What IRS Form 1120X (2018) Is For

IRS Form 1120X, Amended U.S. Corporation Income Tax Return, is used by corporations to correct errors or make changes to a previously filed Form 1120 for the 2018 tax year (IRS About Form 1120-X). Corporations use this form to adjust income, deductions, credits, or make elections after the prescribed deadline.

When You’d Use Form 1120X for 2018 (Late or Amended Filing)

Corporations file Form 1120X for 2018 to fix errors like math mistakes, unreported income, incorrect deductions, or missing credits. It is also used to respond to IRS notices about discrepancies. Refund claims must meet the statute of limitations, generally within three years of the return’s due date or two years from when the tax was paid.

Key Rules Specific to 2018

• 2018 was the first year under the Tax Cuts and Jobs Act, with a flat 21% corporate tax rate.
  
  
• The corporate AMT was repealed, with AMT credits becoming refundable via Form 8827.
  
  
• Provisions introduced included BEAT (Base Erosion Minimum Tax), FDII (Foreign-Derived Intangible Income) deduction, and expanded cash method eligibility for corporations with $25 million or less in gross receipts.
  
  

Step-by-Step (High Level)

• Gather documentation: Obtain transcripts and original 2018 Form 1120 with supporting records.
• Complete Form 1120X: Show original amounts, corrected figures, and provide detailed explanations in Part II.
• Attach schedules: Include revised or new schedules, forms, and statements supporting amendments.
• File: Mail to the IRS center for your location or e-file if available.
• Maintain records: Keep copies of all filings and documents for at least three years.

Common Mistakes and How to Avoid Them

• Filing before the IRS processes the original return.
  
  
• Missing signatures or dates from corporate officers.
  
  
• Providing vague explanations like “error” instead of detailed reasoning.
  
  
• Confusing superseding with amended returns.
  
  
• Failing to pay additional tax owed promptly.
  
  
• Not verifying state requirements for corresponding amended returns.
  
  

What Happens After You File

The IRS generally processes amended returns in 8–12 weeks, though more complex cases may take longer. You’ll receive notices explaining adjustments, balances due, or refunds issued. If you owe additional tax, interest accrues from the original due date. Payment plans (Form 9465) or offers in compromise may apply, and appeal rights exist for disputed IRS adjustments.

FAQs

Can I still file an amended return for 2018?

Yes, you may file if within the statute of limitations. Refund claims must be submitted within three years of the original filing or two years of paying the tax, whichever is later. For most corporations, refund opportunities for 2018 expired in April 2022, but amendments can still correct liabilities.

What penalties apply to late-filed 2018 returns?

The penalty for late filing is 5% of unpaid tax per month, capped at 25%. Late payment penalties are 0.5% of unpaid tax per month. Interest accrues on both taxes and penalties from the original due date, making prompt filing and payment critical to limit growing balances (IRC Sections 6651 and 6601).

How do I get my 2018 tax transcripts?

You can request transcripts online at IRS.gov, call 800-908-9946, or file Form 4506-T by mail. Return transcripts show the actual return filed, while account transcripts display activity, payments, and adjustments. Using transcripts ensures accuracy in completing Form 1120X and avoids duplication or missing carryover amounts.

Is there a refund deadline for 2018 amendments?

Yes, refund claims are strictly time-limited. Corporations generally had until April 15, 2022, to file refund claims for 2018 returns filed by April 2019. Once the statute of limitations expires, refunds are barred, though amended filings are still necessary for correcting tax liability or maintaining compliance with federal requirements.

Do I need to amend my state return?

Most states require corporations to amend state tax filings if federal returns are amended. Each state sets its own deadlines and conformity rules, so check with your state tax agency. Failing to file amended state returns could result in mismatches, state-level penalties, or additional audits tied to IRS changes.

Can Form 1120X be e-filed?

Yes, many tax software providers support e-filing amended corporate returns. However, paper filing is still permitted, and some corporations may prefer mailing to the IRS. Always confirm that your filing software handles Form 1120X for 2018 before attempting to submit electronically, as not all providers support prior-year forms.

What if I discover another error after filing Form 1120X?

If you discover more errors after filing, you can submit another amended return. Each Form 1120X should cover all known errors at the time to avoid repeat processing delays. However, the IRS allows multiple amended filings for the same year if corrections are discovered later, with proper documentation attached.

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