Inventory and Cost of Goods Sold

Why inventory is where profit and fraud both hide

A regional sporting-goods chain, HarborLine Outfitters, reports $94 million in revenue and a healthy gross margin. The board approves a second warehouse expansion. Six months later, auditors find $3.2 million of slow-moving ski jackets carried at full cost on the balance sheet, a perpetual inventory system that has not been reconciled to physical counts in eleven months, and a COGS (cost of goods sold, the inventory cost of what was sold) calculation that switched from FIFO (first in, first out, selling oldest inventory costs first) to weighted average mid-year without clear disclosure. Gross margin looked stable. The product economics did not.

Inventory is one of the largest balance-sheet items for retailers and manufacturers, and one of the easiest places for numbers to drift from economic reality. Unlike cash, you cannot call the bank to verify it. Unlike accounts receivable (customer amounts owed, covered in Unit 4 Lesson 2), you cannot send a confirmation letter. Inventory sits in warehouses, stores, and factory floors, moving constantly, subject to damage, theft, obsolescence, and counting error. Management chooses how to assign costs when identical items were purchased at different prices. Those choices flow directly into COGS, gross margin, taxable income, and loan covenant compliance.

If you completed Unit 1 (The Accounting Equation, Assets, Liabilities, and Equity), you know inventory is a current asset: economic value the company expects to convert to cash or use up within a year. If you completed Unit 3 (Expense Recognition and Matching), you know purchasing inventory is not an immediate expense under accrual accounting (recording revenue when earned and expenses when incurred, not when cash moves). The expense waits until sale. This lesson teaches the full mechanics between those two ideas: how inventory is measured, how cost moves to the income statement, how managers and investors should read the result, and what goes wrong when controls fail.

The managerial question is not "how do I count boxes." It is: "Do our reported margins reflect what we actually paid for what we sold, and is the inventory on our balance sheet still worth what we say it is?"

Inventory as a balance-sheet asset

Inventory is goods a company holds for sale in the ordinary course of business. For a retailer like HarborLine, inventory is jackets, boots, and camping gear sitting on shelves and in distribution centers. For a manufacturer like NorthPeak Manufacturing (a fictional producer of camp stoves), inventory appears in three layers: raw materials (steel, valves, packaging), work-in-process or WIP (partially assembled units on the factory floor), and finished goods (completed stoves ready to ship).

Inventory meets the definition of an asset from Unit 1 because the company controls it and expects future economic benefit. That benefit arrives when a customer buys the product and the company collects cash or records a receivable. Until then, the cost of those goods stays on the balance sheet (the snapshot of what a company owns and owes at a date), not on the income statement (profit and loss over a period, also called the P&L).

This timing distinction confuses beginners who track cash closely. Suppose HarborLine buys $500,000 of winter coats in September, pays cash, and sells only half by December 31. Under accrual rules from Unit 3 Lesson 1 (Cash Accounting versus Accrual Accounting), September shows a $500,000 cash outflow on the statement of cash flows, but only half of that cost becomes COGS on the income statement by year-end. The other half remains inventory on the balance sheet. A manager who treats the full $500,000 as "September expense" will understate profit in the purchase month and overstate it when the remaining coats sell in January.

From Unit 2 (Journal Entries, Debits and Credits), the purchase of inventory on credit is recorded by debiting (increasing) Inventory and crediting accounts payable (AP, amounts owed to suppliers). Cash purchase debits Inventory and credits Cash. No expense is recognized at purchase. The debit to Inventory increases total assets; if paid with cash, assets stay level overall (Inventory up, Cash down). If purchased on credit, assets and liabilities both rise. The accounting equation (Assets = Liabilities + Equity) still balances.

Investors and lenders watch inventory because it ties up working capital. From Unit 4 Lesson 1 (Cash and Internal Controls), weak controls over inventory create shrinkage risk (loss from theft, damage, and recording errors). A company can report strong revenue growth while silently building a warehouse full of goods that will never sell at full price. The balance sheet looks asset-rich; the future income statement will absorb the disappointment through write-downs and markdowns.

COGS, gross profit, and gross margin

When inventory is sold, its cost leaves the balance sheet and becomes COGS on the income statement. This is the clearest application of the matching principle from Unit 3 Lesson 3 (Expense Recognition and Matching): the cost of the unit sold is recognized in the same period as the revenue from that sale.

