IL-1120-X

A complete, line-by-line guide to filing Illinois Form IL-1120-X (R-12/24) and assembling every required attachment.

Form IL-1120-X is the Illinois Department of Revenue’s amended return for C-corporations to correct a previously filed Illinois Corporation Income and Replacement Tax return. Use it only for tax years ending on or after December 31, 2024; earlier tax years require a different form. The first panel (page 1) asks you to specify the tax year beginning and ending dates you’re amending, identify your corporation, and disclose whether your change stems from state or federal adjustments. You may also signal unitary/foreign-insurer status, special elections (such as treating all nonbusiness income as business income when filing by the extended due date), and technical items (e.g., Schedule 80/20, IL-4562, 1299-D). If the amended calculation results in tax due (Line 68), you include payment using Form IL-1120-X-V and mail everything to the department’s P.O. Box listed on the form. The core of the return (pages 2–3) has two columns—Column A (“as most recently reported or adjusted”) and Column B (“corrected amount”)—so you can show the before/after numbers for income, subtractions, apportionment, tax, credits, payments, and refund/balance due. Page 4 is a supporting-documents roadmap telling you exactly what to attach for each box or line you complete; missing attachments can cause the department to disallow the item.

How To File IL-1120-X

  1. Confirm You’re Using The Right Year. Use IL-1120-X for tax years ending on or after 12/31/2024; otherwise follow the instructions to find the correct prior-year form. (See the top banner on page 1.)
  2. Prepare Your Schedules And Federal Proof. If your change is due to federal action, check the federal-change box, indicate “partial agreed” or “finalized,” enter the finalization date, and attach the federal finalization (e.g., IRS report or transcript). Attach any Illinois schedules you check in Step 1 (UB, Subgroup, 1299-D, IL-4562, M, 80/20, etc.). See the attachments checklist on page 4.
  3. Compute The Amended Amounts. Complete Columns A and B throughout Steps 2–8; use whole dollars.
  4. Pay If You Owe. If Line 68 shows tax due, complete Form IL-1120-X-V, write the FEIN, tax-year ending, and “IL-1120-X-V” on your check or money order payable to Illinois Department of Revenue, and attach voucher and payment to page 1. Also enter the amount you are paying in the box at the top of page 1.
  5. Mail Your Amended Return. Send the signed return (and payment if due) to: Illinois Department of Revenue, P.O. Box 19016, Springfield, IL 62794-9016 (see the footer on page 1).
How To Complete IL-1120-X

How To Complete IL-1120-X

Before You Start — Tax Year You Are Amending (Page 1 Top Banner)

  • Tax Year Beginning / Ending (Month/Day/Year): Enter the exact start and end dates of the tax year you are amending. If the year ended before 12/31/2024, do not use this version.

Step 1: Identify Your Corporation (Page 1)

