IRS Form CT-1X – Adjusted Employer’s Annual Railroad Retirement Tax Return or Claim for Refund – Railroad employers face unique tax obligations under the Railroad Retirement Tax Act (RRTA), funding benefits for over 30,000 retirees through Tier 1 and Tier 2 payroll taxes. But errors in reporting compensation or withholding can lead to under- or overpayments, requiring corrections to avoid penalties up to 25% of unpaid taxes. IRS Form CT-1X—the Adjusted Employer’s Annual Railroad Retirement Tax Return or Claim for Refund—is your tool for fixing these issues on previously filed Form CT-1 returns. For 2025, with Tier 1 wages capped at $176,100 and Tier 2 at $130,800, timely adjustments ensure compliance amid rising earnings limits. This SEO-optimized guide, based on the April 2025 revision (Catalog No. 20339E), covers filing requirements, deadlines, and strategies to minimize liabilities for railroad employers.

What Is IRS Form CT-1X?
IRS Form CT-1X is used to correct errors on Form CT-1, the Employer’s Annual Railroad Retirement Tax Return, or to claim refunds for overreported taxes. It adjusts Tier 1 (Social Security-equivalent) and Tier 2 taxes, including employee withholdings and employer shares, under Chapters 21 and 22 of the Internal Revenue Code. Unlike Form CT-1, which reports annual RRTA liabilities, CT-1X handles corrections like misreported compensation or deposit shortfalls.
Key features:
- Adjustment vs. Refund: Use the adjustment process (faster, no refund check) for overpayments; claim refunds for larger amounts.
- Tier 1/Tier 2 Corrections: Covers retirement (6.2%), Medicare (1.45%), and supplemental Tier 2 rates (4.9% employee, 13.1% employer in 2025).
- No COVID Deferrals: The April 2025 revision removes lines for 2020-2021 deferrals, as limitations expired February 28, 2025.
Download the form and instructions from IRS.gov/FormCT1X for the latest PDF.
Who Needs to File IRS Form CT-1X in 2025?
Railroad employers who filed Form CT-1 for 2024 (due February 28, 2025) must use CT-1X to correct discovered errors, such as underreported wages or overwithheld taxes. Filing is required if adjustments affect total tax liability; no filing if errors don’t change taxes.
| Scenario | Filing Required? | Details |
|---|---|---|
| Underreported Compensation | Yes | Correct Tier 1/Tier 2 taxes; pay additional by discovery date’s due date (e.g., March 2, 2026, for 2025 discoveries). |
| Overreported Withholding | Yes | Claim refund or adjustment; certify no W-2c needed if SSA-corrected. |
| Deposit Shortfalls | Yes | Adjust via Form 945-A; semiweekly depositors deposit by 15th of following month. |
| No Tax Change | No | E.g., offsetting errors; document internally. |
| Third-Party Sick Pay | Yes | Coordinate with Forms W-2/W-3c for consistency. |
Use EIN; third-party payers file separately. Consult Pub. 15 (Circular E) for RRTA specifics.
Filing Deadlines and Extensions for Form CT-1X
No fixed deadline—file within the statute of limitations (3 years from CT-1 due date or 2 years from tax payment). For 2024 CT-1 errors discovered in 2025, file by March 2, 2026, to avoid interest.
- Payment Due: Additional tax by original CT-1 due date or discovery date’s equivalent (e.g., February 28, 2026, for 2025 errors).
- Refunds: Claim within 3 years; adjustments anytime before limitations expire.
- Extensions: Request via Form 8809 (up to 30 days automatic); pay estimates to halt interest (0.5%/month).
- Where to File: Mail to Department of the Treasury, Internal Revenue Service Center, Kansas City, MO 64999-0005 (no e-file; paper only).
For semiweekly depositors, makeup shortfalls by the 15th of the next month.
Step-by-Step Guide to Completing IRS Form CT-1X
Gather original CT-1, payroll records, and W-2s. Use the April 2025 form; explain changes in Part III.
- Line 1: Adjustment Election – Check for overpayment adjustment (faster) or refund claim.
- Header: EIN, name, address; tax year (e.g., 2024).
