Filing corporate taxes can be complicated, and sometimes corporations discover mistakes after submitting their returns. Form 1120-X exists to fix those errors. Whether you miscalculated income, forgot a deduction, or received corrected information from the IRS, this form allows you to set the record straight. Here's everything you need to know about Form 1120-X for the 2011 tax year.

What the Form Is For

Form 1120-X is the official IRS document that corporations use to correct errors on previously filed Form 1120 (U.S. Corporation Income Tax Return) or Form 1120-A returns. Think of it as the corporate version of an eraser—it lets you fix mistakes without starting from scratch. IRS.gov

Corporations use this form to:

• Correct mistakes on their original corporate tax return, such as incorrect income amounts, missed deductions, or mathematical errors
• Adjust previously filed returns that were later changed by the IRS through an audit or examination
• Claim additional refunds when the corporation overpaid taxes
• Pay additional taxes when the original return underreported tax liability
• Make certain elections after the normal deadline has passed, when regulations permit

The form uses a three-column format that clearly shows the original amounts, the changes being made, and the corrected totals—making it easy for both the corporation and the IRS to understand exactly what's being fixed.

When You’d Use Form 1120-X (Late/Amended Returns)

Understanding when to file Form 1120-X versus other correction methods is crucial for corporations.

File Form 1120-X when:

• You've already filed your original Form 1120 and the filing deadline has passed
• You discover errors after the IRS has processed your return
• You need to correct income, deductions, or credits that were reported incorrectly
• You receive corrected information from third parties (like amended K-1s from partnerships)
• The IRS audited your return and you're responding to adjustments

Don't confuse it with a superseding return: If you're still within your filing deadline (including extensions), you don't need Form 1120-X. Instead, you file a "superseding return"—simply filing a new, corrected Form 1120 that replaces the original. A superseding return is filed subsequent to the originally-filed return but within the filing period (including extensions). The superseding return becomes your official return, and you don't need the amendment form. IRS.gov

Important timing note: Form 1120-X must be filed only after the corporation has filed its original return. You cannot file an amended return before filing the original.

Key Rules or Details for 2011

For corporations amending their 2011 tax returns, several critical deadlines and rules apply:

Statute of Limitations (The Three-Year Rule): The most important rule is the filing deadline. Generally, Form 1120-X must be filed within 3 years after the date the corporation filed its original return, or within 2 years after the date the corporation paid the tax, whichever is later. A return filed before the due date is considered filed on the due date for statute purposes. IRS.gov

For 2011 corporate returns (typically due in 2012), this means:

• If your 2011 Form 1120 was originally due April 15, 2012, you generally had until April 15, 2015 to file an amended return
• If you filed with an extension on September 15, 2012, you had until September 15, 2015

Special exceptions extend this deadline:

• Net Operating Loss (NOL) carryback claims: Must be filed within 3 years after the due date (including extensions) of the return for the tax year of the NOL
• Bad debt or worthless security claims: Extended to 7 years after the due date of the return for the tax year the debt or security became worthless
• General business credit carrybacks: Follow the same 3-year rule as NOL carrybacks

These rules are established in section 6511 of the Internal Revenue Code, which governs limitations on credit or refund claims.

Filing requirements:

• Form 1120-X must be mailed—in 2011, electronic filing was not available for amended corporate returns
• The form must be signed by an authorized corporate officer (president, vice president, treasurer, or other officer authorized to sign)
• Supporting documentation must be attached, including revised schedules, statements, or forms that support the changes

Step-by-Step (High Level)

Step 1: Gather Your Documents

Collect your original Form 1120 (as filed or as adjusted by the IRS), all supporting schedules, and documentation supporting the changes you're making. You'll need these to complete the three-column comparison.

Step 2: Complete the Form Header

Enter your corporation's basic information: name, employer identification number (EIN), address, and the tax year being amended (ending month and year). Indicate which IRS Service Center received your original return.

