Box 13, letter by letter
Schedule K-1 box 13 codes: which form each letter feeds, and how to prove it
Box 13 is the one box where a single letter decides what a number means. Read it as pairs — letter, then amount — and check each pair against the statement behind it. That is a job you can finish and demonstrate in a few minutes per K-1.
The letters are not decoration on top of the amount. They are the meaning. Two K-1s with the same figure in box 13 can send that figure to a charitable contribution schedule on one and to an investment interest carryforward on the other, and nothing on the page except the letter tells you which.
Code titles below are the 2025 list for Form 1065. They change between years. K1 FastTax exports code letters and amounts only, never a title, so the letter on your K-1 is always the thing to look up.
The list
Where the letters go, grouped by what they cost if you get it wrong
Sorted by the mistake rather than by the alphabet. A preparer who has read a hundred K-1s does not need the letters in order; they need to know which ones carry a limit, a second form, or a statement.
| Group | Letters | Destination | What the letter actually carries |
|---|---|---|---|
| Contributions | A, B, C, D, E, F, G | Schedule A, lines 11 and 12 | The letter carries the AGI limit, not just the destination. A 60% cash gift entered under B changes what the client can deduct this year. |
| Investment interest | H | Form 4952, line 1 | Often paired with box 5 interest income. If box 5 is blank and H is not, the client is paying investment interest without investment income, and the carryforward starts here. |
| Royalty and portfolio deductions | I, L, AE | Schedule E line 19; Schedule A line 16 | Small amounts that get dropped because they look like noise. Every one of them is a deduction the client loses. |
| Section 59(e)(2) and EBIE | J, K | Form 4562 election; Form 8990 | K is the one that grows a filing obligation. Excess business interest is not deductible this year and it is not gone either. |
| Medical insurance and benefits | M, N, O | Schedule 1 line 17; Schedule E line 28 (capped); Form 2441 Part III | M is a self-employed health insurance deduction that only works if the client had a profit in box 1. A box 1 loss makes it disappear. |
| Pensions, reforestation, film | R, S, X | Schedule 1 line 16; Schedule F; the production expense statement | R is where a partner's own retirement plan contribution comes from on a K-1 that carries it. |
| Conservation and barrier removal | W, Y | Schedule F line 12; deduction with an annual cap | W changed meaning in the recent past, which is the whole reason to read the letter against the year printed on the K-1. |
| Net section 743(b) adjustment | V | Partner-level basis computation, not a deduction line | A negative 743(b) adjustment is easy to mistake for a loss. It is a basis item and it belongs with the partner's own schedule. |
| Reserved letters | Q, T, U, AF to AJ | Nothing | A letter that is reserved in the current year is a snapshot of a form printed in a different year. Do not interpret it, look it up. |
| Itemized deductions and everything else | Z, ZZ, AA, AB, AC, AD | Schedule A line 16; the attached statement | Z almost never carries an amount. It says there is a statement, and the statement is the actual content. |
Full destination notes for this box are on the box 13 page of the box guide.
Five steps, in the order a return actually goes
- 1Copy the letter and the amount as one pair. Box 13 is not a column of numbers, it is a list of letter-and-amount pairs. If the worksheet records them as two separate things, the pairing is lost and nothing downstream can be checked.
- 2Mark STMT as STMT, never as zero. A letter with STMT in the amount space means the figure is on the attached statement. Writing zero turns an incomplete document into a wrong return, and nobody can see it afterwards.
- 3Read the year off the K-1 header. The letters are year-specific. A 2024 K-1 read against the 2025 list can put a real deduction in the wrong place, and the amount will look plausible.
- 4Match the statement line to the letter, not to the description. Statements describe items in the partnership's own words. The letter is the only stable key. Take the letter from the K-1 and find that letter on the statement.
- 5Add up the statement and compare. If the statement breaks one letter into several lines, the lines must sum to the amount printed in box 13 for that letter. If they do not, one of the two is not the same year or not the same partner.
The check that catches a misread box 13
One rule holds the whole box together: every letter on the K-1 has either an amount or the word STMT, and every statement line belongs to a letter that is on the K-1. Run it as three comparisons.
