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Inventory Systems and Inventory Costing Methods | Principles of Accounting

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Calculating Accurate Inventory Costs

Course Hero’s accounting module “Inventory Systems and Inventory Costing Methods” breaks down two decisions that sit at the center of every retailer’s books: how often to track stock, and how to price it once it’s sold. The lesson, part of the Principles of Accounting series, walks through the perpetual and periodic tracking systems before moving into the cost flow assumptions — FIFO, LIFO, and weighted average — that determine what shows up on the balance sheet and the income statement.

• Perpetual systems update inventory and cost of goods sold in real time using point-of-sale terminals, barcode scanners, and inventory software, but still require periodic physical counts to catch shrinkage.
• Periodic systems rely on manual counts done weekly, monthly, or annually — cheaper to run but blind to inventory levels between counts.
• FIFO assumes the oldest goods are sold first, LIFO assigns the newest costs to sales, and weighted average splits total inventory cost across all units on hand.

Perpetual Tracking Versus the Periodic Count

The perpetual method is the system most shoppers never think about but interact with constantly. Every scan at checkout adjusts the stock count and books the cost of goods sold instantly, which is why a retailer running perpetual inventory can pull an accurate on-hand figure at any moment without shutting down to count boxes. The tradeoff is that the automation doesn’t catch theft, breakage, or clerical errors on its own — the lesson notes that even a fully perpetual operation still needs occasional physical audits to true up the books against shrinkage.

The periodic system flips that tradeoff. A small operation using periodic counting doesn’t touch its inventory records between counts — no live COGS figure, no real-time stock level — but it also doesn’t need barcode scanners or inventory software to run. For a shop with a handful of SKUs, a monthly or annual count can be the more sensible way to manage stock without the overhead a perpetual system demands.

Assigning Cost When Prices Move

Once a business decides how often to count inventory, it still has to decide what each unit sold actually cost — and that’s rarely as simple as looking at a receipt, since the same item is often bought at different prices over time. That’s where the cost flow assumptions come in.

Under FIFO, the oldest goods purchased are treated as the first ones sold — cost of goods sold reflects yesterday’s prices, even while the shelf reflects today’s.

FIFO (First-In, First-Out) assumes the earliest inventory purchased moves out the door first, so the cost of goods sold is built from older, typically cheaper purchases while the ending inventory on the balance sheet reflects the newest, often pricier stock. LIFO (Last-In, First-Out) runs the opposite direction, pulling the cost of the most recent purchases into COGS — a method that can shrink reported profits and taxable income when prices are climbing, since the newer, higher costs get expensed first. Weighted Average Cost skips the ordering assumption entirely, dividing the total cost of inventory available by the total units available to produce one blended per-unit cost applied across the board.

Method Selection Impacts Financial Reporting

None of this is academic bookkeeping trivia — the choice between FIFO, LIFO, and weighted average changes the numbers a business reports to lenders, investors, and the IRS. A company sitting on inventory bought before a price spike will show a leaner cost of goods sold and fatter gross profit under FIFO than it would under LIFO, while the balance sheet valuation of what’s left in the warehouse moves in the opposite direction. That single choice ripples into taxable income, loan covenants tied to profitability, and how a company’s margins compare against competitors using a different method — which is exactly why the lesson frames costing method selection as a decision with real operational and reporting consequences, not just a bookkeeping formality for anyone sourcing and pricing products to sell.

The mechanics stay the same whether it’s a corner hardware store running periodic counts by hand or a warehouse operation with barcode scanners tied into perpetual software — pick the tracking frequency that fits the operation’s size, then pick the costing method that fits how prices are moving, because both decisions land directly on the bottom line before a single unit changes hands again.