Step 1: Count Your Basic Allowances

Step 1 covers you, your spouse, and dependents.

Check the first box if no one else can claim you as a dependent.
Check the second box if you can claim your spouse as a dependent.
On Line 1, write the number of boxes you checked.
On Line 2, write the number of other dependents you plan to claim on your Illinois return.
Add Lines 1 and 2 and put the total on Line 3.
On Line 4, write the number of basic allowances you actually want to claim, anywhere from zero up to the Line 3 total.¹

The Line 4 figure is the one that carries down to the certificate.

Step 2: Count Your Additional Allowances

Step 2 picks up extra allowances for age, blindness, and certain deductions. Check a box for each of the following that applies: you are 65 or older, you are legally blind, your spouse is 65 or older, your spouse is legally blind. Enter the number of boxes checked on Line 5.¹

On Line 6, enter any amount you reported on Line 4 of the federal Form W-4’s Deductions Worksheet, plus any Illinois-specific subtractions or deductions you expect. Divide the Line 6 amount by 1,000 and round to the nearest whole number on Line 7. Add Lines 5 and 7 for the Line 8 total. On Line 9, write the number of additional allowances you actually choose to claim, up to the Line 8 total. Line 9 is what you carry down to the certificate.¹

Fill In the Certificate

The bottom portion of the page is the certificate. Above the numbered lines, enter your full legal name, Social Security number, and current mailing address. Verify the Social Security number against your card; a mismatch can jam things up when the Department of Revenue tries to reconcile your withholding to your annual return.

Then complete the three lines:

Line 1: your total basic personal allowances from worksheet Line 4.
Line 2: your total additional allowances from worksheet Line 9.
Line 3: any extra dollar amount you want withheld from each paycheck on top of what the allowances produce.¹

Line 3 is optional. It’s useful when you have income that isn’t subject to withholding, like freelance earnings, rental income, or investment gains, and you’d rather pay through payroll than write a check in April. Sign and date the certificate before you hand it over.

What Each Allowance Is Actually Worth

For tax year 2026, each Illinois personal exemption allowance is $2,925.⁴ Your employer multiplies your total allowances (Lines 1 and 2 combined) by that amount, subtracts the result from your annualized pay, and applies the 4.95 percent rate to what’s left.² More allowances mean less tax withheld each payday; fewer allowances mean more. The total you owe for the year is the same either way. The choice is really about timing.

If You Qualify as Exempt

You can skip Lines 1 through 3 entirely if you expect to owe no Illinois income tax for the year and you are also exempt from federal withholding. Check the exempt-status box on the certificate, then sign and date it.¹ Your employer will then withhold nothing for Illinois. Be careful: if it turns out you do owe tax, the full amount comes due when you file, along with possible penalties. This option is really only appropriate for very low earners or people whose credits and deductions genuinely erase their liability.

If You Live in Iowa, Kentucky, Missouri, or Wisconsin

Illinois has reciprocal income-tax agreements with those four states. If you live in one of them and work in Illinois, you are generally exempt from Illinois withholding and owe tax only to your home state. You do not file an IL-W-4 in that case. You file Form W-5-NR, the Employee’s Statement of Nonresidence in Illinois, with your employer instead.¹ Military spouses covered by the federal Military Spouses Residency Relief Act also use Form W-5-NR. Residents of any other state working in Illinois have Illinois tax withheld normally.

Turning It In and Updating It Later

Give the completed certificate to your employer’s payroll office on or before the day you start work. You do not send it to the Illinois Department of Revenue yourself. Your employer keeps it on file and uses it to run payroll. If you don’t submit a valid IL-W-4, or if you turn one in that is incomplete, unsigned, or altered, your employer is required to withhold Illinois tax on your entire compensation without any exemptions.¹ That produces much larger deductions than most people would actually owe.

Hand in a fresh IL-W-4 whenever your allowance count changes. Common triggers: marriage, divorce, a new child, a spouse who starts or stops working, turning 65, or going blind. A big balance due on your last IL-1040 is a signal to reduce allowances or add withholding on Line 3. A big refund is a signal you may be over-withholding.

Mistakes vs. Fraud

Honest errors, like miscounting dependents or forgetting to update after a divorce, don’t carry their own penalty. You’ll owe the difference when you file your IL-1040, plus interest on any underpayment. Illinois uses the federal underpayment rate, reviewed every January 1 and July 1.⁵

Filing a false certificate on purpose is different. Illinois imposes a fraud penalty of 50 percent of the tax deficiency attributable to the fraudulent act.⁵ Inventing dependents to zero out your withholding is the classic example, and the Department of Revenue can cross-check the allowances you claimed on the IL-W-4 against the ones you actually claim on your return.

1
Illinois Department of Revenue. Form IL-W-4 Employee’s and Other Payee’s Illinois Withholding Allowance Certificate and Instructions
2
Illinois Department of Revenue. Income Tax Rates
3
Illinois Department of Revenue. 2026 Withholding (Payroll) Tax Forms
4
Illinois Department of Revenue. FY 2026-15, What’s New for Illinois Income Taxes
5
Illinois Department of Revenue. Pub-103, Penalties and Interest for Illinois Taxes