- Count the letters. The number of distinct letters in box 13 must equal the number of letters in the worksheet row. Two letters collapsed into one row is the most common way an amount gets attached to the wrong deduction.
- Count the STMTs. Every STMT must correspond to a page in the attachment. A STMT with no page behind it means the document you were given is not the whole document.
- Add the statement up. Where the statement splits one letter across lines, the lines must total the amount printed for that letter. When they do not, check the partner name in the statement header before you check anything else, because the arithmetic will agree with whichever investor the statement was built for.
When the third comparison fails and the header is right, the usual cause is an allocation: the statement reports the item at the partnership level and part of it stays with the entity. That is a question for the issuer, not something to solve by adjusting a number.
Three things that break, and what each one looks like
| What you see | What it usually is | Where to go |
|---|---|---|
| A letter with a blank amount | A STMT that was trimmed off, or a letter that carries only an asterisk | Back to the page. If there is no statement in the file, ask the issuer for one before the return is keyed. |
| Two letters from different years on the same form | A K-1 template reused without updating the code list | The year in the header decides. Read one list only, and note the conflict on the worksheet. |
| An amount in box 13 with no letter | A column shift in the source PDF, or a letter printed in a separate column that did not get read | Do not assign a letter to make the row tidy. Hold the row, print the page, and read it by eye. |
The discipline is the same one that applies to an attached statement of any kind: characters go across as printed, and anything doubtful is flagged rather than resolved. The statement attachment guide covers what to record when the box points off the page.
What this looks like in the CSV
The coded boxes come out as pairs separated by semicolons — A:1200;H:340;W:0 — with STMT kept as the word rather than replaced by a figure, and a code whose amount could not be read with confidence held for review instead of filled in. The column is text on purpose: a letter plus an amount is not a number and should never be summed as one.
Plain answers
Questions about box 13
What are the box 13 codes for Schedule K-1 (Form 1065) in 2025?
A through G are charitable contributions split by the AGI limit that applies; H is investment interest expense; I is deductions for royalty income; J is section 59(e)(2) expenditures; K is excess business interest expense; L is other portfolio deductions; M is medical insurance; N is educational assistance; O is dependent care; P is preproductive period expenses; R is pensions and IRAs; S is reforestation; V is a net section 743(b) basis adjustment; W is soil and water conservation; X is qualified production expenses; Y is removal of architectural barriers; Z is itemized deductions; AA through AD cover capital construction fund, early withdrawal penalties and debt-financed distribution interest; ZZ is other. Letters Q, T, U and parts of the AF to AJ range are reserved. Read the list in the instructions for the year printed on your K-1, because letters get added and reused.
Why does box 13 show a letter with no amount?
Because the amount is on an attached statement, marked STMT, or because the partnership put an asterisk beside the code to point at a statement that explains it. In neither case is the item zero. Record the letter, record that a statement exists, and put the page of the statement next to it so the person reviewing the return does not have to go looking.
Can the same letter mean something different in two years?
Yes, and that is the single most expensive thing about box 13. Letters are added, retired and re-titled as the form changes. A letter that reads correctly against last year's list may point at a different deduction this year, and the amount will still look ordinary. Always read the letter against the instructions for the tax year in the K-1 header, not against the list you memorised.
How do I check a box 13 amount against the attached statement?
Take the letter from the K-1, find that letter on the statement, and add every line that belongs to it. The total has to equal the amount printed beside the letter in box 13. If the statement gives more than the K-1 does, the missing part is usually a line that was allocated to the partnership rather than to this partner. If it gives less, one line was dropped.
Does K1 FastTax read the box 13 statement?
No, on any plan. It reads the letters and amounts printed on the K-1, marks a letter that says STMT as STMT rather than guessing a number, and records the page each value came from. The statement itself is yours to read and to reconcile against those letters, and this guide is the method for doing it.
Letters and amounts, kept as pairs
K1 FastTax reads the box 13 letters and amounts from a K-1 PDF, keeps STMT as STMT, and records the page each one came from so the statement behind it can be found again.