Gross profit equals sales revenue minus COGS. Gross margin equals gross profit divided by sales revenue, usually expressed as a percentage. These metrics sit at the top of the income statement and drive decisions in retail, manufacturing, consumer products, and any business with a physical or digital product catalog.

The COGS formula for a merchandising company using a periodic inventory system (explained in the next section) is:

COGS = Beginning inventory + Purchases − Ending inventory

Read this formula in plain language. Start with what you had at the beginning of the period. Add what you bought (or manufactured) during the period. That sum equals cost of goods available for sale. Subtract what remains on hand at period end. What is left is the cost of what was sold.

Check logic: Beginning inventory + Purchases = Ending inventory + COGS. The goods available must either remain in the warehouse or have been sold.

COGS is not a single purchase invoice. It is a flow calculated over a period. A merchandising manager who negotiates a 4% supplier discount on next month's purchase does not improve this month's COGS unless those specific units are sold this month. A manufacturing manager who reduces factory scrap by 2% affects future COGS when the improved units sell. Gross margin is where product-level economics first become visible before SG&A (selling, general, and administrative expenses: rent, marketing, executive salaries) and other operating costs.

Analysts compare gross margin across competitors to judge pricing power and sourcing efficiency. A lender reviewing a retail borrower watches gross margin compression as an early warning: if COGS is rising faster than selling prices, cash flow will tighten even before the company misses a covenant. A board member should ask whether margin changes reflect real cost improvements, price increases, or accounting method changes. The third explanation is common and easy to miss.

HarborLine sells a jacket for $65. If COGS for that jacket is $32 under FIFO during a period of rising purchase costs, gross profit is $33 and gross margin is 50.8%. If the same jacket has a COGS of $38 under LIFO (last in, first out, selling newest inventory costs first), gross profit is $27 and gross margin is 41.5%. Same store, same register receipt, different accounting cost flow assumption. The customer paid $65 either way. The shareholder's picture of product profitability changes.

Perpetual versus periodic inventory systems

Companies track inventory quantities and costs using one of two broad systems. The choice affects how often the books are updated, what technology is required, and how shrinkage is detected.

Perpetual inventory system: The accounting system updates Inventory and COGS at each sale (and each purchase). Modern ERP (enterprise resource planning) systems at retailers and distributors typically run perpetual records. When HarborLine scans a bar code at checkout, the system records sales revenue, reduces inventory quantity, and records COGS in real time.

Periodic inventory system: The company does not update inventory balances at each sale. Instead, it counts inventory physically at period end (or relies on cycle counts aggregated quarterly) and computes COGS using the formula above. Purchases during the period are recorded in a Purchases account or directly in Inventory without tracking running quantities at the SKU (stock keeping unit, an individual product code) level.

Neither system changes the economics. Both must end with the same total COGS for the period if counts are accurate and methods are consistent. The perpetual system simply makes COGS visible throughout the period and forces earlier detection of shrinkage.

Under perpetual, a sale of one jacket with a assigned cost of $32 produces:

The first pair records revenue under accrual rules from Unit 3 Lesson 2 (Revenue Recognition). The second pair matches expense to revenue. From Unit 2, COGS is an expense account (debit increases it), Inventory is an asset account (credit decreases it). Net effect on assets: if cash sale, Cash up $65 and Inventory down $32, net assets up $33 (gross profit). Equity rises through retained earnings when the books close.

Under periodic, the sale records only revenue and the receivable or cash:

At period end, after a physical count, an adjusting entry transfers the total cost of goods sold:

Operators prefer perpetual because store managers can see on-hand quantities daily. Controllers prefer perpetual because year-end surprises shrink. Lenders often ask whether inventory is perpetual and how often physical counts confirm the records. A perpetual book that never gets counted is perpetual in name only.

Cost flow assumptions: FIFO, LIFO, and weighted average

When identical SKUs are purchased at different costs over time, which cost leaves inventory when a unit is sold? GAAP (Generally Accepted Accounting Principles, the official U.S. rulebook for financial statements) requires a consistent cost flow assumption. Note the careful language: accounting tracks cost flows, not necessarily physical flows. A grocery store physically sells older milk first. It may still use a weighted-average cost for financial reporting if that method is applied consistently and disclosed.