  • A — Name (Check If Name Change): Enter the complete legal business name. If it changed since the original filing, check the box.
  • B — Mailing Address: If applicable, add C/O, then street/PO Box, City, State, ZIP.
  • C — Business Type Boxes: Check if you are a Unitary Filer (Combined return) or a Foreign insurer; follow the instructions and attach required schedules (see page 4).
  • D — Increased Net Loss Only: Check if this filing is solely to report an increased net loss on Line 37, Column B.
  • E — Federal Disclosures: Check if you completed Federal Form 8886 or Federal Schedule M-3, Part II, Line 12; attach those forms if not previously provided.
  • F — Illinois Schedule UB: Check if attached.
  • G — Subgroup Schedule: Check if attached.
  • H — Illinois Schedule 1299-D: Check if attached.
  • I — Form IL-4562: Check if attached.
  • J — Illinois Schedule M (For Businesses): Check if attached.
  • K — Schedule 80/20: Check if attached.
  • L — 52/53-Week Filer: Check if applicable.
  • Top-Right Box — “Enter The Amount You Are Paying”: If Line 68 will be paid with the return, enter the payment amount here (whole dollars). Attach payment with Form IL-1120-X-V to page 1.
  • M — FEIN: Enter the Federal Employer Identification Number.
  • N — NAICS Code: Enter your NAICS code (see instructions).
  • O — Illinois Corporate File (Charter) Number: Enter your state corporate number.
  • P — Type Of Change: Check NLD, State change, or Federal change. If federal, also check Partial agreed or Finalized, enter the finalization date, and attach your federal finalization.
  • Q — Election To Treat All Nonbusiness Income As Business Income: Check if you are filing on or before the extended due date and making this election.
  • R — Discharge Of Indebtedness Adjustment: Check if you made this adjustment on Schedule NLD/UB-NLD or Line 36; attach federal Form 982.
  • S — Schedule INL: Check if attached.
  • T — Annualized Income (Form IL-2220): Check if you annualized on IL-2220.
  • U — Public Law 86-272 Protection: Check if your business activity is protected under PL 86-272.
  • V — Throwback Adjustment: Check if applicable (see instructions).
  • W — Double Throwback Adjustment: Check if applicable (see instructions).
  • Explain The Changes: Use the lined area to clearly describe what changed and why; attach extra pages if needed.
  • Where To Mail / Payment Reminder: If Line 68 is tax due, complete IL-1120-X-V, write FEIN + tax-year ending + “IL-1120-X-V” on your check/money order to Illinois Department of Revenue, attach to page 1, and mail the return to P.O. Box 19016, Springfield, IL 62794-9016.

Step 2: Figure Your Income Or Loss (Page 2 — Columns A & B)

  1. Federal Taxable Income (from federal Form 1120).
  2. Federal NOL Deduction (from federal Form 1120).
  3. State/Municipal/Other Interest excluded from Line 1.
  4. Illinois Income & Replacement Tax/Surcharge deducted in reaching Line 1.
  5. Illinois Special Depreciation — Addition (attach IL-4562).
  6. Related-Party Expenses — Addition (attach Schedule 80/20).
  7. Distributive Share Of Additions (attach K-1-P or K-1-T).
  8. Other Additions (attach Schedule M).
  9. Total Income Or Loss = add Lines 1–8.

Step 3: Figure Your Base Income Or Loss (Page 2)

  1. U.S. Treasury / Exempt Federal Interest (subtraction).
    11–15. River Edge / High Impact / Contribution subtractions (attach Schedule 1299-B).
  2. Contributions To Certain Job Training Projects (subtraction).
  3. Foreign Dividend Subtraction (attach Schedule J).
  4. Illinois Special Depreciation — Subtraction (attach IL-4562).
  5. Related-Party Expenses — Subtraction (attach 80/20).
  6. Distributive Share Of Subtractions (attach K-1-P or K-1-T).
  7. Other Subtractions (attach Schedule M).
  8. Total Subtractions = add Lines 10–21.
  9. Base Income Or Loss = Line 9 − Line 22.
    Checkbox A/B (Stop Box):
  • A: If all Line 23 is from inside Illinois, check A and carry Line 23 directly to Step 5, Line 35; skip Step 4 (leave Lines 24–34 blank). Unitary filers must not choose A—use B.
  • B: If any income is from outside Illinois or you are unitary, check B and complete Step 4 (do not leave Lines 28–30 blank).

Step 4: Figure Your Income Allocable To Illinois (Page 2 — Complete Only If You Checked B)

  1. Nonbusiness Income/Loss (attach Schedule NB).
  2. Business Income/Loss Included In Line 23 From Non-Unitary Partnerships, Partnerships On Schedule UB, S Corps, Trusts, Estates.
  3. Add Lines 24 + 25.
  4. Business Income/Loss = Line 23 − Line 26.
  5. Total Sales Everywhere (cannot be negative).
  6. Total Sales Inside Illinois (cannot be negative).
  7. Apportionment Factor = Line 29 ÷ Line 28 (six decimals).
  8. Business Income/Loss Apportionable To Illinois = Line 27 × Line 30.
  9. Nonbusiness Income/Loss Allocable To Illinois (attach Schedule NB).
  10. Business Income/Loss Apportionable To Illinois From Pass-Throughs Listed In Line 25.
  11. Base Income Or Loss Allocable To Illinois = add Lines 31–33.

