How to Fill Out the Illinois Withholding Allowance Worksheet

The Illinois withholding allowance worksheet is the two-step calculator printed on the back of Form IL-W-4. You fill it out to figure how many allowances to claim, then copy two numbers onto the certificate at the top of the form and hand that certificate to your employer. Step 1 counts basic personal allowances for you, your spouse, and your dependents. Step 2 adds allowances for age, blindness, and deductions you expect to take. Keep the worksheet for your records; your employer only needs the certificate.¹

What Each Allowance Is Worth

Illinois taxes income at a flat 4.95 percent, and each allowance shelters $2,925 of annual income from withholding, with an extra $1,000 exemption for age or blindness.² In dollar terms, one allowance is worth roughly $145 less in state tax withheld across the year.³ Claim too many and you’ll owe at filing time; claim too few and you’ve lent the state money interest-free.

Step 1: Basic Personal Allowances

Step 1 has four lines.¹

Line 1. Check one box if no one else can claim you as a dependent, and a second box if you can claim your spouse as a dependent. Write 0, 1, or 2 to match the number of boxes you checked.
Line 2. Write the number of dependents, other than you or your spouse, that you will claim on your Illinois return.
Line 3. Add Lines 1 and 2. This is the maximum number of basic allowances you’re entitled to.
Line 4. Write the number you actually want to claim. Any figure from zero up to the Line 3 total is allowed. Choosing less than the maximum means more tax comes out of each check.

If you and your spouse both work and each file an IL-W-4, the form recommends putting all the allowances on the highest-paying job and claiming zero on the others. Splitting them across jobs tends to under-withhold.¹

Step 2: Additional Allowances

Skip Step 2 unless one of these applies: you or your spouse are 65 or older, you or your spouse are legally blind, or you entered an amount on Line 4 of the federal Form W-4 Deductions Worksheet. Otherwise, Step 2 has five lines.¹

Line 5. 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 total number of boxes checked. Each one represents a $1,000 exemption.²
Line 6. Enter the amount from Line 4 of the federal Form W-4 Deductions Worksheet, plus any Illinois-specific subtractions you expect (certain retirement income, for example).
Line 7. Divide Line 6 by 1,000 and round to the nearest whole number.
Line 8. Add Lines 5 and 7. This is the maximum number of additional allowances you can claim.
Line 9. Enter the number of additional allowances you actually want to claim, up to the Line 8 amount.

Line 6 is the place to fold in deductions that will lower your Illinois taxable income beyond the personal exemptions. Converting those expected deductions into allowances now keeps the state from over-withholding all year.

Moving Your Numbers to the Certificate

Once the worksheet is done, transfer the results to the three-line certificate at the top of the form.¹

Certificate Line 1. The number from Step 1, Line 4.
Certificate Line 2. The number from Step 2, Line 9. Leave blank or enter zero if you skipped Step 2.
Certificate Line 3. Any extra dollar amount you want withheld from each paycheck on top of what the allowances produce.

Line 3 is useful when you have side income the state isn’t already taxing at the source, such as freelance work, rental income, or investment gains. Adding a flat amount to each check can cover that liability without separate estimated payments.

When You Don’t Need to Fill Out the Worksheet

Two situations let you skip the allowance math entirely.

If you expect to owe no Illinois income tax this year and owed none last year, you can write “Exempt” on the designated line of the certificate instead of entering allowance numbers. Illinois ties this to the federal rule: you qualify only if you also qualified for full exemption on your federal Form W-4.⁴ Review it each year; if either condition stops being true, file a new IL-W-4 with actual allowances.

If you live in Iowa, Kentucky, Michigan, or Wisconsin and work in Illinois, a reciprocal agreement lets you have Illinois skip withholding so only your home state taxes your pay. Use Form IL-W-5-NR instead of the IL-W-4.⁵ You still owe tax to your home state.

When You Have to Redo the Form

You give the completed certificate to your employer’s payroll or HR office, not to the Department of Revenue. Cut the certificate off, hand it in, and keep the worksheet for yourself.¹

File a new IL-W-4 within 10 days if a change reduces the allowances you can claim, such as losing a dependent or a change in filing status after divorce.¹ When a change increases your allowances, such as a new child, no deadline applies, but filing a new form promptly means the larger exemption shows up in each paycheck instead of waiting until you file your return.

Adjusting the Numbers to Avoid Owing at Tax Time

Withholding that falls short of your actual liability by more than $1,000 can trigger a late-payment penalty and a requirement to make quarterly estimated payments going forward.¹ Interest accrues on unpaid balances, and the late-payment penalty rises from 2 percent to 10 percent once a payment is more than 30 days late.⁶

Two levers on the form let you build a cushion. Claim fewer allowances on the certificate than the worksheet says you’re entitled to. Or add a flat dollar figure on Line 3 of the certificate so an extra amount comes out of each check. Either move raises the tax withheld and reduces the chance of a bill in April.

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. What Is the Illinois Personal Exemption Allowance
3
Illinois Comptroller. Illinois State Income Tax Exemptions – 2026
4
Illinois General Assembly. Title 86 Revenue, Chapter I, Part 100 Income Tax, Section 100.7110 Withholding Exemption Certificate
5
Illinois Department of Revenue. IL-W-5-NR Employee’s Statement of Nonresidence in Illinois
6
Illinois Department of Revenue. Pub-103, Penalties and Interest for Illinois Taxes