When Should You File Form 943-X?

File Form 943-X when you discover an error on a previously filed Form 943.

However, if your only errors on Form 943 relate to the number of employees (Form 943, line 1) or to federal tax liabilities reported on your Monthly Summary of Federal Tax Liability on Form 943, line 17, or on Form 943-A, Agricultural Employer’s Record of Federal Tax Liability, don’t file Form 943-X. For more information about correcting federal tax liabilities reported on your Monthly Summary of Federal Tax Liability on Form 943, line 17, or on Form 943-A, see the Form 943-A instructions.

Due dates. The due date for filing Form 943-X depends on when you discover an error and if you underreported or overreported tax. If you underreported tax, see Underreported tax, later. For overreported tax amounts, you may choose to either make an interest-free adjustment or file a claim for refund or abatement. If you’re correcting overreported tax amounts, see Overreported tax—Adjustment process and Overreported tax—Claim process , later.

If any due date falls on a Saturday, Sunday, or legal holiday, you may file Form 943-X on the next business day. If we receive Form 943-X after the due date, we will treat Form 943-X as filed on time if the envelope containing Form 943-X is properly addressed, contains sufficient postage, and is postmarked by the U.S. Postal Service (USPS) on or before the due date, or sent by an IRS-designated private delivery service (PDS) on or before the due date. If you don’t follow these guidelines, we will consider Form 943-X filed when it is actually received. See Pub. 15 for more information on legal

For help filing Form 943-X or for questions about federal employment taxes and tax corrections, you can:

• Go to IRS.gov/EmploymentTaxes and IRS.gov/ CorrectingEmploymentTaxes ;

• See Pub. 15; or

• Call the IRS Business and Specialty Tax Line toll free at 800-829-4933 or 800-829-4059 (TDD/TTY for persons who are deaf, hard of hearing, or have a speech disability), Monday–Friday from 7:00 a.m. to 7:00 p.m. local time (Alaska and Hawaii follow Pacific time; employers in Puerto Rico receive service from 8:00 a.m. to 8:00 p.m. local time).

Instructions for Form 943-X (Rev. 2-2026) 5

holidays. For more information about PDSs, see Where Should You File Form 943-X , later.

Underreported tax. If you’re correcting underreported tax, you must file Form 943-X by the due date of the return for the return period in which you discovered the error (January 31 of the following year) and pay the amount you owe by the time you file . Doing so will generally ensure that your correction is interest free and not subject to failure-to-pay (FTP) or failure-to-deposit (FTD) penalties. See What About Penalties and Interest, later. For details on how to make a payment, see the instructions for line 25, later.

If Form 943-X is filed late (after the due date of the return for the return period in which you discovered the error), you must attach an amended Form 943-A to Form 943-X. Otherwise, the IRS may assess an “averaged” FTD penalty. See “Averaged” FTD penalty in section 11 of Pub. 15 for more information about “averaged” FTD penalties. The total tax reported on Form 943-A, line M, must match the corrected tax (Form 943, line 13, combined with any correction reported on Form 943-X, line 20) for the year, less any previous abatements and interest-free tax assessments.

Example—You owe tax. On February 13, 2026, you discovered that you underreported $1,000 of social security and Medicare wages on your 2025 Form 943. File Form 943-X and pay the amount you owe by February 1, 2027 (January 31, 2027, is a Sunday), because you discovered the error in 2026 and February 1, 2027, is the due date for that year. If you file Form 943-X before February 1, 2027, pay the amount you owe by the time you file.

Caution: Form 943-X can’t be used to correct underreported amounts of Additional Medicare Tax unless the amounts were withheld from employee wages.

Overreported tax—Adjustment process. If you overreported tax and choose to apply the credit to Form 943, file an adjusted return on Form 943-X soon after you discover the error but more than 90 days before the period of limitations on the credit or refund for Form 943 expires. See Is There a Deadline for Filing Form 943-X, later.

Caution: Form 943-X can’t be used to correct overreported amounts of Additional Medicare Tax unless the amounts weren’t withheld from employee wages.

Example—You want your credit applied to Form 943. You filed your 2025 Form 943 on February 2, 2026, and payments were timely made. On May 4, 2026, you discover that you overreported tax on your 2025 Form 943. You file Form 943-X on June 5, 2026, and check the box on line 1 to indicate you want to use the adjustment process. The IRS treats your credit as a tax deposit made on January 1, 2026. When you file your 2026 Form 943, include the amount from Form 943-X, line 25, on the “Total deposits” line of your 2026 Form 943.

Overreported tax—Claim process. If you overreported tax on Form 943, you may choose to file a claim for refund or abatement on Form 943-X any time before the period of limitations on the credit or refund expires. If you also need to correct any underreported tax amounts, you must file

another Form 943-X reporting only corrections to the underreported tax amounts. See Is There a Deadline for Filing Form 943-X, later.

Caution: You may not file a refund claim to correct federal income tax or Additional Medicare Tax actually withheld from employees.