Inventory is often the biggest current asset a retailer owns, and it is counted by people walking aisles with scanners. Miss one pallet in the back room, or count a shelf twice, and the error does not stay in the inventory account. Ending inventory is subtracted to find cost of goods sold, so a counting mistake flows straight into gross profit, net income and owner's equity. And because this year's ending inventory becomes next year's beginning inventory, the same mistake shows up again a year later, in the opposite direction. This lesson traces that chain, then looks at the tools businesses use to stop it from happening: technology that tracks every unit, and internal controls that keep inventory and its records honest.
How an ending inventory error flows through two years
Ending inventory has a minus sign in front of it. So if ending inventory is overstated by $3,000, cost of goods sold is understated by $3,000, and gross profit and net income are overstated by $3,000. On the balance sheet, assets (inventory) are overstated by $3,000 and so is equity, because the extra net income was closed into Capital (or Retained Earnings for a corporation). Next year, that same inflated figure is beginning inventory, which has a plus sign: cost of goods sold is overstated by $3,000 and net income understated by $3,000. By the end of the second year the two errors cancel, so the error is called self-correcting. It still matters: both years' statements were wrong, and anyone comparing the two years sees a false drop in profit.
| 2026 correct | 2026 reported | 2027 correct | 2027 reported | |
|---|---|---|---|---|
| Sales | $100,000 | $100,000 | $110,000 | $110,000 |
| Beginning inventory | $12,000 | $12,000 | $15,000 | $18,000 |
| Purchases | $60,000 | $60,000 | $65,000 | $65,000 |
| Cost of goods available | $72,000 | $72,000 | $80,000 | $83,000 |
| Ending inventory | $15,000 | $18,000 | $14,000 | $14,000 |
| Cost of goods sold | $57,000 | $54,000 | $66,000 | $69,000 |
| Gross profit | $43,000 | $46,000 | $44,000 | $41,000 |
| Operating expenses | $25,000 | $25,000 | $27,000 | $27,000 |
| Net income | $18,000 | $21,000 | $17,000 | $14,000 |
| Ending inventory OVERSTATED in Year 1 | Year 1 | Year 2 |
|---|---|---|
| Cost of goods sold | Understated | Overstated |
| Gross profit and net income | Overstated | Understated |
| Assets (inventory) at year end | Overstated | Correct |
| Owner's equity at year end | Overstated | Correct |
Technology in inventory management
- Barcodes: every product carries a code (such as a UPC) that is scanned on receiving and at the till, so the system knows exactly which item moved, without anyone typing it.
- RFID (radio-frequency identification) tags: small chips read by radio, without a line of sight. A handheld or doorway reader can count a whole rack or carton in seconds, which makes frequent counts practical.
- Point-of-sale (POS) systems: each sale updates the perpetual records immediately, recording revenue, HST, cost of goods sold and the reduction in inventory at once.
- Perpetual tracking across locations: managers see stock in every store and warehouse, so goods can be moved to where they will sell instead of being marked down.
- Reorder alerts: when units on hand fall to the reorder point, the system flags or automatically creates a purchase order.
- Cycle counts and exception reports: software schedules small counts through the year and highlights items whose records and counts disagree.
For example, if Northshore sells 12 water bottles a day, the supplier takes 5 days to deliver, and the store wants a cushion of 20, the system reorders when stock falls to bottles. Good tracking also lets managers watch inventory turnover, : how many times a year the average stock is sold and replaced. Higher turnover means less cash tied up in goods sitting on shelves. Technology does not remove the need for a physical count, though. A perpetual record only shows what SHOULD be there; the count shows what IS there, and the difference is shrinkage (theft, damage, spoilage or recording errors), recorded as debit Cost of Goods Sold, credit Merchandise Inventory.
Internal control over inventory
Internal control is the set of policies and procedures a business uses to safeguard its assets, make its records reliable, and ensure that rules are followed. Inventory needs strong control because it is valuable, portable, and easy to resell. The controls below work together; none is enough on its own.
| Control | What it means for inventory | What it prevents |
|---|---|---|
| Separation of duties | Different people order goods, receive goods, record them, and approve payment | One person stealing goods and hiding it in the records |
| Authorization | Purchases need an approved purchase order; write-offs and price changes need a manager's approval | Unneeded or fictitious purchases |
| Prenumbered documents | Purchase orders, receiving reports and invoices are numbered in sequence and every number is accounted for | Missing or duplicate documents going unnoticed |
| Paper (audit) trail | Every unit can be traced from purchase order to receiving report to supplier invoice to payment | Paying for goods never ordered or never received |
| Physical counts | Regular full counts or cycle counts, compared with the perpetual records by someone who does not handle the stock | Shrinkage hiding behind the records |
| Physical safeguards | Locked storerooms, limited access, cameras, security tags | Theft and damage |