Three methods dominate managerial and financial reporting conversations:

FIFO (first in, first out): Assign the oldest purchase costs to COGS first. Ending inventory reflects the most recent purchase costs. In periods of rising costs (inflation in product inputs), FIFO produces lower COGS and higher reported gross margin than LIFO. The balance sheet inventory value is closer to current replacement cost.

LIFO (last in, first out): Assign the newest purchase costs to COGS first. Ending inventory reflects older, often lower, costs. In rising cost environments, LIFO produces higher COGS, lower reported gross margin, and lower taxable income. IFRS (International Financial Reporting Standards, the rulebook used in most countries outside the U.S.) prohibits LIFO. U.S. GAAP allows it. The U.S. LIFO conformity rule requires companies that use LIFO for tax to also use LIFO in financial statements. Many U.S. retailers use FIFO for books; many U.S. manufacturers and wholesalers with volatile input costs have historically used LIFO for tax timing.

Weighted average: Compute an average cost per unit from all units available and apply that average to both COGS and ending inventory. Produces results between FIFO and LIFO in inflationary periods. Common in manufacturing with continuous production and in commodity-like inventories.

Specific identification tracks the actual cost of each individual unit. It is appropriate when units are unique: vehicles with serial numbers, custom jewelry, high-value real estate lots. HarborLine's mass-produced fleece jackets are not tracked this way.

Managers must choose a method and stick with it. Switching from FIFO to LIFO without justification is a red flag. Footnotes in the 10-K (annual filed report with audited financials) disclose the method. When comparing two competitors, an analyst who ignores different inventory methods compares margins that are not economically comparable.

Consider a simple illustration before the full worked examples. NorthPeak has 100 stoves in inventory purchased at $10 each, then buys 100 more at $14 each. Total: 200 units, $2,400 cost. It sells 100 stoves. Revenue is irrelevant for the cost assignment.

• FIFO COGS: 100 units at $10 = $1,000. Ending inventory: 100 at $14 = $1,400. Check: $1,000 + $1,400 = $2,400 ✓
• LIFO COGS: 100 units at $14 = $1,400. Ending inventory: 100 at $10 = $1,000. Check: $1,400 + $1,000 = $2,400 ✓
• Weighted average: Average cost = $2,400 / 200 = $12 per unit. COGS = 100 × $12 = $1,200. Ending = 100 × $12 = $1,200. Check: $1,200 + $1,200 = $2,400 ✓

Same units sold. COGS differs by $400 between FIFO and LIFO. At a 25% tax rate, that is $100 of tax timing difference in a single layer example. Across billions in inventory, method choice is a strategic tax and earnings management conversation, not a footnote.

Lower of cost or net realizable value (LCNRV)

Assets should not be reported above amounts the company can recover. For inventory, GAAP applies the lower of cost or net realizable value rule, often abbreviated LCNRV or described as "lower of cost or market" in older materials. NRV (net realizable value) is the estimated selling price in the ordinary course of business minus reasonably predictable costs to sell and complete.

If jackets cost $40 each but can only be sold for $25 after a season-end clearance (and selling costs are minimal), carrying them at $40 overstates both inventory and future gross margin. The company writes inventory down to $25. The other $15 hits the income statement.

Typical journal entry:

Some companies use a separate loss account for clarity in management reporting. The debit is an expense in the period of the write-down, not when the item eventually sells. This is an application of conservatism (recognize losses when probable, gains when realized) consistent with Unit 3 Lesson 4 (Adjusting Entries).

Retailers take write-downs after holidays when seasonal goods missed plan. Manufacturers write down obsolete parts when a product line is discontinued. Lenders read sudden inventory write-downs as signals that prior gross margins were overstated. Investors ask whether the write-down is a one-time cleanup or evidence of chronic bad buying.

GAAP generally does not allow write-ups after a write-down for the same goods (reversal is limited). If you wrote jackets down to $25, you do not later restore them to $40 if fashion trends recover. That asymmetry pushes management to delay write-downs until pressure builds, another reason auditors focus on inventory aging schedules.

Shrinkage, physical counts, and internal control

Shrinkage is inventory loss from theft (shoplifting, employee theft, vendor fraud), damage, spoilage, and administrative errors (recording the wrong quantity, mislabeling SKUs). Every retailer and warehouse operator plans for some shrinkage; the accounting question is whether it is measured and recorded.

