Illinois Form IL-1040 Calculator & Instructions
Last reviewed: 2025-11-03
Use the Illinois Tax Form Calculator Form IL-1040: Illinois Individual Income Tax Return 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.
This calculator uses Illinois' flat tax rate of 4.95% and the personal exemption allowance of $2,775 for tax year 2026. It is designed to mirror Form IL-1040 computations while keeping all thresholds and rates centrally updateable.
Enter your Illinois base income (which begins with your federal AGI plus Illinois adds and minus subtractions). Use whole dollars and apply rounding as directed. The personal exemption of $2,775 is applied after base income.
| Filing Status | Include Dependent? | ||
| Step 2 – Income | |||
| 1 | Federal adjusted gross income (Form 1040 Line 11) | ||
| 2 | Federally tax-exempt interest and dividends (Form 1040 Line 2a) | ||
| 3 | Other additions (Attach Schedule M) | ||
| 4 | Total income (Lines 1 + 2 + 3) | ||
| Step 3 – Base Income | |||
| 5 | Social Security benefits and retirement income (if included in Line 1) | ||
| 6 | Illinois income tax overpayment from federal Schedule 1 Line 1 | ||
| 7 | Other subtractions (Attach Schedule M) | ||
| 8 | Total subtractions (Lines 5 + 6 + 7) | ||
| 9 | Illinois base income (Line 4 − Line 8) | ||
| Step 4 – Exemptions | |||
| 10a | Exemption amount for yourself and spouse | ||
| 10b | Check if 65 or older: You Spouse | ||
| 10c | Check if legally blind: You Spouse | ||
| 10d | Dependents (Attach Schedule IL-E/EITC) | ||
| 10 | Total exemption allowance (Lines 10a–10d) | ||
| Step 5 – Net Income and Tax | |||
| 11 | Net income (Line 9 − Line 10 or Schedule NR) | ||
| 12 | Tax (Line 11 × 4.95% rate) | ||
| 13 | Recapture of investment credits (Attach Schedule 4255) | ||
| 14 | Income tax (Line 12 + Line 13) | ||
| Step 6 – Tax After Nonrefundable Credits | |||
| 15 | Tax paid to another state (Attach Schedule CR) | ||
| 16 | Property tax, K-12 education, volunteer credits (Attach Schedule ICR) | ||
| 17 | Credit from Schedule 1299-C | ||
| 18 | Total credits (Lines 15 + 16 + 17) | ||
| 19 | Tax after credits (Line 14 − Line 18) | ||
| Step 7 – Other Taxes | |||
| 20 | Household employment tax | ||
| 21 | Use tax on out-of-state purchases | ||
| 22 | Medical cannabis and gaming surcharges | ||
| 23 | Total tax (Lines 19 + 20 + 21 + 22) | ||
| Step 8 – Payments and Refundable Credits | |||
| 25 | Illinois income tax withheld (Attach Schedule IL-WIT) | ||
| 26 | Estimated payments and overpayments applied from prior year | ||
| 27 | Pass-through withholding (Attach Sch. K-1-P or K-1-T) | ||
| 28 | Pass-through entity tax credit (Attach Sch. K-1-P or K-1-T) | ||
| 29 | Earned Income Tax Credit (Attach Sch. IL-E/EITC) | ||
| 30 | Child Tax Credit (Attach Sch. IL-E/EITC) | ||
| 31 | Total payments and refundable credits (Lines 25–30) | ||
| Step 9 – Total | |||
| 32 | If Line 31 > Line 23 → overpayment (Line 31 − Line 23) | ||
| 33 | If Line 23 > Line 31 → tax due (Line 23 − Line 31) | ||
| Step 10 – Penalty and Donations | |||
| 34 | Underpayment penalty (Form IL-2210) | ||
| 35 | Voluntary charitable donations (Attach Schedule G) | ||
| 36 | Total penalty and donations (Lines 34 + 35) | ||
| Step 11 – Refund or Amount You Owe | |||
| 37 | Overpayment (Line 32 − Line 36 if > 0) | ||
| 38 | Refund amount (Line 37 portion to refund) | ||
| 40 | Credit forward (Line 37 − Line 38) | ||
| 41 | Amount you owe (Line 33 + Line 36 or as defined by Line 41 formula) | ||
The tax is computed by applying the flat rate of 4.95% to the base amount after exemption. This tool assumes no additional special credits or surtaxes unless you update the credit and deduction variables. Review the final line carefully before filing.
Last reviewed: 2025-11-03: If you believe this form requires an update, please contact us.
Update the $_v variables annually instead of changing calculator logic or layout. This keeps maintenance efficient and error-free for future years.
Quick Access Tools
Frequently Asked Questions
Do I need to file IL-1040-X if the IRS changes my income?
Yes. If the IRS adjusts your federal return and it affects Illinois tax, you must file IL-1040-X within 120 days of receiving the federal notice.
Are donations made through Schedule G-L tax-deductible?
Yes. Your Schedule G-L donations are eligible for a federal charitable deduction if you itemize on your federal Form 1040 Schedule A. Keep a copy of the filed schedule and any Lottery confirmation of your gift. The contribution will increase your Illinois payment or reduce your refund, but may lower your federal taxable income in the following year.
Changing jobs mid-year in IL
Update income/withholding and frequency; brackets are flat but credits/exemptions still matter.
Who must file Schedule FD?
You must file Schedule FD if you are a former Illinois resident who receives income (such as installment sale gains or deferred bonuses) sourced from Illinois that became taxable for federal purposes during 2026.
What documentation must accompany Schedule 1299-DA?
Attach copies of the other states’ filed tax returns, W-2s, or K-1s showing withholding and payments. Failure to attach proof can lead to denial of the credit. For convenience, you can track and upload copies directly through the MyTax Illinois portal.
Important Notes
All calculations are estimates for guidance only. Always review your return and consider professional advice when submitting official filings.