ASC 330 Inventory and LIFO Under US GAAP: Costing, Write-Downs and the IFRS Difference

Inventory accounting is where one of the sharpest US GAAP versus IFRS differences lives: LIFO. ASC 330 permits the last-in, first-out costing method that IFRS bans outright, and it handles inventory write-downs differently too. For manufacturers, retailers, and distributors, these rules shape cost of goods sold and reported margins. This guide explains inventory costing, the LIFO method, write-downs, and the framework differences.

How is inventory measured under ASC 330?

Inventory is initially recorded at cost, which includes all expenditures incurred to bring the inventory to its existing condition and location — purchase price, conversion costs such as direct labour and allocated production overhead, and other directly attributable costs. The cost is then assigned to units using a cost-flow method, and the inventory is subsequently measured at the lower of cost and net realisable value, or for LIFO and the retail inventory method, the lower of cost or market.

The lower-of-cost-and-net-realisable-value rule ensures inventory is not carried at more than it can be sold for, net of completion and selling costs. The measurement of inventory directly affects both the balance sheet and cost of goods sold, making it central to reported gross margin. For inventory-heavy businesses, the choice of cost-flow method and the discipline of write-downs are among the most significant accounting decisions, with direct consequences for profitability and tax.

What is LIFO and why is it allowed under US GAAP?

The last-in, first-out method assumes that the most recently acquired inventory is sold first, so cost of goods sold reflects the most recent costs and ending inventory reflects older costs. In a rising-price environment, LIFO produces higher cost of goods sold and lower reported profit — and, crucially, lower taxable income. This tax advantage is the main reason many U.S. companies use LIFO, and U.S. tax rules include a conformity requirement that links the tax and financial reporting use of LIFO.

LIFO is permitted under US GAAP but prohibited under IFRS, making it one of the clearest differences between the frameworks. The prohibition under IFRS reflects the view that LIFO does not faithfully represent the physical flow of inventory and can produce outdated balance-sheet values. Under US GAAP, however, LIFO remains a valid and widely used method, particularly in industries with rising input costs, and its tax benefits make it commercially attractive despite producing lower reported profit.

How do FIFO and weighted average compare?

US GAAP also permits first-in, first-out and weighted-average cost, both of which are allowed under IFRS as well. FIFO assumes the oldest inventory is sold first, so cost of goods sold reflects older costs and ending inventory reflects recent costs — the opposite of LIFO. In rising prices, FIFO produces lower cost of goods sold and higher reported profit than LIFO. Weighted-average cost blends all costs, smoothing the effect of price changes.

The choice among methods is significant and, once made, must be applied consistently. Because FIFO and weighted average are permitted under both frameworks, while LIFO is unique to US GAAP, a U.S. company using LIFO is not directly comparable to an IFRS reporter, and analysts often need to restate to a common basis. Companies using LIFO disclose the LIFO reserve — the difference between LIFO and what inventory would be under FIFO — which allows users to make this adjustment.

How are inventory write-downs handled?

When the utility of inventory falls below its cost — because of damage, obsolescence, declining prices, or other factors — ASC 330 requires it to be written down to its lower of cost and net realisable value (or lower of cost or market for LIFO and retail methods). The write-down is recognised as a loss in the period it occurs, typically within cost of goods sold, and it establishes a new cost basis for the inventory.

A key US GAAP feature is that, having written inventory down, the new lower basis generally cannot be reversed even if value subsequently recovers. This contrasts with IFRS, which permits reversing a previous write-down up to the original cost when net realisable value increases. The no-reversal rule makes US GAAP inventory accounting more conservative on recovery, and it means that a recovery in inventory value benefits future margins rather than reversing the earlier loss, a difference that matters for businesses with volatile inventory values.

Why do inventory differences matter for comparison?

The inventory differences between US GAAP and IFRS, especially LIFO, can make two otherwise identical companies look materially different. A U.S. company using LIFO will report higher cost of goods sold, lower gross margin, lower reported profit, and lower inventory values than an IFRS peer using FIFO, even with identical operations and prices. The no-reversal rule on write-downs adds a further, smaller difference. Naive comparison of margins or inventory turnover across the frameworks can therefore be badly misleading.

