Inventory

Learning Objectives

• Explain inventory as a consumable asset whose release rate is demand-driven, not time-driven
• Apply the cost flow assumptions (FIFO, LIFO, weighted average) and trace their effects on COGS, ending inventory, and net income
• Calculate ending inventory and COGS under periodic and perpetual systems
• Apply the lower of cost or net realizable value (NRV) rule and distinguish it from the LIFO/retail "lower of cost or market" rule
• Estimate ending inventory using the gross profit method and the retail inventory method
• Account for purchase commitments and LIFO liquidations

The Core Idea: Inventory as a Consumable Reservoir

Inventory is the purest example of a consumable asset — value that is depleted directly in production. Unlike equipment (which enables output without being consumed per unit) or cash (which sits until deployed), inventory flows through the entity at the pace of sales. Every unit sold drains the reservoir. Every purchase refills it. The balance sheet line item is a snapshot of what remains in the reservoir at a point in time.

The release mechanism is COGS: when a unit sells, its cost transfers from the balance sheet (Inventory) to the income statement (Cost of Goods Sold). The conservation equation holds perfectly — no value is created or destroyed. The entity exchanges inventory at cost for cash or receivables at selling price. The difference — gross profit — is the net wealth created by the transaction.

This is why the cost flow assumption matters so much. The question is not "which physical unit did we ship?" but "which cost layer do we assign to the units that left the reservoir?" The answer changes COGS, ending inventory, net income, and tax liability — all from the same physical transaction.

Cost Flow Assumptions

When identical goods are purchased at different prices over time, the entity must select a cost flow assumption to determine which costs drain from the reservoir into COGS and which remain in ending inventory. The assumption does not need to match physical flow — it is a cost allocation method.

FIFO (First-In, First-Out)

The oldest costs flow to COGS first. Ending inventory reflects the most recent purchase prices.

In rising prices: FIFO produces the highest ending inventory, lowest COGS, and highest net income. The balance sheet is more current (recent costs), but the income statement matches old costs against current revenues.

LIFO (Last-In, First-Out)

The most recent costs flow to COGS first. Ending inventory reflects the oldest purchase prices.

In rising prices: LIFO produces the lowest ending inventory, highest COGS, and lowest net income — providing a tax advantage. The income statement is more current (recent costs matched against current revenues), but the balance sheet is stale.

LIFO is permitted under U.S. GAAP but prohibited under IFRS. The LIFO conformity rule requires that if an entity uses LIFO for tax purposes, it must also use LIFO for financial reporting — one of the rare cases where tax and GAAP methods must align.

Weighted Average

A single average cost per unit is computed and applied uniformly.

Specific Identification

Each unit is tracked individually. Used for unique or high-value items (jewelry, automobiles, real estate). Not a cost flow assumption per se — it matches actual cost to actual unit.

Worked Example

A company has the following inventory data:

Total goods available: 450 units at a total cost of $5,500. During the month, 300 units were sold.

FIFO (300 sold):

• 100 units at $10 = $1,000
• 200 units at $12 = $2,400
• COGS = $3,400
• Ending inventory: 150 units at $14 = $2,100

LIFO (300 sold):

• 150 units at $14 = $2,100
• 150 units at $12 = $1,800
• COGS = $3,900
• Ending inventory: 100 at $10 + 50 at $12 = $1,600

Weighted Average:

• Average cost = $5,500 / 450 = $12.22/unit
• COGS = 300 x $12.22 = $3,667
• Ending inventory = 150 x $12.22 = $1,833

Notice: the same 300 physical units were sold. The only thing that changed was the cost assignment. LIFO COGS is $500 higher than FIFO — that difference flows straight to the bottom line and the tax return.

The COGS Equation

This is the fundamental identity for periodic inventory systems: Beginning Inventory + Purchases - Ending Inventory = COGS. It is a conservation equation — total goods available must either remain in inventory or have been sold. There is no third option (assuming no shrinkage, damage, or theft — which are separate write-down events).

