Taking inventory of stock for tax purposes means physically counting everything your business holds at the close of the period, assigning each item a value under an IRS-accepted method, reconciling those figures against your books, and documenting the adjustments well enough to defend them if the return is examined. Federal tax law requires inventories whenever the production, purchase, or sale of merchandise is a factor in how you earn income,1IRS. Publication 538 – Accounting Periods and Methods and errors that understate taxable income can trigger accuracy penalties of 20% or more. The process has four parts, and each one matters for a different reason.
Who Has to Take an Inventory
The general rule under Section 471 is that if merchandise is a factor in your income, you must maintain inventories, and the IRS has broad discretion to prescribe how those inventories are taken. Whatever method you use must conform to sound accounting practice and clearly reflect your income.2Office of the Law Revision Counsel. 26 U.S. Code 471 – General Rule for Inventories Using inventories generally locks you into accrual accounting for purchases and sales rather than the cash method.
There is a meaningful exception for smaller businesses. If your average annual gross receipts over the prior three tax years fall under the Section 448(c) threshold, you can treat inventory the same way you treat non-incidental materials and supplies, which is far simpler. That threshold is $31 million for tax years beginning in 2025, rising to roughly $32 million for 2026 with inflation adjustments.3IRS. Revenue Procedure 2024-40 Businesses above the ceiling do not get to skip the full inventory process.
Preparing for the Count
A defensible count starts with a clean setup. Generate count sheets or scanner records from your existing system so the team is verifying against a baseline rather than starting from zero. Each sheet needs columns for SKU, description, and storage location. Before anyone begins, tidy the shelves and tag anything that should be excluded, such as customer-owned goods on your floor or product already invoiced for outbound shipment. Those items are not yours to count.
Split the team into two roles. Counters physically verify what is on the shelf. Checkers independently validate the recordings. Keeping those duties separate catches honest mistakes and makes fraud harder. A supervisor floating between zones can resolve unit-of-measure questions in real time rather than after the fact.
Choosing a Counting System
Two frameworks dominate, and GAAP requires you to apply whichever you pick consistently from period to period.
Periodic
You count everything at set intervals, typically at the close of a quarter or fiscal year, and usually halt receiving and shipping while the team works. This fits smaller operations that do not need real-time stock data. The tradeoff is that theft, damage, or receiving errors between counts stay invisible until the next full count.
Perpetual With Cycle Counting
A perpetual system updates stock levels continuously as sales, purchases, and returns post through integrated software. You still need physical verification, but you do it in rotating pieces through cycle counting rather than shutting down the warehouse.
Most businesses prioritize cycle counts using ABC classification. “A” items, the highest-value or fastest-moving SKUs, are counted most often, sometimes weekly or monthly. “B” items are counted quarterly. “C” items, which make up the bulk of SKU count but a small share of total value, might be counted only once or twice a year. The point is to concentrate effort where an error costs the most money.
Choosing a Valuation Method
The count tells you how many units you have. The valuation method tells you what they are worth on the books, and that flows straight into cost of goods sold and taxable income. The IRS allows several methods.1IRS. Publication 538 – Accounting Periods and Methods
FIFO, LIFO, and Weighted Average
Under FIFO (first-in, first-out), the oldest items are treated as sold first, so ending inventory reflects newer, higher-cost purchases when prices are rising. That produces a lower cost of goods sold and higher taxable income. Under LIFO (last-in, first-out), the newest items are treated as sold first, producing a higher cost of goods sold, lower reported profit, and lower taxes during inflation. Weighted average splits the difference by averaging cost across all units available during the period.
A short illustration. You bought three units at $30, $31, and $32, then sold one for $40. Under FIFO, cost of goods sold is $30 and taxable gain is $10. Under LIFO, cost is $32 and gain is $8. Under weighted average, cost is $31 and gain is $9. Those spreads compound across thousands of transactions in a full year.
The LIFO Conformity Rule
LIFO has a condition attached. If you elect LIFO for federal tax, you must also use it in reports issued to shareholders and creditors.4Office of the Law Revision Counsel. 26 U.S. Code 472 – Last-in, First-out Inventories You cannot show higher earnings to a lender on FIFO while telling the IRS your profits were lower on LIFO. The election is made by filing Form 970 with the return for the first year you want to use the method, and once elected LIFO must be used in all subsequent years unless the IRS approves a change.
Changing Methods Later
Switching valuation methods after you have started is not a matter of doing the math differently next year. You file Form 3115, Application for Change in Accounting Method, and the change usually requires a Section 481(a) adjustment so income is not duplicated or skipped in the transition. Most businesses work with a tax professional before making the switch, because errors here take years to unwind.
Doing the Physical Count
The mechanics are simple, and the discipline matters. Move systematically through each storage area in a consistent pattern, usually top-to-bottom and left-to-right within an aisle. Record each item into a scanner or onto the count sheet as you go. Letting counters choose their own path is how items get missed or counted twice. Mark each completed section with a colored sticker or tag, especially when multiple teams work adjacent zones or stock lives in more than one building.
Watch units of measure closely. Counting individual pieces when the system tracks cases of twelve produces a discrepancy that looks catastrophic but is really a conversion error. Flag damaged or obsolete goods separately rather than mixing them in with sellable stock. Those items may need to be written down to a lower value during reconciliation, and you want them identified before that step, not after.
The recorded numbers become your ending inventory for the period, which drives cost of goods sold and, ultimately, reported profit. A count that is off by even a small percentage can meaningfully distort the financial statements you rely on for the return.
Reconciling and Adjusting the Books
Compare the physical count against what the accounting system says you should have. The difference is shrinkage, and it usually comes from some mix of theft, damage, and administrative errors like missed receiving entries or miscounted shipments. If the physical count comes in higher than book, you have an overage, which typically points to receiving that never got recorded.
Investigate any discrepancy worth investigating. Shrinkage concentrated in one product category or one section of the warehouse tells a different story than small variances scattered across the operation. The point is not just to adjust numbers but to find the cause so the same gap does not open next period.
How Shrinkage Is Treated on the Return
Shrinkage reduces ending inventory, which raises cost of goods sold and lowers taxable income. The IRS expects that reduction to be documented, not estimated loosely. Book inventories must be verified by physical counts at reasonable intervals and adjusted to conform with the physical results.5IRS. Revenue Procedure 98-29 Some businesses using the retail inventory method can estimate shrinkage between counts through a historical ratio based on actual shrinkage from the prior three tax years, but that safe harbor must be applied consistently across all stores in a trade or business. Changing how you estimate shrinkage requires Form 3115 and a detailed description of the new method.
What Getting It Wrong Costs
Inventory errors that understate taxable income by a substantial amount expose you to an accuracy-related penalty of 20% on the underpaid tax. A “substantial understatement” is one that exceeds the greater of 10% of the tax that should have been shown on the return, or $5,000.6Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments The rate rises to 40% in cases involving gross valuation misstatements.
If the IRS determines the understatement was fraud rather than carelessness, a separate penalty applies: 75% of the portion of the underpayment attributable to the fraud.7Office of the Law Revision Counsel. 26 U.S. Code 6663 – Imposition of Fraud Penalty Sloppy counting and deliberately inflated inventory are treated very differently. A documented counting process with independent verification and a clear audit trail is the practical defense against either finding, because it shows a good-faith effort to get the numbers right.