MENTAL MODEL · M13079

Inventory Valuation Methods

SystemsHigh supportAccounting

Included

Updated 2026-08-11

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INTRODUCTION

English translation pending.

CORE DEFINITION

Inventory valuation methods determine which purchase costs are charged to cost of goods sold and which remain in ending inventory. Under first-in first-out, the oldest and usually cheapest costs are expensed first, leaving inventory close to replacement cost and pushing reported profit up during inflation. Under last-in first-out, the newest and most expensive costs are expensed first, lowering taxable profit and deferring taxes, while ending inventory stays at historical cost. The key qualification is that IFRS prohibits LIFO while United States GAAP permits it, so identical operations can report different results under the two frameworks, and any method change must be disclosed and applied consistently.

SCAFFOLDING EFFECT

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Reduce cognitive load

- Align the basis: confirm each firm's inventory method before comparing gross margins - Restore comparability: use the LIFO reserve to restate profit and inventory on one basis - Watch turnover: read inventory days to separate demand shifts from method changes

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Anchor fast decisions

Inventory bought in different periods carries different costs, and cost of goods sold must be drawn from some specific layer, so the choice of method directly changes reported profit. FIFO charges the older, cheaper layers first, leaving expensive inventory on the books and lifting both profit and assets during inflation. LIFO charges the newest, costliest purchases first, depressing profit and deferring taxes while ending inventory stays at historical cost. Because a method must be applied consistently and any change disclosed and restated, the choice becomes a clue about earnings quality.

MINIMUM ACTION

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Practice this model in one real situation:

Confirm from the accounting policy note whether the firm uses FIFO, LIFO or weighted average. 2. During inflation, compare its gross margin with peers using the other method. 3. Use the LIFO reserve, where disclosed, to restate profit and inventory onto a FIFO basis. 4. Track inventory days to judge whether a change came from demand or from a method switch. 5. If the method changed, recompute profit under the old basis and size the difference.

Check to track your progress (stored locally)

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Source support: Explicit

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mungermodels.comhttps://mungermodels.com/models/inventory-valuation-methodsZH · Explicit
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