Inventory Valuation Methods: IRS Rules, LIFO Conformity, and Penalties

Inventory valuation methods are the accounting approaches a business uses to assign a dollar cost to unsold goods at the end of a period, and U.S. tax law recognizes four: first-in, first-out (FIFO); last-in, first-out (LIFO); weighted average cost; and specific identification. The method you pick controls both your cost of goods sold and your taxable income, and once you adopt one, the IRS expects you to stay with it unless you formally request a change.

The Four Cost Flow Methods

Every business holding inventory has to decide which cost layers attach to the goods that leave and which stay on the books. The four methods produce different ending inventory values and different cost of goods sold, even when the physical goods on the shelf are identical.

First-In, First-Out

FIFO assumes the oldest costs are matched to sales first. What remains on the books reflects the prices you paid most recently. When prices are rising, FIFO produces a higher ending inventory value and a lower cost of goods sold, which means higher reported profit. It often mirrors the physical reality of perishable goods moving off shelves in the order they arrived.

Last-In, First-Out

LIFO flips the assumption. The most recent costs get matched against revenue first, leaving the oldest and often cheapest cost layers sitting in ending inventory. During inflationary periods, this pushes up cost of goods sold and reduces taxable income. Tax deferral is the main reason businesses elect LIFO, but the election comes with a conformity requirement covered further down.

Weighted Average Cost

The weighted average method blends all purchase costs together by dividing the total cost of goods available for sale by the total number of units. Every unit on hand carries the same per-unit cost. This smooths out price swings and simplifies record-keeping, especially for businesses that commingle inventory from multiple purchase lots. Under a perpetual system, the average recalculates with every new shipment.

Specific Identification

Specific identification tracks every individual unit by serial number, lot number, or RFID tag, linking each sale to the exact cost paid for that item. It is the most precise method but only practical for high-value, low-volume goods like vehicles, fine jewelry, or custom equipment. For commodity-type products where units are interchangeable, the record-keeping burden makes it impractical.

What Counts as Inventory Cost

Inventory cost is not just what appeared on the invoice. For tax purposes, the cost of inventory must reflect all expenses necessary to bring goods to their present condition and location: the purchase price, inbound freight, import duties and tariffs, and handling charges incurred before the goods reach your selling floor or warehouse.¹

Manufacturers face a broader set of includable costs. Direct materials and direct labor are obvious, but the IRS also requires certain indirect costs to be folded into inventory under the Uniform Capitalization (UNICAP) rules of IRC Section 263A. Those indirect costs include storage, insurance, utilities at production facilities, quality control, and purchasing department overhead.² The practical effect is that many overhead items you might instinctively treat as current-year expenses have to be capitalized into inventory and deducted only when the goods sell.

Section 263A applies to any business that produces property or acquires it for resale, unless a small business exemption applies. The exemption is available to taxpayers whose average annual gross receipts over the prior three years do not exceed $32 million for tax years beginning in 2026.³⁴ If your business clears that threshold, you must capitalize the full range of direct and indirect production costs. Allocation errors here are one of the most common audit adjustments for mid-size manufacturers and distributors.

Writing Inventory Down Below Cost

Accounting rules do not let you carry inventory at a value higher than what you could actually recover by selling it. The specific test depends on the cost flow method.

For businesses using FIFO or weighted average cost, the current standard requires measuring inventory at the lower of cost and net realizable value. Net realizable value is the estimated selling price minus the costs to complete, sell, and deliver the goods. If that figure drops below what you originally recorded, you write the inventory down.⁵ This replaced the older lower of cost or market test.

Businesses using LIFO or the retail inventory method still apply the older lower of cost or market framework. Under that test, “market” means current replacement cost, capped at net realizable value and floored at net realizable value minus a normal profit margin.⁵

Physical damage, obsolescence, and loss of consumer demand are the most common triggers. The review should happen at each reporting period. Once you write inventory down, the reduced amount becomes the new cost basis.

How the Method Affects Profit and Taxes

The number you assign to ending inventory moves through two statements at once. On the income statement, cost of goods sold equals the cost of goods available for sale minus ending inventory. A higher ending inventory value produces a lower cost of goods sold and a higher gross profit. On the balance sheet, that same ending inventory sits as a current asset.

A company using FIFO during a period of rising prices will report both higher profits and higher asset values than an identical company using LIFO. Neither number is wrong, but they tell different stories to lenders, investors, and the IRS.

IRS Consistency and Changing Your Method

IRC Section 471 requires any business for which inventories are necessary to clearly determine income to account for those inventories on a basis that conforms to best practices in its industry and most clearly reflects income.⁶ Once you adopt a method, the IRS expects you to stick with it. Year-to-year shopping between methods to minimize tax is exactly what the code is designed to prevent.