Periodic vs. Perpetual Systems

Periodic system — Inventory counts and COGS are determined at period end. No running balance is maintained. Purchases go to a temporary Purchases account. COGS is computed as a plug: Beginning Inventory + Net Purchases - Ending Inventory (per physical count).

Perpetual system — Inventory and COGS are updated in real time with each transaction. The Inventory account is adjusted directly for every purchase and sale.

Key insight: Under FIFO, periodic and perpetual produce identical results — the oldest costs flow out first regardless of when you calculate. Under LIFO and weighted average, results differ because "most recent" and "average" depend on whether the calculation window is each transaction (perpetual) or the full period (periodic).

Lower of Cost or Net Realizable Value

Inventory is subject to a ceiling test — it cannot be reported above the amount the entity expects to recover from selling it. This is the conservatism principle in action: anticipate losses, do not anticipate gains.

The Two Regimes

The specific rule depends on the cost flow method:

This distinction is a common exam trap. The LIFO/retail rule uses a three-part "market" test:

• Ceiling: NRV (cannot exceed)
• Floor: NRV minus normal profit margin (cannot go below)
• Market: Current replacement cost, clamped between ceiling and floor

Compare the clamped replacement cost to historical cost. Use the lower amount.

Write-Down Mechanics

When NRV (or market, for LIFO) falls below cost:

• Write inventory down to the lower amount
• Recognize the loss in the current period (typically within COGS or as a separate loss line)
• The written-down value becomes the new cost basis
• Under U.S. GAAP, once written down, inventory cannot be written back up (IFRS permits reversal up to original cost)

Journal entry for write-down:

LIFO Reserve and LIFO Liquidation

The LIFO reserve is the difference between inventory under LIFO and what it would be under FIFO. It is disclosed in the footnotes and allows analysts to convert LIFO financial statements to FIFO for comparability.

LIFO liquidation occurs when units sold exceed units purchased, forcing the entity to dip into older, lower-cost LIFO layers. This artificially inflates gross profit and net income — the entity is reporting old costs against current revenues. Footnote disclosure is required when material.

Inventory Estimation Methods

When a physical count is impractical (fire loss, interim reporting), inventory can be estimated from financial data.

Gross Profit Method

The logic: if you know the historical gross profit percentage, you can estimate COGS from sales, and then back into ending inventory as the residual.

Worked example:

1. Goods available for sale = $50,000 + $200,000 = $250,000
2. Estimated COGS = $280,000 x (1 - 0.30) = $196,000
3. Estimated ending inventory = $250,000 - $196,000 = $54,000

The gross profit method is not acceptable for annual financial statements — it is an estimation technique for interim reporting, insurance claims, and reasonableness checks.

Retail Inventory Method

The retail method tracks goods at both cost and retail, computes a cost-to-retail ratio, and converts ending inventory at retail to an estimated cost.

Steps:

1. Calculate goods available at both cost and retail
2. Compute: Cost-to-Retail Ratio = Cost of Goods Available / Retail Value of Goods Available
3. Ending inventory at retail = Goods available at retail - Net sales
4. Ending inventory at cost = Ending inventory at retail x Cost-to-retail ratio

The ratio calculation varies by method:

Markups increase retail price above original retail. Markdowns decrease it below original retail. Net markups = markups - markup cancellations. Net markdowns = markdowns - markdown cancellations.

The conventional retail method (excluding markdowns) approximates lower of cost or market and is the most commonly tested version on the CPA exam.

Purchase Commitments

A purchase commitment is a noncancelable agreement to buy inventory at a specified future price. Under U.S. GAAP:

• If market value drops below the commitment price before delivery: recognize a loss and liability in the period the decline occurs
• When goods are received: record inventory at the lower market value
• If market value recovers before delivery: recognize a gain up to the previously recorded loss
• If market value equals or exceeds the commitment price: no entry — footnote disclosure only for material commitments

Losses on purchase commitments are recognized when they become probable, not when the goods arrive. This is the same conservatism principle that drives the lower of cost or NRV rule — anticipate losses, never gains.