Under a perpetual system, shrinkage is revealed when physical count is less than book quantity:

Shrinkage cost = (Book quantity − Physical quantity) × Unit cost

The journal entry typically debits COGS (or a separate shrinkage expense account) and credits Inventory.

Under a periodic system, shrinkage is invisible separately unless management computes it. The period-end COGS formula absorbs missing units automatically: ending inventory is lower than expected, so COGS is higher. A store manager who never investigates may blame "tough comps" on the income statement when the real issue is theft at the loading dock.

From Unit 4 Lesson 1, strong internal controls include segregation of duties (receiving clerks different from record keepers), camera coverage, cycle counts of high-shrink SKUs, and investigation thresholds when variances exceed policy. HarborLine's eleven-month failure to reconcile perpetual records to physical counts is a control failure first and an accounting problem second.

Controllers often express shrinkage as a percentage of sales or of inventory cost. A move from 1.8% to 2.4% looks small until you apply it to $200 million in revenue: $1.2 million of profit walked out the door. Gross margin analysis that ignores shrinkage teaches the wrong lesson about pricing and sourcing.

Manufacturing inventory and overhead allocation

NorthPeak illustrates a cost flow beyond simple purchase-and-resell. Manufacturing COGS includes direct materials, direct labor, and manufacturing overhead (factory rent, utilities, depreciation on equipment, indirect labor). Materials and labor that can be traced to units are product costs and sit in WIP until units are finished, then in finished goods until sold.

Overhead allocation assigns indirect factory costs to inventory using a systematic base (machine hours, labor hours, units produced). GAAP expects allocation based on normal capacity (expected sustainable production volume), not maximum theoretical output. Costs from abnormal idle capacity (a plant shutdown due to a strike, not routine maintenance) are often expensed immediately rather than capitalized into inventory, so current period profit bears the pain.

When NorthPeak completes 800 stoves at a total production cost of $48,000, finished goods inventory rises by $48,000 and WIP and related accounts decrease correspondingly. COGS is recorded only when stoves are sold. This links back to Unit 3: buying steel is not expense; selling the stove is when the accumulated product cost becomes COGS.

Managers in manufacturing watch inventory turnover (COGS divided by average inventory) and days inventory outstanding (365 divided by turnover) to see whether capital is trapped in unsold units. Low turnover relative to peers may mean weak demand, production running ahead of sales, or overstated unit costs from poor overhead allocation.

HarborLine Outfitters operates twelve outdoor apparel stores in the Pacific Northwest. The controller closes the books quarterly. HarborLine uses a periodic inventory system and counts all locations during the last week of each quarter. Management is evaluating whether to refinance a line of credit; the bank wants trailing gross margin under consistent accounting. The CFO pulls Q1 data for a single SKU family, the RidgeShell jacket, to illustrate how cost flow assumptions change reported margins even when selling prices are stable.

Part A: Setup and goods available

RidgeShell jacket, Q1 2025 (January 1 through March 31)

Sales during Q1: 1,450 jackets at $65 each (net of returns).

Physical count March 31: 450 jackets on hand.

Cost of goods available for sale:

Revenue check: 1,450 × $65 = $94,250 net sales.

The units reconcile: 1,900 available − 1,450 sold = 450 ending. The dollar total of $63,900 must equal COGS plus ending inventory under any method. That identity is our anchor check.

Part B: FIFO, LIFO, and weighted average COGS

FIFO: COGS uses the oldest layers first.

Ending inventory under FIFO is what remains, all from the newest layers:

Check: $46,950 + $16,950 = $63,900 ✓

LIFO: COGS uses the newest layers first.

Ending inventory under LIFO:

Check: $50,300 + $13,600 = $63,900 ✓

Weighted average: One average cost applies to all units.

Average unit cost = $63,900 ÷ 1,900 units = $33.6316 per unit (carried to four decimals for rounding).

Check: $48,766 + $15,134 = $63,900 ✓

COGS differs by $3,350 between FIFO and LIFO ($50,300 − $46,950). Same stores, same jackets sold, same customer prices.

Part C: Gross margin comparison and balance sheet impact

Gross profit formulas: $94,250 − COGS.