- Part I: Employee Taxes – Correct Tier 1 (lines 2-5), Medicare (6-9), Tier 2 (10-13); show original vs. corrected amounts.
- Part II: Employer Taxes – Mirror employee corrections for matching shares.
- Line 21: Total Correction – Net over/underpayment.
- Line 26: Balance Due/Refund – Pay or claim; attach Form 945-A if semiweekly.
- Part III: Explanation – Detail errors (e.g., “Underreported $1,000 wages”); certify lines 4/5 for withholding protection.
- Sign & Attach: Officer signs; include W-2c copies if filed.
Example: Underreported $1,000 RRTA wages in 2024—add $76.50 Tier 1 ($1,000 × 7.65%) on lines 2/3; pay by March 2, 2026.
2025 RRTA Tax Rates and Adjustments on Form CT-1X
Rates unchanged: Tier 1 mirrors FICA (7.65% total), Tier 2 at 4.9% employee/13.1% employer. Adjustments recalculate using original rates.
| Tier | Employee Rate | Employer Rate | 2025 Wage Base |
|---|---|---|---|
| Tier 1 Retirement | 6.2% | 6.2% | $176,100 |
| Tier 1 Medicare | 1.45% | 1.45% | Unlimited |
| Tier 2 | 4.9% | 13.1% | $130,800 |
Additional Medicare (0.9%) on wages over $200,000 (single). Use Pub. 15 for sick pay adjustments.
IRS Form CT-1X Download and Printable
Download and Print: IRS Form CT-1X
Claiming Refunds or Adjustments on Form CT-1X
- Adjustment Process: Line 1 box—recoup overpayments against future liabilities; notify employees via W-2c if withholding affected.
- Refund Claims: For closed years; IRS issues check (6-8 weeks); no interest on refunds under $10.
- Certifications: Lines 4/5 protect withheld taxes; attach SSA correspondence if no W-2c needed.
Offsets: Credit against other IRS debts; elect direct deposit on line 26.
Common Mistakes When Filing Form CT-1X and How to Avoid Them
Pitfalls can trigger audits—avoid these:
- Wrong Year Rates: Using 2025 rates for 2024 corrections—stick to original.
- Incomplete Explanations: Vague Part III—detail errors with payroll docs.
- Missing W-2c Coordination: For employee impacts—file concurrently with SSA.
- Late Payments: Ignoring discovery deadlines—calendar equivalents to February 28.
- Form 945-A Oversights: Semiweekly filers must reconcile deposits.
Review with a payroll specialist; e-file Form CT-1 originally to ease adjustments.
Penalties for Late or Incorrect Form CT-1X Filings
Corrections mitigate but don’t erase:
- Late Filing/Payment: 5%/month (max 25%) + 0.5%/month interest.
- Failure to Deposit: 10% of underpayment for 15+ days late.
- Negligence: 20% of underpayment; fraud 75%.
- Relief: Reasonable cause waiver; first-time abatement via Form 843.
Document errors promptly—limitations start from original due date.
Frequently Asked Questions About IRS Form CT-1X
When should I file Form CT-1X for 2024 errors discovered in 2025?
By March 2, 2026; pay additional taxes timely to avoid interest.
Can I adjust Tier 2 taxes without refiling W-2s?
Yes, if no employee impact; certify on lines 4/5.
What’s the 2025 Tier 1 wage base?
$176,100, up from $168,600 in 2024.
Is e-filing available for CT-1X?
No—paper only; mail to Kansas City IRS Center.
How do I claim a refund over $10,000?
Via adjustment or direct claim; expect 6-8 weeks processing.
Visit IRS.gov/FormCT1X for more.
Final Thoughts: Correct RRTA Taxes Efficiently with Form CT-1X in 2025
IRS Form CT-1X safeguards railroad employers from error fallout, allowing seamless adjustments to RRTA liabilities amid 2025’s $176,100 Tier 1 cap and stable rates. With limitations expiring on older deferrals, act swiftly on discoveries to claim refunds or pay dues without excess interest. Download the April 2025 form from IRS.gov today and integrate with payroll software for accuracy.
Compliance funds retiree benefits—make it count.
This article is informational only—not tax advice. Consult IRS or a professional.