Step 5: Figure Your Net Income (Page 3)

  1. Base Income Or Net Loss (from Step 3, Line 23 or Step 4, Line 34).
  2. Discharge Of Indebtedness Adjustment (attach federal Form 982).
  3. Adjusted Base Income Or Net Loss = Line 35 + Line 36.
  4. Illinois Net Loss Deduction (attach Schedule NLD or UB/NLD). If Line 37 ≤ 0, enter 0. Check the box and attach details if you merged losses.
  5. Net Income = Line 37 − Line 38.

Step 6: Figure Your Replacement Tax After Credits (Page 3)

  1. Replacement Tax = Line 39 × 2.5%.
  2. Recapture Of Investment Credits (attach Schedule 4255).
  3. Replacement Tax Before Credits = Line 40 + Line 41.
  4. Investment Credits (attach Form IL-477).
  5. Replacement Tax After Credits = Line 42 − Line 43 (if <0, enter 0).

Step 7: Figure Your Income Tax After Credits (Page 3)

  1. Income Tax = Line 39 × 7.0%.
  2. Recapture Of Investment Credits (attach Schedule 4255).
  3. Income Tax Before Credits = Line 45 + Line 46.
  4. Income Tax Credits (attach Schedule 1299-D).
  5. Income Tax After Credits = Line 47 − Line 48 (if <0, enter 0).

Step 8: Figure Your Refund Or Balance Due (Page 3)

  1. Replacement Tax Before Reductions (carry from Line 44).
  2. Foreign Insurer Replacement-Tax Reduction (attach Schedule INS or UB/INS).
  3. Net Replacement Tax = Line 50 − Line 51.
  4. Net Income Tax Before Reductions (carry from Line 49).
  5. Foreign Insurer Income-Tax Reduction (attach Schedule INS or UB/INS).
  6. Net Income Tax = Line 53 − Line 54.
  7. Medical Cannabis Surcharge (per statute).
  8. Gaming Licensee Asset-Sale Surcharge (per statute).
  9. Total Taxes & Surcharges = Lines 52 + 55 + 56 + 57.
  10. Payments (a–e):
  • 59a Prior overpayment credits applied to this year.
  • 59b All payments made before filing this amended return.
  • 59c Pass-through withholding reported to you (attach K-1-P / K-1-T).
  • 59d Pass-through entity tax credit reported to you (attach K-1-P / K-1-T).
  • 59e Illinois income tax withholding (attach Form(s) W-2G).
  1. Total Payments = add 59a–59e.
  2. Previously Paid Penalty & Interest (for this year).
  3. Total Overpayment Issued/Carried Forward Before This Amended Return (see instructions).
  4. Add Lines 61 + 62.
  5. Net Tax Paid = Line 60 − Line 63.
  6. Overpayment (if Line 64 > Line 58) = Line 64 − Line 58.
  7. Credit Forward portion of Line 65 (check box and attach statement if credit goes to a different FEIN).
  8. Refund = Line 65 − Line 66.
  9. Tax Due With This Amended Return (if Line 58 > Line 64) = Line 58 − Line 64. You’ll be billed separately for any additional penalty and interest.

Step 9: Sign Below (Page 3)

  • Authorized Officer: Sign, date (MM/DD/YYYY), enter title and phone; check the box to allow the department to discuss with your paid preparer.
  • Paid Preparer: Print/type name, PTIN, signature, date, and check self-employed if applicable; include firm name, FEIN, address, and phone.

