Printable Form 2026

IRS Instruction CT-1X – IRS Forms, Instructions, Pubs 2026

IRS Instruction CT-1X – IRS Forms, Instructions, Pubs 2026 – If you’re a railroad employer and you’ve discovered an error on a previously filed Form CT-1 (Employer’s Annual Railroad Retirement Tax Return), or you need to claim a refund for overpaid railroad retirement taxes, Form CT-1X is the required IRS form. The latest official instructions (Rev. April 2025) provide clear guidance on correcting Tier 1 and Tier 2 taxes, Medicare taxes, Additional Medicare Tax, and remaining COVID-era credits.

This SEO-optimized guide summarizes the most current IRS Instructions for Form CT-1X directly from irs.gov. It walks you through who must file, deadlines, the adjustment vs. claim process, line-by-line instructions, and tips to avoid penalties. Always download the latest PDF from the IRS for your specific situation: Instructions for Form CT-1X (PDF).

What Is Form CT-1X?

Form CT-1X is the “Adjusted Employer’s Annual Railroad Retirement Tax Return or Claim for Refund.” Railroad employers use it to:

  • Correct underreported or overreported Tier 1 Employer/Employee taxes, Tier 2 taxes, Tier 1 Medicare taxes, and Additional Medicare Tax.
  • Adjust or claim credits for qualified sick and family leave compensation (leave taken after March 31, 2020, and before October 1, 2021).
  • Claim the COBRA premium assistance credit (for coverage periods beginning April 1, 2021, through September 30, 2021).
  • Make interest-free adjustments under IRC sections 6205 and 6413 or request refunds/abatements under sections 6402, 6414, and 6404.

Important: File a separate Form CT-1X for each tax year you are correcting. Do not attach it to your current Form CT-1 unless you are reclassifying workers.

Who Must File Form CT-1X?

Railroad employers who filed Form CT-1 for a prior year and now need to correct it. Common scenarios include:

  • Errors in compensation, tips, or sick pay reporting.
  • Miscalculated taxes or credits.
  • Worker reclassification (attach to a delinquent Form CT-1).
  • Overpaid taxes eligible for refund.

Do not use Form CT-1X if you never filed a Form CT-1 for the year—file the original Form CT-1 instead.

When to File Form CT-1X (Deadlines & Period of Limitations)?

File as soon as you discover the error. Timing affects penalties and interest:

  • Underreported taxes → File by the due date of the Form CT-1 for the year you discovered the error and pay the balance to qualify for interest-free treatment.
  • Overreported taxes → Use the adjustment process (credit to your current Form CT-1) as soon as possible (but more than 90 days before the limitations period expires) or the claim process for a direct refund.

Limitations periods (generally):

  • 3 years from the date you filed Form CT-1 (or the last day of February if filed early).
  • For overpayments: Also 2 years from the date you paid the tax.

Many lines related to 2020–2021 deferred taxes and certain employee retention/leave credits are now reserved because the limitations periods expired (February 2024 for most 2020 items; February 2025 for 2021). Check the instructions for your specific year.

Adjustment Process vs. Claim Process (Part 1)

Choose only one:

  • Line 1 – Adjusted Return (recommended for most cases): Use if you have any underreported amounts or want to apply an overpayment as a credit to your current Form CT-1. The net amount on line 26 (if negative) becomes a credit.
  • Line 2 – Claim: Use only if you have overreported amounts only and want a refund or abatement. You cannot use this if any underreported tax appears on the form.

Pro tip: Treat underreported credits like overreported taxes (and vice versa) when deciding.

Step-by-Step: How to Complete Form CT-1X?

The form has 5 parts. Complete all five pages.

Part 2: Certifications (Lines 3–5)

  • Line 3: Certify that you have filed (or will file) correct Forms W-2/W-2c with the SSA.
  • For overreported amounts (lines 4 or 5): You must check at least one box confirming you repaid/reimbursed employees, obtained written statements or consents (per Rev. Proc. 2017-28), or that the adjustment/claim is only for employer taxes or unwithheld amounts. Keep records for 4–6 years—do not send them to the IRS.

Part 3: Corrections (Lines 6–41)

Use four columns:

  • Column 1 — Corrected total (all employees)
  • Column 2 — Originally reported (or as previously corrected)
  • Column 3 — Difference (use minus sign for negative)
  • Column 4 — Tax correction (multiply column 3 by the applicable rate)

Key lines include:

  • Lines 6–17: Tier 1/Tier 2 employer and employee taxes on compensation and sick pay.
  • Line 11/17: Additional Medicare Tax — Special rules apply (correct compensation for administrative errors; explain on line 43).
  • Line 18: Tax adjustments from prior Form CT-1.
  • Lines 19, 20b, 20c: Nonrefundable portions of leave and COBRA credits (use Worksheets 1–3).
  • Lines 24, 25b, 25c: Refundable portions.
  • Lines 27–30, 33–38: Qualified compensation, health plan expenses, and collectively bargained amounts (enter differences only; feed into worksheets).

Line 26 = Total correction. Positive = you owe; negative = credit/refund.

Line 41: Check if your corrections include both under- and overreported amounts.

Line 42: Check if reclassifying workers (provide details on line 43).

Part 4: Explanations (Line 43)

This is critical. Clearly explain every correction:

  • Which line(s) are affected
  • Date discovered
  • Amount of the error
  • Reason (e.g., “Misclassified independent contractor as employee – discovered during 2025 audit”)

Insufficient explanations delay processing.

Part 5: Signature

An authorized person (owner, corporate officer, etc.) must sign. Paid preparers must provide PTIN and sign.

Worksheets for Credits (2020–2021 Leave & COBRA)?

If you are adjusting or claiming leave or COBRA credits, complete:

  • Worksheet 1 — Qualified sick/family leave (March 31, 2020 – March 31, 2021)
  • Worksheet 2 — Qualified sick/family leave (April 1, 2021 – September 30, 2021)
  • Worksheet 3 — COBRA premium assistance

These worksheets calculate nonrefundable and refundable portions after applying limits, exclusions under section 3231(e)(1), and other credits.

Where to File Form CT-1X?

Mail to: Department of the Treasury
Internal Revenue Service Center
Cincinnati, OH 45999-0007

Private Delivery Service: Ogden – Internal Revenue Submission Processing Center
1973 Rulon White Blvd.
Ogden, UT 84201

Penalties and Interest

  • Timely filed and paid underreported amounts → No failure-to-pay (FTP), failure-to-deposit (FTD), or interest penalties (with proper discovery date and explanation).
  • Late or incomplete → Penalties apply. Attach an amended Form 945-A if needed to avoid averaged FTD penalties.

Common Mistakes to Avoid

  • Using the wrong process (adjustment vs. claim).
  • Forgetting to explain corrections on line 43.
  • Incorrectly handling Additional Medicare Tax.
  • Missing W-2/W-2c certification.
  • Filing after the limitations period has expired.

Additional Resources

Disclaimer: This article summarizes the April 2025 IRS Instructions for Form CT-1X for informational purposes only. Tax rules are complex and subject to change. Consult a qualified tax professional or the IRS directly for advice specific to your situation. The IRS website is the authoritative source.

Visual example of related railroad retirement tax forms and liability summaries (Form CT-1 context).

Filing Form CT-1X correctly can save you money, avoid audits, and keep your railroad business compliant. Bookmark this guide and check IRS.gov/CT1X for any future developments. If you found this helpful, share it with other railroad employers!

Last updated: February 2026 based on Rev. April 2025 instructions.