Step 3: Fill Out Part I (Income and Deductions)

This three-column section is the heart of the form:

• Column (a): Enter amounts from your original return (or as adjusted by IRS)
• Column (b): Enter the net increase or decrease for each line—use parentheses for decreases
• Column (c): Calculate and enter the corrected amounts

Complete lines for total income, total deductions, taxable income, and total tax. Then enter your payments and credits to determine if you owe additional tax or are due a refund.

Step 4: Write Your Explanation in Part II

This is critical. For each line you changed in Part I, explain why you're making the change. Be specific—cite line numbers, provide calculations, and attach supporting documents. The clearer your explanation, the faster the IRS can process your amendment.

Step 5: Attach Supporting Documents

Include copies of any forms, schedules, or statements that support your changes. For example, if you're amending because of a changed depreciation deduction, attach a revised depreciation schedule. At the top of copies, write "Copy Only—Do Not Process."

If the corporation requests that the IRS electronically deposit a refund of $1 million or more, attach Form 8302, Electronic Deposit of Tax Refund of $1 Million or More.

Step 6: Sign and Date

An authorized corporate officer must sign and date the form. This includes the president, vice president, treasurer, assistant treasurer, chief accounting officer, or any other corporate officer (such as tax officer) authorized to sign. Unsigned forms will be rejected.

Step 7: Mail to the Correct IRS Service Center

Send Form 1120-X to the same IRS Service Center where you filed your original return. The instructions include a listing of addresses by region.

Step 8: Keep Copies

Retain copies of the complete amended return package for your records.

Common Mistakes and How to Avoid Them

Mistake #1: Filing Before the Original Return

You cannot amend a return that hasn't been filed yet. Wait until the IRS has received and processed your original Form 1120 before submitting Form 1120-X.

Mistake #2: Incomplete Explanation in Part II

Many corporations provide vague explanations like "error in calculation." Instead, be specific: "Line 1 - Gross receipts were understated by $50,000 due to omission of fourth quarter sales of $50,000 from ABC Customer. See attached corrected sales ledger."

Mistake #3: Forgetting to Recalculate Dependent Items

When you change one number, others may need adjustment. For example, changing gross income may affect:

• Charitable contribution limitations
• Dividends-received deduction calculations
• Section 179 expense limitations

The Form 1120-X instructions specifically note that deductions for such items as charitable contributions and the dividends-received deduction may have to be refigured because of changes made to items of income or expense.

Mistake #4: Not Attaching Supporting Documents

Claims for refunds or significant changes need documentation. Attach revised schedules, amended K-1s, or corrected 1099s that support your changes. Missing documentation causes processing delays.

Mistake #5: Using Form 1120-X for the Wrong Purpose

Don't use Form 1120-X to:

• Request a quick refund of estimated tax (use Form 4466, Corporation Application for Quick Refund of Overpayment of Estimated Tax instead)
• Obtain a tentative refund due to NOL carryback, net capital loss carryback, or unused general business credit carryback within one year (use Form 1139, Corporation Application for Tentative Refund instead)
• Change accounting methods (use Form 3115, Application for Change in Accounting Method instead)

Mistake #6: Mathematical Errors in Column (c)

Column (c) must equal column (a) plus (or minus) column (b). Double-check all calculations, as errors here delay processing. Amounts entered on lines 1 through 4 in column (c) must equal the amounts that would be entered on the applicable lines of the tax return if all adjustments and corrections were taken into account.

Mistake #7: Missing Signature

Unsigned returns are invalid. Ensure an authorized officer signs and dates the form.

What Happens After You File

Once you mail Form 1120-X, patience is required—the process takes considerably longer than filing original returns.

