GAAP Inventory Methods

Under U.S. GAAP (ASC 330), companies may use several inventory costing methods: First-In, First-Out (FIFO), Last-In, First-Out (LIFO), weighted-average cost, and specific identification. FIFO assumes the oldest inventory is sold first, resulting in a balance sheet that reflects the most recent costs. LIFO assumes the most recently purchased inventory is sold first, which during inflationary periods reduces taxable income but leaves older, lower-cost inventory on the balance sheet. Weighted-average cost blends all purchase costs equally across units available for sale. Specific identification is used for high-value, distinguishable items such as vehicles or jewelry. Companies must consistently apply the chosen method and disclose it in their financial statements. A critical GAAP vs. IFRS distinction: LIFO is permitted under U.S. GAAP but prohibited under IFRS, making inventory method selection an important consideration for companies with international operations or reporting obligations.

The lower of cost or net realizable value (LCNRV) rule under ASC 330 requires companies to write down inventory when its carrying value exceeds the amount expected to be realized through sale in the ordinary course of business. Net realizable value (NRV) is defined as estimated selling price less reasonably predictable costs of completion and disposal. If inventory's NRV falls below its recorded cost—due to obsolescence, damage, price declines, or changes in demand—a write-down to NRV is required. Once written down, inventory cannot be written back up under GAAP, unlike IFRS which allows reversals. The LCNRV write-down is recognized as a loss in the period it occurs. This principle ensures that inventory is not overstated on the balance sheet, upholding the conservatism principle fundamental to GAAP-based financial reporting and protecting stakeholders from misleading balance sheet values.

The inventory costing method chosen significantly affects reported profitability, tax liability, and balance sheet strength. During periods of rising prices, FIFO produces lower cost of goods sold (COGS), higher net income, and a higher inventory balance reflecting current market values. LIFO produces higher COGS, lower taxable income, and a lower (often outdated) inventory balance. Weighted average falls between these extremes. These differences ripple through key financial ratios: gross margin, current ratio, inventory turnover, and return on assets all shift depending on the method used. Analysts comparing companies using different inventory methods must make adjustments—particularly when comparing LIFO companies to FIFO or international peers. The LIFO reserve disclosure required under GAAP allows users to convert a LIFO company's results to a FIFO basis for meaningful comparability across reporting entities.

ASC 330 requires companies to disclose sufficient information for users to understand the composition and valuation of inventory balances. Required disclosures typically include: the accounting policies used (FIFO, LIFO, weighted average, or specific identification), the major components of inventory (raw materials, work-in-process, and finished goods for manufacturers), and any significant write-downs to NRV recognized during the period along with the circumstances that led to them. Companies using LIFO must also disclose their LIFO reserve—the cumulative difference between LIFO and FIFO inventory values—enabling financial statement users to assess the impact of the LIFO method on reported results. For companies with significant inventory balances, these disclosures are among the most scrutinized notes by analysts and auditors, as they reveal management's judgment in estimating obsolescence, market values, and expected selling prices.

Under GAAP, inventory must be written down when its carrying cost exceeds net realizable value, and written off entirely when the inventory has no remaining recoverable value—due to spoilage, obsolescence, theft, or physical damage. A write-down reduces inventory to NRV and records a corresponding loss in cost of goods sold or a separate line item if material. A full write-off removes the inventory from the balance sheet entirely. Both require supporting documentation of the NRV assessment and any physical counts confirming inventory condition. Under ASC 330, once inventory is written down, that lower value becomes the new cost basis—subsequent recovery of value is not recognized under GAAP. Companies with seasonal products, technology goods, perishables, or fashion merchandise face elevated write-down risk and should establish robust processes for identifying and documenting impaired inventory on a timely basis.