Analysts address this by using the LIFO reserve disclosure to restate a LIFO company to a FIFO basis before comparing it with IFRS reporters or with U.S. peers using FIFO. Understanding which method a company uses, and adjusting for it, is essential for meaningful cross-company and cross-framework analysis. This makes inventory one of the first things to check when comparing companies, particularly in manufacturing, retail, and distribution where inventory is a major asset, a point developed in our IFRS hub from the IFRS perspective.

What are LIFO layers and LIFO liquidations?

Under LIFO, inventory is conceptually organised into layers, each representing a year’s purchases at that year’s costs. In a stable or growing business with rising prices, older, lower-cost layers remain in ending inventory while current-period costs flow through cost of goods sold. A LIFO liquidation occurs when inventory quantities decline and these old, low-cost layers are charged to cost of goods sold, which can artificially boost reported profit because cost of goods sold reflects outdated low costs rather than current higher costs.

LIFO liquidations can therefore distort earnings, making a period look more profitable than the underlying operations justify, and they must be disclosed so users can understand the effect. They often arise when a company reduces inventory levels, for instance during a downturn or a strategic inventory reduction. Understanding LIFO layers and the liquidation effect is important for analysing a LIFO company’s results, because a profit increase driven by liquidating old layers is not a sustainable operational improvement, a nuance that has no equivalent under IFRS, which prohibits LIFO entirely.

How do you account for inventory costs and overhead?

Inventory cost under ASC 330 includes not only the purchase or production cost of the goods themselves but also conversion costs — direct labour and a systematic allocation of fixed and variable production overhead. The allocation of fixed overhead is based on the normal capacity of the production facilities, and abnormal amounts of idle facility expense, freight, handling, and spoilage are expensed in the period incurred rather than capitalised into inventory. This prevents inventory from absorbing the cost of underused capacity.

Getting overhead allocation right is significant for manufacturers, because it affects both the value of inventory on the balance sheet and the cost of goods sold when inventory is sold. Over-absorbing overhead into inventory can defer costs inappropriately and overstate profit, while the normal capacity rule ensures that the cost of idle capacity hits the income statement when it occurs. This costing discipline is a core part of inventory accounting for production businesses and requires careful determination of normal capacity and the treatment of abnormal costs.

How does the lower of cost and net realisable value rule work?

ASC 330 requires inventory to be measured at the lower of its cost and net realisable value, except for inventory measured using LIFO or the retail inventory method, which uses the lower of cost or market. Net realisable value is the estimated selling price in the ordinary course of business less reasonably predictable costs of completion, disposal, and transportation. When net realisable value falls below cost — through obsolescence, damage, falling prices, or excess quantities — the inventory is written down to net realisable value, with the loss recognised in the period.

This rule ensures inventory is never carried at more than it can realistically be sold for, net of the costs to sell it. The assessment requires judgment about selling prices and selling costs, particularly for slow-moving or specialised inventory, and it should be performed regularly rather than only at year-end. For businesses with volatile inventory values or significant obsolescence risk, the lower of cost and net realisable value rule is a recurring source of write-downs that directly affect cost of goods sold and gross margin, making disciplined inventory valuation an important control.

How does inventory accounting affect the analysis of a business?

Inventory accounting decisions ripple through the analysis of any inventory-heavy business. The cost-flow method chosen — LIFO, FIFO, or weighted average — directly affects cost of goods sold, gross margin, reported profit, and the inventory value on the balance sheet, and these effects compound in periods of changing prices. A LIFO company reports lower margins and lower inventory than an otherwise identical FIFO company in a rising-price environment, while LIFO liquidations can temporarily inflate profit in ways unrelated to operations.

For analysts, this means inventory is one of the first areas to examine when comparing companies, especially across the US GAAP and IFRS divide where LIFO is permitted under one framework and banned under the other. Using the LIFO reserve to restate to a common basis, watching for liquidation effects, and understanding the write-down policy are all part of meaningful analysis. Inventory turnover, gross margin trends, and working capital all depend on these accounting choices, making inventory accounting central to understanding the financial performance of manufacturers, retailers, and distributors.

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