Overview of the Process

To correct a previously filed Form CT-1, use Form CT-1 X to file either an adjusted railroad retirement tax return or a claim for refund or abatement. The adjustment process and the claim process are outlined below.

If you underreported the tax. If you underreported the tax on a previously filed Form CT-1, check the box on line 1 and pay any additional amount you owe by the time you file Form CT-1 X. For details on how to make a payment, see the instructions for line 26, later.

How Should You Make Entries on Form CT-1 X? You can help the IRS process Form CT-1 X timely and accurately if you follow these guidelines.

• Type or print your entries.

• Use Courier font (if possible) for all typed or computer-generated entries.

• Omit dollar signs. You may use commas and decimal points, if desired. Enter dollar amounts to the left of any preprinted decimal point and cents to the right of it.

• Always show an amount for cents, even if it is zero. Don’t round entries to whole dollars.

• Complete all five pages and sign Form CT-1 X on page 5.

• Staple multiple sheets in the upper-left corner.

What About Penalties and Interest? Generally, your correction of an underreported tax amount won’t be subject to an FTP penalty, an FTD penalty, or interest if you:

• File on time (by the due date of the year in which you discover the error),

• Pay the amount shown on line 26 by the time you file Form CT-1 X,

• Enter the date you discovered the error, and

• Explain in detail the grounds and facts relied on to support the correction.

No correction will be eligible for interest-free treatment if any of the following apply.

• The underreported amounts relate to an issue that was raised in an examination of a prior period.

• You knowingly underreported your employment tax liability.

• You received a notice and demand for payment.

• You received a notice of determination under section

Instructions for Form CT-1 X (Rev. 4-2025) 5

Example—You underreported RRTA taxes. On June 20, 2025, you discovered an error that results in additional tax on your 2024 Form CT-1. File Form CT-1 X by March 2, 2026 (February 28, 2026, is a Saturday), and pay the amount you owe by the time you file. See When Should You File Form CT-1 X, earlier. Don’t attach Form CT-1 X to your 2025 Form CT-1.

If you overreported the tax. If you overreported the tax on a previously filed Form CT-1, choose one of the following options.

• Use the adjustment process. Check the box on line 1 to apply any credit (negative amount) from line 26 to Form CT-1 for the year during which you file Form CT-1 X.

• Use the claim process. Check the box on line 2 to file a claim on Form CT-1 X requesting a refund or abatement of the amount shown on line 26.

To ensure that the IRS has enough time to

TIP process a credit for an overreporting tax

adjustment in the year during which you file Form CT-1 X, you’re encouraged to file Form CT-1 X correcting the overreported tax amount in the first 11 months of a year. For example, if you discover an overreported tax amount in December, you may want to file Form CT-1 X in the first 11 months of the next year. However, there must be 90 days remaining on the period of limitations when you file Form CT-1 X. See the Caution under Is There a Deadline for Filing Form CT-1 X , earlier. This should ensure that the IRS will have enough time to process the Form CT-1 X so that the credit will be posted before you file Form CT-1, thus avoiding an erroneous balance due notice from the IRS. See the example next.

Example—You want your overreported tax applied as a credit on Form CT-1. On December 19, 2025, you discover you overreported your tax on your 2024 Form CT-1 and want to choose the adjustment process. To allow the IRS enough time to process the credit, you file Form CT-1 X on March 10, 2026, and take the credit on your 2026 Form CT-1.

To ensure that the IRS has enough time to

TIP process a credit for an overreporting tax

adjustment in the year during which you file Form CT-1 X, you’re encouraged to file Form CT-1 X correcting the overreported tax amount in the first 11 months of a year. For example, if you discover an overreported tax amount in December, you may want to file Form CT-1 X in the first 11 months of the next year. However, there must be 90 days remaining on the period of limitations when you file Form CT-1 X. See the Caution under Is There a Deadline for Filing Form CT-1 X , earlier. This should ensure that the IRS will have enough time to process the Form CT-1 X so that the credit will be posted before you file Form CT-1, thus avoiding an erroneous balance due notice from the IRS. See the example next.