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
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.