Attachments Checklist (Page 4)

Use page 4 as your attach-what-you-claim guide. Examples:

  • Federal items: If you checked federal change (Step 1, P) or completed Form 8886/Schedule M-3 (Step 1, E), attach those federal forms; if Line 1 changed due to federal action, attach federal finalization (e.g., refund check copy, IRS report, transcript).
  • Schedules tied to lines: IL-4562 (Lines 5/18), 80/20 (Lines 6/19), K-1-P/K-1-T (Lines 7/20, 25/33, 59c/59d), Schedule M (Lines 8/21), 1299-B (Lines 11–15), Schedule J (Line 17), Schedule NB (Lines 24/32), NLD or UB/NLD (Line 38), IL-477 (Line 43), 1299-D (Line 48), INS or UB/INS (Lines 51/54), W-2G (Line 59e).
  • Unitary/Foreign insurer filers: Attach Schedule UB/Subgroup and, if foreign insurer, Schedule INS/UB-INS as indicated.
    Important: The form warns that failing to attach required documents may lead to disallowance of the related item.

Attachment Notes

Attach the items below with your IL-1120-X. If a note tells you to “check the box” for a schedule, that refers to the checkbox in Step 1 of page 1.

  • Base Form: If you are filing Form IL-1120-X, include federal Form 1120-X and, when applicable, federal Form 1139 or the federal RAR.
  • Step 1, Line C — Unitary Only: Attach Schedule UB/Subgroup Schedule and mark the Step 1, Lines F/G boxes.
  • Step 1, Line C — Foreign Insurer Only: Attach Schedule INS.
  • Step 1, Line C — Unitary & Foreign Insurer: Attach Schedule UB/Subgroup and Schedule UB/INS; also check Step 1, Lines F/G.
  • Step 1, Line E: Attach Federal Form 8886 or Federal Schedule M-3 (as applicable).
  • Step 1, Line R: Attach Federal Form 982.
  • Step 1, Line S: Attach Schedule INL.
  • Step 1, Line T: Attach Form IL-2220.
  • Line 1 (If Changed): Include federal finalization proof—e.g., refund check copy, IRS audit report, or federal transcript verifying federal taxable income.
  • Lines 5 & 18: Attach Form IL-4562 and check Step 1, Line I.
  • Lines 6 & 19: Attach Schedule 80/20 and check Step 1, Line K.
  • Lines 7 & 20: Attach Schedules K-1-P or K-1-T.
  • Lines 8 & 21: Attach Schedule M plus any support it lists and check Step 1, Line J.
  • Lines 11–15: Attach Schedule 1299-B plus any support it lists.
  • Line 17: Attach Illinois Schedule J and federal Form 1120, Schedule C (or equivalent).
  • Lines 24 & 32: Attach Schedule NB.
  • Lines 25 & 33: Attach Schedules K-1-P or K-1-T (for the pass-throughs listed).
  • Lines 28–30 (If Changed): Attach all relevant out-of-state returns.
  • Line 36: Attach Federal Form 982 and (as flagged earlier) ensure Step 1, Line R is checked.
  • Line 38: Attach Schedule NLD or UB/NLD (unitary filers).
  • Lines 41 & 46: Attach Schedule 4255 (recapture of investment credits).
  • Line 43: Attach Form IL-477 plus any support it lists.
  • Line 48: Attach Schedule 1299-D plus support required in the 1299-D instructions or Schedule 1299-I, and check Step 1, Line H.
  • Lines 51 & 54: For foreign-insurer reductions, attach Schedule INS or Schedule UB/INS (unitary filers) and ensure Step 1, Line C is checked.
  • Line 59c: Attach all Schedules K-1-P and K-1-T showing pass-through withholding.
  • Line 59d: Attach all Schedules K-1-P and K-1-T showing pass-through entity tax credit.
  • Line 59e: Attach copies of all Forms W-2G.
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