Form 1125-A is eight lines long. It is also the place where the same number has to appear in three different spots on the return, and where a mismatch you introduce this year will still be causing problems in 2029.
It attaches to the 1065, the 1120 and the 1120S. Same form, same lines, whichever entity you are working on.
The eight lines
Line 1, inventory at beginning of year. This is the one that matters most and gets the least attention. More on it below.
Line 2, purchases. Goods bought for resale, or raw materials. Net of returns and allowances.
Line 3, cost of labor. Direct production labor only. Not the office manager, not the salespeople, not the owner unless the owner is on the floor making things. This line is not a place to park payroll you did not know where else to put.
Line 4, additional section 263A costs. The UNICAP line. Skip to the section below before you put a zero here reflexively.
Line 5, other costs. Freight in, factory overhead, production supplies. Freight *out* is a selling expense and does not belong here.
Line 6 is the sum. Line 7 is ending inventory. Line 8 is cost of goods sold, being line 6 minus line 7.
Simple arithmetic. The trouble is entirely in what feeds it.
Line 1 has to agree with two other things
Beginning inventory is not a number you decide. It is a number you inherit, and it has to match:
Last year's line 7. Ending inventory on the prior return is this year's beginning inventory. No exceptions, no rounding, no "close enough."
The beginning balance on Schedule L. The balance sheet carries inventory too, and the beginning column has to show the same figure.
Three places, one number. When they disagree, you have either a prior year error, an unrecorded inventory adjustment, or a client who did a physical count and adjusted the books without telling anyone. All three are worth knowing about, and all three are invisible if you type the beginning inventory straight off the client's current-year balance sheet without checking it against the prior return.
That last habit is the one to break. The client's book beginning inventory is what their accounting system says. The prior return is what you told the IRS. If those differ, the difference does not go away by picking the more convenient one.
Section 263A, and why the zero is sometimes wrong
UNICAP requires certain indirect costs to be capitalized into inventory rather than expensed. Line 4 is where those additional costs land.
There is a small business exception based on average annual gross receipts, and the threshold is indexed for inflation, so check the figure for the year you are filing rather than trusting a number you memorized. Most small clients fall under it comfortably and line 4 is genuinely zero.
But "most" is not "all," and a client who has been growing steadily can cross the threshold in a year when nothing else about the business felt different. If the client carries meaningful inventory and receipts have been climbing, it is worth five minutes to confirm which side of the line they are on rather than copying last year's zero forward.
The inventory method questions nobody reads
Below the arithmetic, the form asks how closing inventory was valued: cost, lower of cost or market, or another method. It asks whether there was a writedown of subnormal goods. It asks whether the LIFO election is in effect and, if so, wants Form 970 attached the year you make it.
It also asks whether there was any change in determining quantities, costs or valuations between opening and closing inventory. Answering that honestly means actually knowing what the client did, which means asking.
These are checkboxes, so they get clicked past. They are also representations on a filed return, and a LIFO election in particular is not something to discover retroactively.
Inventory is where book and tax quietly diverge
A few things to watch that produce M-1 differences or plain errors:
Obsolete inventory reserves. A book reserve for slow-moving goods is not deductible for tax until the goods are actually disposed of or written down under the specific rules. The reserve is a book to tax difference, not a COGS adjustment.
Shrinkage. Real, and deductible, but it needs to show up as an inventory adjustment rather than being buried in purchases where it distorts the gross margin comparison year over year.
Freight and handling. Freight in belongs in COGS. Freight out belongs in selling expenses. Clients mix these constantly because the invoices look identical.
Owner labor. If the owner draws a salary and also works in production, some of that compensation may belong in cost of labor rather than officer compensation. On an 1120S that split matters for a separate reason, since compensation of officers is reported on its own line.
Getting the three numbers to agree
Everything above is a reconciliation problem: beginning inventory has to tie to two other places, COGS has to tie to the books, and the whole thing has to land on the return consistently.
This is what Ledger IQ does before you open the tax software. You upload the trial balance and map each account to a real line on the return, with COGS accounts mapping to their Form 1125-A lines and the inventory asset mapping to its Schedule L line, so the same underlying balance drives both rather than being typed twice.
Schedule L beginning balances can be entered as an optional check. Enter last year's ending inventory and the workpaper tests it against what the current file says, which is exactly the beginning-inventory mismatch described above, caught in the first five minutes instead of the last five.
Adjusting entries for shrinkage or a physical count adjustment post against the trial balance with references, so the difference between what the client's books said and what you filed is documented rather than remembered. Book to tax items like an obsolescence reserve post separately as tax journal entries with their own M-1 offset, which keeps the client's financial statements intact while the difference stays visible.
Ledger IQ supports Forms 1065, 1120S and 1120, with exports for Drake, Lacerte and UltraTax CS. It is free during early access, so you can try it at portal.ledgeriq.ai on a live client without a credit card.