Processing Timeline

According to the Form 1120-X instructions, it often takes 3 to 4 months to process the form. This timeframe applies to amendments filed during the 2011 tax year period. IRS.gov

What the IRS Does

• Receipt and routing: The IRS Service Center receives your form and routes it to the Accounts Management division
• Review: An IRS examiner reviews your amendment, checking calculations and verifying explanations
• Verification: The IRS may compare your amended return against the original and check for consistency
• Correspondence: If the IRS needs clarification or additional documentation, they'll send a letter to the address on your return

Possible Outcomes

If you're claiming a refund:

• The IRS will process your refund separately from any refund claimed on your original return
• The IRS will figure any interest due and include it in the refund
• The refund is mailed to your corporation's address or can be directly deposited (for refunds of $1 million or more, Form 8302 is required)
• Line 11 on Form 1120-X will show only the additional amount of overpayment—this additional amount will be refunded separately from the amount claimed on the original return

If you owe additional tax:

• Payment should be submitted with Form 1120-X to minimize interest charges
• If the corporation does not use electronic funds transfers, including the Electronic Federal Tax Payment System (EFTPS), enclose a check and make it payable to the "United States Treasury"
• Interest accrues from the original due date of the return

If the IRS disagrees:

• You'll receive a notice explaining the disagreement
• You have the right to respond with additional information or appeal the decision

Estimated Tax Credits

If you choose to credit part or all of any overpayment to the next year's estimated tax, enter the amount on line 12 along with the tax period. No interest will be paid on this amount, and the election to apply part or all of the overpayment to the next year's estimated tax is irrevocable.

State Returns

If your federal amendment affects your state tax liability, you may need to file amended state returns as well. Check your state's requirements.

FAQs

Q1: Can I e-file Form 1120-X for my 2011 tax year?

No. For the 2011 tax year, Form 1120-X had to be filed by mail. Electronic filing of amended corporate returns became available in later years through the Modernized e-File (MeF) system, but was not an option for 2011 amendments. IRS.gov

Q2: What if I miss the three-year deadline?

Generally, if you miss the statute of limitations, you cannot claim a refund. The IRS statute of limitations for claiming refunds is governed by section 6511. However, you may still file an amended return to correct underreported income to avoid penalties if the IRS discovers the error later. Certain exceptions (like the 7-year rule for bad debts) may apply in specific situations. IRS.gov

Q3: Should I file Form 1120-X if the IRS already sent me a notice about an error?

It depends. The IRS may correct certain errors automatically, such as mathematical errors. If the IRS corrected a simple mathematical error, you typically don't need to file Form 1120-X—the IRS has already adjusted your account. However, if you disagree with an IRS adjustment from an examination, you would respond to that notice directly, not by filing Form 1120-X.

Q4: Can I amend an amended return?

Yes. If you discover another error after filing Form 1120-X, you can file another Form 1120-X. Form 1120-X is used to correct Form 1120 as originally filed, or as later adjusted by an amended return, a claim for refund, or an examination. The second amendment should reflect the amounts from the first amended return in column (a), not the original return amounts. IRS.gov

Q5: What if I'm amending multiple years?

File a separate Form 1120-X for each tax year being amended. Each year is a separate return and must be filed individually. Clearly mark the tax year on each form in the space above the employer identification number by entering the ending month and year.

Q6: Do I need to attach my original return to Form 1120-X?

No, do not attach your entire original return. However, if Form 1120-X is used as a carryback claim, attach copies of Form 1120 (or Form 1120-A, if applicable), pages 1 and the tax computation page, for both the year the loss or credit originated and for the carryback year. Also attach any other forms, schedules, or statements that are necessary to support the claim. At the top of the forms or schedules attached, write "Copy Only—Do Not Process."

Q7: What if my amendment involves a reportable transaction?

If the corporation's return is being amended for a tax year in which the corporation participated in a "reportable transaction," attach Form 8886, Reportable Transaction Disclosure Statement. If a reportable transaction results in a loss or credit carried back to a prior tax year, attach Form 8886 for the carryback years. IRS.gov

Additional Resources

• IRS Form 1120-X Information
• Amended and Superseding Corporate Returns Guidance
• Publication 542 - Corporations
• Statute of Limitations Information

This guide provides general information about Form 1120-X for the 2011 tax year based on official IRS sources. Tax situations vary, and corporations with complex amendments should consult with qualified tax professionals to ensure compliance with all applicable rules and regulations.