Inventory Methods and What They Change

Canonical data. The sub-ledger illustration is the Meridian sensor line within Wexford Instruments, in $000; consolidated Wexford figures are USD millions. All figures agree with the Pillar 23 hub.

The units are indistinguishable, so there is no fact of the matter — and the answer determines cost of goods sold, gross profit, the inventory balance, and every ratio built from them. This is the cleanest demonstration in the whole pillar that reported figures are the product of conventions, because here the economics are held perfectly constant and the accounting still produces three different answers.

The three methods, and one distinction that prevents confusion

First, a point that trips up almost everyone: the cost-flow assumption has nothing to do with physical flow. A company using a first-in-first-out cost assumption is not claiming it ships the oldest units, and a grocer who physically rotates stock is not thereby required to use FIFO. These are accounting conventions for assigning costs, not descriptions of the warehouse.

FIFO assumes the earliest costs are charged first, leaving the most recent costs in the inventory balance. Weighted average pools all costs and charges the blended rate. LIFO assumes the most recent costs are charged first, leaving the oldest costs on the balance sheet — and it is permitted under US GAAP and prohibited under IFRS, which is one of the genuine substantive divergences between the two frameworks and a contrast with revenue recognition, where they converged.

What each method gets right, and what it gets wrong

When costs are rising, the methods diverge in a specific and symmetrical way — and the crucial point is that no method is correct on both statements at once.

FIFO produces a realistic balance sheet and a flattered income statement. The inventory balance holds recent costs, so it approximates what the stock would cost to replace today — genuinely useful. But cost of goods sold carries old, cheaper costs matched against today's selling prices, which inflates gross profit with what is really an inventory holding gain. On the illustration below, 20,000 of FIFO's reported gross profit is exactly that — a gain from having bought early, which the company must hand straight back when it replaces the stock at the new higher price. It is sometimes called phantom profit, and the name is fair: it is real in the accounts and unavailable to spend.

LIFO produces a realistic income statement and a stale balance sheet. Current costs are matched against current revenue, so the margin describes what the business is actually earning now — the better economic measure. The price is an inventory balance carrying costs that may be years or decades old and can bear no relation to replacement value. Weighted average sits between the two and gets neither exactly right, which is also a defensible position.

This is a genuine accounting dilemma rather than a loophole, and it is why standard-setters have reached different conclusions: the same information cannot be current on both statements simultaneously when costs move.

Worked example: the Meridian sensor line

A Wexford sub-ledger, in $000. Opening stock of 1,000 units at $100; purchases of 1,000 at $110 and 1,000 at $120. 2,000 units are sold for revenue of 300,000. Identical purchases, identical sales, identical cash in every column below.

The practical tools

Three things make this manageable rather than hopeless.

The LIFO reserve. US companies using LIFO must disclose the difference between their LIFO inventory and what it would be under FIFO. That single disclosure lets a reader convert a LIFO company's figures to a FIFO basis and compare like with like — it exists precisely because standard-setters recognised the comparability problem, and it is the most directly useful footnote in this article.

Methods must be applied consistently and changes disclosed. A company cannot switch method to suit a year's results without saying so; a change in accounting policy is a disclosed event with its effect stated.

And inventory is written down when it is worth less than cost. Both frameworks require carrying inventory at the lower of cost and its realisable value, so obsolete or unsellable stock is charged against profit. Here the frameworks diverge again: IFRS permits a write-down to be reversed if the value recovers, while US GAAP generally does not — a different asymmetry from goodwill impairment, where reversal is prohibited under both.

Wexford itself carries inventory of 130.0 against cost of goods sold of 600.0, giving turnover of 4.62× and 79.1 days of inventory. Those figures are only comparable to another company's if both use the same method — which is the entire practical lesson.