CT-1

Adjusted Employer's Annual Railroad Retirement Tax Return or Claim for Refund

Agency
IRS
Revision
Rev. April 2025
Fillable fields
330
Pages
6
Official source
IRS form page
Checked
October 21, 2026
Fill CT-1 online
Page 1 of form CT-1

Form CT-1 X: Adjusted Employer's Annual Railroad Retirement Tax Return

Form CT-1 X is the Adjusted Employer's Annual Railroad Retirement Tax Return or Claim for Refund. The IRS About page says to use it to correct errors on a Form CT-1 previously filed. Form CT-1 is the Employer's Annual Railroad Retirement Tax Return.

The instructions say it corrects Tier 1 Employee tax, Tier 1 Employee Medicare tax, Tier 1 Employee Additional Medicare Tax and Tier 2 Employee tax, the matching Tier 1 and Tier 2 Employer taxes, and amounts reported for the credit for qualified sick and family leave compensation and the COBRA premium assistance credit. Each line has columns for the corrected amount, the amount originally reported, the difference and the tax correction.

The employer picks one of two processes: an adjusted railroad retirement tax return or a claim for refund or abatement. The form says to use a separate Form CT-1 X for each year that needs correction and to complete all five pages. This page has the April 2025 revision. The PDF can be filled out free in the browser on this page and downloaded without an account.

What's on Form CT-1 X

Header

EIN, RRB number, name as shown on the latest Form CT-1, address, the calendar year of the return being corrected and the date errors were discovered.

Part 1: Select ONLY one process

Line 1 for an adjusted railroad retirement tax return and line 2 for a claim for refund or abatement. The form says to check only one.

Part 2: Certifications

Line 3 certifies that Forms W-2 or W-2c have been or will be filed. Lines 4 and 5 hold certifications about repaying employees, employee consents or Employer RRTA taxes only, for overreported amounts.

Part 3: Corrections

Lines 6 to 40, each tied to a Form CT-1 line, covering Tier 1 and Tier 2 taxes on compensation and sick pay, tax adjustments and credits. Line 21 is a subtotal and line 26 the total.

Part 4: Explanation

Line 41 for corrections that include both underreported and overreported amounts, line 42 for reclassified workers, and line 43 for a detailed explanation of how the corrections were determined.

Part 5: Signature

The declaration, the signer's printed name, title, date and best daytime phone, and the Paid Preparer Use Only section.

How to fill out Form CT-1 X

  1. 1

    Header

    Enter the EIN, RRB number, name and address, the calendar year of the Form CT-1 being corrected and the date errors were discovered. The instructions say to repeat the name, EIN and year at the top of pages 2 to 5.

  2. 2

    Part 1

    Check line 1 for the adjustment process or line 2 for the claim process. The form says line 1 is checked when correcting both underreported and overreported amounts, and line 2 only when correcting overreported amounts.

  3. 3

    Part 2

    Check line 3. The form says to skip lines 4 and 5 when correcting underreported tax amounts only. For overreported amounts, check each box on line 4 or line 5 that applies.

  4. 4

    Part 3 columns

    For each line that changes, enter the corrected total in column 1, the amount originally reported or as previously corrected in column 2 and the difference in column 3. The instructions say to show a negative amount with a minus sign. Lines that don't apply stay blank.

  5. 5

    Line 26

    Combine lines 21 through 25c of column 4. The form says a positive amount is the amount owed, paid by the time the return is filed. A negative amount is credited to Form CT-1 under line 1, or refunded or abated under line 2.

  6. 6

    Parts 4 and 5

    Check lines 41 and 42 if they apply, explain each correction on line 43, then sign on page 5. The instructions say any later discovery dates and related errors are also reported on line 43.

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Deadlines, where to send it and payment

Underreported tax

The instructions say to file by the due date of the return for the return period in which the error was discovered and pay the amount owed by the time of filing.

Overreported tax

Under the adjustment process the instructions say to file more than 90 days before the period of limitations expires. A claim can be filed any time before it expires. In the last 90 days, only the claim process is available.

Period of limitations

The instructions say overreported taxes can generally be corrected within 3 years of the date Form CT-1 was filed or 2 years from the date the tax was paid, whichever is later, and underreported taxes within 3 years of filing.

Where to send it

The instructions list Department of the Treasury, Internal Revenue Service Center, Cincinnati, OH 45999-0007. A private delivery service uses Ogden-Internal Revenue Submission Processing Center, 1973 Rulon White Blvd., Ogden, UT 84201.

Not with Form CT-1

The form says not to attach it to Form CT-1 unless reclassifying workers. Errors only in the tax liabilities in Part II of Form CT-1 or on Form 945-A are not corrected on Form CT-1 X, the instructions say.

Paying an amount owed

The instructions say the amount on line 26 can be paid through EFTPS, the preferred method, or by check or money order payable to "United States Treasury."

Related forms

Who files Form CT-1 X?

  • Employers that filed Form CT-1

    The form says it is used to correct errors made on Form CT-1, Employer's Annual Railroad Retirement Tax Return, and the signature declares that an original Form CT-1 was filed.

  • Who signs for the employer

    The instructions list the owner of a sole proprietorship, a principal officer of a corporation, a responsible partner, member or officer of a partnership, and the fiduciary of a trust or estate. An authorized agent with a valid power of attorney may also sign.

  • Paid preparers

    The instructions say a paid preparer who isn't an employee of the filing entity signs Form CT-1 X and completes the Paid Preparer Use Only section, with a PTIN and the firm's name and EIN.

  • Not for other employment returns

    The instructions say not to use Form CT-1 X to correct Form 941, 941-SS, 943, 944 or 945, and point to Forms 941-X, 943-X, 944-X and 945-X instead.

  • Not for missing returns

    The instructions say that if a Form CT-1 wasn't filed for a year, Form CT-1 X is not used. Form CT-1 is filed for each of those years, with an exception on line 42 for reclassified workers.

Form CT-1 X is filed by the employer that filed Form CT-1. It is not a form railroad employees file.

Official sources and the blank

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Questions about Form CT-1

What is Form CT-1 X used for?

The About page says to use it to correct errors on a Form CT-1, Employer's Annual Railroad Retirement Tax Return, that was previously filed.

Can one Form CT-1 X fix several years?

No. The form says to use a separate Form CT-1 X for each year that needs correction.

What is the difference between line 1 and line 2?

Line 1 is the adjustment process, where a credit is applied to Form CT-1 for the period of filing. Line 2 is the claim process, used only for overreported amounts to ask for a refund or abatement.

Can Form CT-1 X request a refund of penalties or interest?

The instructions say to use Form 843, Claim for Refund and Request for Abatement, for assessed interest or penalties, not Form CT-1 or Form CT-1 X.

When is Form CT-1 treated as filed for the deadline?

The instructions say Form CT-1 is considered filed on the last day in February of the following year if it was filed before that date.

Can withheld Additional Medicare Tax be refunded on Form CT-1 X?

The instructions say a refund claim can't be filed to correct Tier 1 Employee Additional Medicare Tax actually withheld from employees.