Gross margin formulas: Gross profit ÷ $94,250.

Under rising purchase costs, FIFO makes current-quarter product economics look strongest. LIFO makes them look weakest. Weighted average smooths the story.

On the balance sheet at March 31, inventory is $16,950 (FIFO), $13,600 (LIFO), or $15,134 (weighted average). A lender computing the current ratio (current assets ÷ current liabilities) or tangible net worth sees different collateral coverage depending on method. None of these numbers equals the replacement cost of reordering 450 jackets in April (likely near $38 each, or $17,100). Inventory valuation is accounting measurement, not a perfect market quote.

Part D: Managerial read

The bank's credit officer asks three questions HarborLine's board should rehearse:

1. Which method do we use for financial statements, and has it changed? Switching to weighted average mid-year without disclosure would make Q1 margins non-comparable to prior years.

2. Does reported gross margin reflect replacement cost? In inflation, FIFO gross margin may overstate sustainable economics because COGS reflects older, cheaper layers. Merchandising may need price increases even when reported margin looks flat.

3. Is ending inventory overstated? If RidgeShell jackets are moving slower than plan and clearance will be needed, LCNRV testing may be required before the bank closes. Carrying $16,950 at FIFO cost when NRV is $28 per jacket (450 × $28 = $12,600) would trigger a $4,350 write-down.

The operator takeaway: cost flow method is a policy choice with real earnings and tax effects. The investor takeaway: read the inventory footnote before comparing HarborLine to a LIFO-based competitor. The controller takeaway: document assumptions and run the same method every quarter unless GAAP requires a change with retrospective disclosure.

NorthPeak Manufacturing builds portable camp stoves sold through outdoor retailers. It uses a perpetual inventory system with weighted average costing in finished goods. April activity below shows how production adds layers, how sales pull cost into COGS continuously, and how period-end events (shrinkage and obsolescence) become expenses.

Part A: Beginning balance and April production

Finished goods, camp stove Model T-400, April 2025

April production completed and transferred to finished goods:

After transfer, perpetual records show two cost layers before any sales:

Weighted average unit cost after production = $57,000 ÷ 1,000 = $57.00 per unit.

Part B: April sales and perpetual COGS

NorthPeak sold 750 units in April at $95 each.

Perpetual COGS at sale (weighted average): 750 × $57.00 = $42,750

Journal entries at each sale (summary for the month):

Revenue check: 750 × $95 = $71,250.

Book inventory after sales:

Check: $57,000 − $42,750 = $14,250 ✓

April gross profit before adjustments: $71,250 − $42,750 = $28,500.

Gross margin: $28,500 ÷ $71,250 = 40.0%.

Part C: Physical count, shrinkage, and LCNRV write-down

Physical count April 30: 235 units (15 units short of book).

Shrinkage cost: 15 × $57.00 = $855

Inventory after shrinkage: 235 × $57.00 = $13,395. Check: $14,250 − $855 = $13,395 ✓

Obsolescence review: Of the 235 units, 40 units are an older T-400 colorway. NorthPeak estimates they can be sold for $48 each with $8 per unit in selling costs.

NRV per unit = $48 − $8 = $40.

Historical cost per unit = $57.

LCNRV per unit = lower of $57 or $40 = $40.

Write-down = 40 × ($57 − $40) = 40 × $17 = $680

Final inventory April 30:

Check: $13,395 − $680 = $12,715 ✓

Part D: April income statement impact and stakeholder read

Without shrinkage and write-down, gross margin was 40.0%. The 2.2-point drop is entirely operational and measurement, not selling price.

Investor read: A quarter with a large write-down is not always a one-time event. Ask whether buying, production planning, or controls failed. NorthPeak's shrinkage of 15 units on 1,000 available (1.5% of flow) may be acceptable, but the pattern matters if repeated.

Lender read: Inventory collateral value for a borrowing base certificate should use net inventory after LCNRV, not gross historical cost. $12,715 is the relevant finished-goods figure, not $14,250.

Operator read: Perpetual records forced early visibility. Production managers see that building obsolete colorways converts $57 cost into $40 recoverable value. Merchandising and operations should align on minimum order quantities and end-of-life plans before the factory runs extra batches.

