Updated September 29, 2026. Quick answer: Box 13 code A is a credit for estimated taxes the estate or trust allocated to you, treated as an estimated tax payment, and code B is backup withholding, entered on Form 1040 line 25c. Code B is the one case where the instructions say to attach the K-1 to your return.
The two payment-type codes
The instructions read here are the 2025 edition of the IRS Instructions for Schedule K-1 (Form 1041) for a Beneficiary Filing Form 1040 or 1040-SR (Catalog Number 11374Z, dated March 13, 2025), the edition served at the IRS standing PDF address when read on September 29, 2026. They are written for the beneficiary; the fiduciary’s own instructions are in the Instructions for Form 1041. The form’s page 2 lists both:
| Code | Form label | Report on (form’s code list) |
|---|---|---|
| A | Credit for estimated taxes | Form 1040 or 1040-SR, line 26 |
| B | Credit for backup withholding | Form 1040 or 1040-SR, line 25c |
Code A, credit for estimated taxes
“The beneficiary treats this amount as a payment of estimated tax.” “treat the amount entered in box 13, code A, as an estimated tax payment made on January 15, 2026.” That date matters for the underpayment penalty on Form 2210, and it is the date the instructions give for the 2025 edition. The credit depends on the fiduciary having filed the allocation form: “Form 1041-T, Allocation of Estimated Tax Payments to Beneficiaries, must be timely filed by the fiduciary for the beneficiary to get the credit for an estimated tax payment.”
Code B, credit for backup withholding
“Include this amount on line 25c of your Form 1040 or 1040-SR and attach a copy of Schedule K-1 (Form 1041) to your return.”
The one case where you file the K-1
Most K-1s stay with your records: “Don’t file it with your tax return, unless backup withholding was reported in box 13, code B.” The Reminders section repeats it: “If Schedule K-1 shows backup withholding in box 13, code B, attach a copy to your return.” The wider rules on filing and correcting a K-1 are on the Schedule K-1 for estates page.
Common mistakes
- Filing every K-1 with your return. The instructions say only a K-1 showing backup withholding in code B is attached.
- Treating a code A credit as paid on the K-1 date. The instruction dates it January 15, 2026 for the 2025 edition.
- Assuming a code A credit without the fiduciary’s Form 1041-T.
Related: Schedule K-1 (Form 1041) Box 12: Alternative Minimum Tax, Schedule K-1 (Form 1041) Box 13: Every Credit Code, and what a K-1 from an estate reports.
Every box and code in one place: the Schedule K-1 (Form 1041) boxes table. What a K-1 from an estate reports overall is on the Schedule K-1 for estates page.
Sources
- IRS, Instructions for Schedule K-1 (Form 1041) for a Beneficiary Filing Form 1040 or 1040-SR (2025): https://www.irs.gov/pub/irs-pdf/i1041sk1.pdf
- IRS, Schedule K-1 (Form 1041) 2025, Beneficiary’s Share of Income, Deductions, Credits, etc., page 2 code list: https://www.irs.gov/pub/irs-pdf/f1041sk1.pdf
Source: the IRS instructions for the beneficiary who receives Schedule K-1 (Form 1041), and the form’s own code list, read at irs.gov on September 29, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer, the estate’s or trust’s fiduciary or the IRS is the right place to confirm anything consequential.