Illinois Form IL-W-4 – Employee’s Withholding Allowance Certificate & Estimator (2026)
Last reviewed: 2025-11-07
Use the Illinois Tax Form Calculator Form IL-W-4: Employee’s Illinois Withholding Allowance Certificate as a stand alone tax form calculator to quickly calculate specific amounts for your 2026 Illinois state tax return. Alternatively, you can use one of our Combined Federal and State Tax Estimators to quickly calculate your salary, tax, and take-home pay.
Form IL-W-4 tells your employer how much Illinois income tax to withhold from your paycheck. Illinois applies a flat 4.95% state income tax rate, so your withholding mainly depends on your gross pay, pay frequency, and any additional amount you request to be withheld, rather than complicated tax brackets. This page includes a quick withholding estimator to help you gauge how much tax is deducted each pay period and annually.
When to Review or Submit Form IL-W-4
Complete or update Form IL-W-4 when:
- You start a new job in Illinois, or you move and your employer changes.
- Your income or household situation changes (for example, you start or stop a second job, a spouse changes jobs, you receive large bonuses, or your retirement income changes).
- You want to increase or decrease additional withholding so you don’t owe at tax-time or get a large refund.
How to Use the IL-W-4 Withholding Estimator
Follow these steps to estimate your Illinois state withholding:
- Enter your gross pay per period (before retirement plan and federal tax withholdings).
- Select your pay frequency (monthly, biweekly, weekly) to annualize correctly.
- Enter any additional voluntary withholding you request on Line 3 of your IL-W-4.
- The calculator uses the Illinois flat rate of 4.95% to estimate your tax.
- The tool displays both your estimated tax per pay period and your annual withholding, helping you budget and plan effectively.
Note: While Illinois withholding amounts are derived from the rate and pay period, your employer still refers to Publication IL-700-T Withholding Tables for full payroll-period tables.
| 1 | Gross pay per period | |
| 2 | Number of pay periods per year (select frequency) | |
| 3 | Annual salary (Line 1 × Line 2) | |
| 4 | Illinois tax rate (fixed at 4.95% for 2026) | |
| 5 | Additional voluntary withholding | |
| 6 | Estimated Illinois tax per period ((Line 1 × Line 4) + Line 5) | |
| 7 | Estimated annual Illinois tax ((Line 6 × Line 2)) |
Example
Example: Alex earns $ 2,000 every two weeks and requests $ 20 extra withheld per paycheck. At the Illinois tax rate of 4.95%, the base withholding = $2,000 × 4.95% = $99.00. With the extra $20, each paycheck tax becomes $119. Over 26 biweekly pay periods that equals roughly $3,094 annually.
Why This Tool and Withholding Matter
- If you under-withhold, you may owe tax and interest when you file your Form IL-1040.
- If you consistently receive large refunds, you’re letting the state hold your money interest-free. Adjusting withholding frees up cash during the year.
- This estimator helps multi-job households, employees receiving commission/bonus pay, retirees earning Illinois-taxable pensions, and dual-filers align state withholding with actual liability.
Employers rely on your IL-W-4 to correctly apply withholding. Using this estimator improves transparency and helps ensure you’re neither under-nor over-withheld.
Last reviewed: 2025-11-07: If you believe this form requires an update, please contact us.
Related Forms and Resources
- Form IL-1040 – Individual Income Tax Return
- Form IL-1040-ES – Estimated Income Tax Payments
- Illinois DOR – Form IL-W-4
- Illinois DOR – Publication IL-700-T (Withholding Tables)
Quick Access Tools
Frequently Asked Questions
Will IL tax my Roth conversions?
Conversions are taxable federally and typically flow to IL; IL retirement exclusion usually applies to distributions, not conversions—check IL guidance.
How do I amend my Illinois return?
File Form IL-1040-X after your original IL-1040 is processed; include revised schedules (e.g., Schedule ICR/CR/M) and explanations.
Why does Illinois distinguish pre-1969 and post-1969 gains?
Because Illinois enacted its income tax on August 1, 1969, any appreciation before that date occurred before the state had authority to tax income. Form IL-F preserves fairness by taxing only the gain realized since Illinois income tax law took effect. This approach avoids retroactive taxation while ensuring current gains are taxed appropriately.
When should Schedule FD be filed?
File Schedule FD with your annual IL-1040 return for the tax year in which the deferred income became federally taxable.
Why is Schedule M important for accurate Illinois taxes?
Illinois uses Schedule M to ensure fairness in applying its flat 4.95% tax rate. Because Illinois starts from federal AGI, this form ensures only Illinois-approved income is taxed and proper deductions are applied. It’s especially vital for retirees, military personnel, and taxpayers with multistate investments.
Important Notes
All calculations are estimates for guidance only. Always review your return and consider professional advice when submitting official filings.