Summit Trail Supply is a fictional online retailer of hiking equipment. It uses a periodic system and counts inventory on December 31. Data for TrekLite boots for the year:

Sales for the year: 340 units at $110 each.

Physical count December 31: 110 units on hand.

Tasks:

1. Compute cost of goods available for sale (units and dollars).
2. Compute COGS and ending inventory under FIFO, LIFO, and weighted average.
3. Compute gross profit and gross margin under each method.
4. Management discovers 20 units in ending inventory are last season's color and NRV is $55 per unit (selling price $60 minus $5 selling costs). All other ending units have NRV above cost. Compute the LCNRV write-down under FIFO ending inventory and the inventory balance after write-down.
5. Explain in a short paragraph why a lender might care more about ending inventory than COGS when collateralizing a line of credit.

Solution

1. Goods available

Unit check: 450 − 340 sold = 110 ending ✓

2. COGS and ending inventory

FIFO (oldest costs leave first):

Ending FIFO:

Check: $18,760 + $6,820 = $25,580 ✓

LIFO (newest costs leave first):

Ending LIFO:

Check: $19,960 + $5,620 = $25,580 ✓

Weighted average:

Average unit cost = $25,580 ÷ 450 = $56.8444 per unit (carried to four decimals for rounding).

Check: $19,327 + $6,253 = $25,580 ✓

3. Gross profit and gross margin

Revenue = 340 × $110 = $37,400.

4. LCNRV write-down (FIFO ending)

FIFO ending is 110 units at $62 = $6,820 historical cost.

20 units have NRV $55; cost $62. LCNRV per unit = $55. Write-down = 20 × ($62 − $55) = $140.

After write-down:

Check: $6,820 − $140 = $6,680 ✓

5. Why lenders focus on ending inventory

A lender collateralizing a line of credit cares about what the company holds right now that can be liquidated if the loan defaults, not the historical cost of what already sold during the year. COGS tells the income statement story of past sales; ending inventory (net of LCNRV write-downs) approximates the asset pool available as security. Overstated ending inventory inflates borrowing capacity; obsolete stock written down to NRV reduces the advance rate realistically. Internal control over counts and markdown policy therefore affects credit availability as directly as it affects gross margin.

Cascade Home Goods uses a perpetual FIFO system for kitchenware. Only one SKU matters for this problem: CeramicMix bowls.

Tasks:

1. Show the FIFO layers remaining after each purchase and sale (units and costs).
2. Compute total COGS for March and ending inventory at March 31.
3. Verify: Beginning + Purchases = Ending + COGS.
4. Compute March gross profit and gross margin on this SKU.

Solution

1. Layer walk (perpetual FIFO)

After Mar 8 purchase:

Mar 15 sale of 120 units (oldest first):

Remaining after sale:

After Mar 22 purchase:

Mar 28 sale of 50 units:

Remaining after sale:

2. March totals

3. Reconciliation

Check: $2,180 = $2,180 ✓

4. Gross profit and gross margin

Revenue = (120 + 50) × $22 = 170 × $22 = $3,740.

Gross profit = $3,740 − $1,480 = $2,260.

Gross margin = $2,260 ÷ $3,740 = 60.4%.

Perpetual FIFO assigns the same total COGS as periodic FIFO would for March if the same layers and sales occurred, but perpetual records $1,020 at March 15 and $460 at March 28 rather than one lump-sum adjustment at month end.

Key takeaways

• Inventory is a current asset at historical cost until sold; COGS is the matching expense that records the cost of units sold in the same period as revenue.
• The COGS formula (Beginning + Purchases − Ending) must reconcile: goods available equal ending inventory plus COGS, and every method must respect that identity.
• FIFO, LIFO, and weighted average are policy choices that change gross margin and ending inventory in inflation, especially when comparing companies across methods.
• Perpetual systems update COGS at each sale and expose shrinkage when counts differ from books; LCNRV write-downs prevent carrying obsolete inventory above recoverable value.

1. Pick a retailer or manufacturer you follow (or your own employer). Find its inventory accounting method in the annual report footnotes. Is it FIFO, LIFO, or weighted average? Did inventory grow faster than sales over the last two years?
2. A controller proposes switching from FIFO to weighted average to "smooth earnings." What questions should the board ask about comparability, tax, and disclosure?
3. Continue to Lesson 4: Property, Plant, Equipment, and Depreciation.