To change methods, file Form 3115 (Application for Change in Accounting Method). Many inventory-related changes qualify for the automatic consent procedure, which grants IRS approval as long as you meet the eligibility requirements and file the form with your return. No user fee applies for automatic changes.⁷ Changes outside the automatic list require a formal request to the IRS National Office, with a user fee and a longer review.

The part that catches business owners off guard is the Section 481(a) adjustment. When you switch methods, you calculate the cumulative difference between your old method and your new one as of the beginning of the year of change. That prevents income from being duplicated or skipped. A positive adjustment (one that increases income) generally spreads ratably over four tax years. A negative adjustment takes full effect in the year of change.⁸ For positive adjustments under $50,000, you can elect to recognize the whole amount in a single year.

Small Business Exemptions

If your average annual gross receipts over the prior three tax years do not exceed $32 million (the inflation-adjusted threshold for 2026), you may qualify for two separate exemptions that simplify inventory accounting considerably.⁴

Section 471(c) lets qualifying small businesses skip formal inventory accounting altogether. You can treat inventory as non-incidental materials and supplies, deducting the cost in the year you use or sell the goods rather than maintaining cost layers. Or you can follow whatever inventory method appears in your audited financial statements, or if you do not have audited statements, your internal books.⁶

Section 263A’s UNICAP rules also do not apply to businesses meeting the same gross receipts test. You are not required to capitalize indirect production costs like warehouse utilities, insurance, or storage into inventory value.³ Switching to one of these simplified methods still requires Form 3115 and a Section 481(a) computation, but the statute treats the change as made with IRS consent.⁶

The LIFO Conformity Rule

Businesses that elect LIFO for tax purposes face a requirement that does not apply to any other inventory method. Under IRC Section 472, you must also use LIFO in all financial reports issued to shareholders, partners, creditors, or other outside parties.⁹ You cannot report higher FIFO-based profits to your bank while claiming lower LIFO-based income on your tax return.

The conformity requirement is strictly enforced. If the IRS finds that your primary financial statements use a different method, it can disqualify the LIFO election entirely. Losing the election means restating potentially years of inventory at FIFO or another method, which can create a large, immediate tax liability from the recaptured LIFO reserve. Companies using LIFO should audit their external financial reporting, including supplemental reports sent to lenders, to be sure no version uses a non-LIFO figure as the primary presentation.

Penalties for Getting It Wrong

Inventory errors that result in underpaid taxes carry escalating consequences depending on severity and intent.

For negligence or careless disregard of IRS rules, Section 6662 imposes an accuracy-related penalty equal to 20% of the resulting tax underpayment. A gross valuation misstatement doubles the penalty to 40%.¹⁰ The 40% tier applies when the value or adjusted basis of property claimed on a return is 200% or more of the correct amount.

Deliberate manipulation of inventory values to understate income crosses into criminal territory. Tax evasion under IRC Section 7201 is a felony carrying up to five years in federal prison.¹¹ Section 7201 sets the individual fine at $100,000 ($500,000 for corporations), and the general federal sentencing statute raises the effective maximum for individuals to $250,000 for any felony conviction where the offense statute has not opted out. Section 7201 has not opted out.¹² Inflating ending inventory to reduce cost of goods sold, fabricating purchase records, or omitting inventory from returns are the kinds of conduct that draw criminal referrals. The line between a careless mistake and willful evasion often comes down to documentation, and businesses with sloppy records have a much harder time proving they acted in good faith.

1
eCFR. 26 CFR 1.471-4 – Inventories at Cost or Market, Whichever Is Lower
2
Internal Revenue Service. Section 263A Costs for Self-Constructed Assets
3
Office of the Law Revision Counsel. 26 USC 263A – Capitalization and Inclusion in Inventory Costs of Certain Expenses
4
Internal Revenue Service. Rev. Proc. 2025-32
5
Financial Accounting Standards Board (FASB). Accounting Standards Update No. 2015-11 – Inventory (Topic 330): Simplifying the Measurement of Inventory
6
Office of the Law Revision Counsel. 26 USC 471 – General Rule for Inventories
7
Internal Revenue Service. Instructions for Form 3115
8
Internal Revenue Service. IRM 4.11.6 Changes in Accounting Methods
9
Office of the Law Revision Counsel. 26 USC 472 – Last-In, First-Out Inventories
10
Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments
11
Office of the Law Revision Counsel. 26 USC 7201 – Attempt to Evade or Defeat Tax
12
Office of the Law Revision Counsel. 18 USC 3571 – Sentence of Fine