Inventory costing methods explained for small retailers

When the same product arrives at different prices, a shop has to decide which price each sold unit carried. The method you pick does not change how many units you sold or how many remain. It changes how the dollars split between cost of goods sold (COGS), which reduces profit, and ending inventory, which stays on the balance sheet. This guide works one fictional shop's quarter through the four common methods. It is not tax advice; ask your accountant which method suits your business.

Costing is an accounting choice, not shelf order

FIFO, LIFO and average cost each rest on a cost flow assumption: a rule for matching costs to sales on paper. None of them says which box a customer picks up. A grocer can put the oldest yogurt at the front and still value stock at an average. Physical order matters for freshness; the rotation planner sets a pick order by date received or by the date on the pack. Only specific identification follows the physical item, so every unit must be identifiable.

One fictional bike shop's quarter

A fictional bike shop stocks one commuter model, and each frame carries a serial number. Unit costs include inbound freight, which the shipment cost calculator spreads across a delivery. Costs are assigned at quarter end; costing each sale as it happens can change the LIFO and average figures.

The shop sold 12 bikes and had 8 left on March 31. Every method splits the same US$6,400 between those two groups.

FIFO: the oldest costs leave first

FIFO (first-in, first-out) treats the earliest units bought as the first sold. As a FIFO inventory example, the 12 bikes sold take the 5 opening bikes at US$300 and 7 February bikes at US$320, so COGS is US$1,500 + US$2,240 = US$3,740. The 8 left are 3 at US$320 and 5 at US$340, together US$2,660.

LIFO: the newest costs leave first

LIFO (last-in, first-out) treats the latest units bought as the first sold. The 12 bikes sold take all 5 March bikes at US$340 and 7 February bikes at US$320, so COGS is US$1,700 + US$2,240 = US$3,940. The 8 left are 3 at US$320 and 5 at US$300, together US$2,460. To adopt it for US tax, IRS Publication 538 says to file Form 970 with your return for the first year you use it.

The weighted average cost method

Every unit carries the same cost: total cost divided by total units, or US$6,400 ÷ 20 = US$320 a bike. COGS is 12 × US$320 = US$3,840, and the 8 on hand are worth US$2,560. Averaging smooths price swings and suits interchangeable goods bought often, such as screws, yarn or bottled drinks.

The specific identification method

Each unit keeps its own invoice cost, matched by serial number or another unique mark. Suppose the bikes sold were 2 opening bikes, 6 from February and 4 from March. COGS is US$600 + US$1,920 + US$1,360 = US$3,880, and the 8 left are 3 at US$300, 4 at US$320 and 1 at US$340, together US$2,520. It fits bikes, furniture or jewelry; for a shelf of identical candles it becomes guesswork.

How the four results compare

Like other inventory valuation methods, these four never change the US$6,400 total; they only move dollars between columns. At a fictional US$500 a bike, revenue is US$6,000 every time, yet gross profit differs by up to US$200. Turns shift too, since they use COGS; the turnover guide explains why the cost basis must stay consistent.

FIFO vs LIFO when prices rise

With rising prices, LIFO puts the newest, higher costs into COGS, which lowers reported profit and taxable income. FIFO does the reverse and leaves an ending figure close to current replacement cost. Pub 538 notes that the effect flips when prices fall. International standards narrow the choice. IAS 2 assigns cost by specific identification for items that are not interchangeable and by FIFO or weighted average for the rest. LIFO is not among them.

Lower of cost or market

When stock loses value, Pub 538 lets you compare each item's market value with its cost on the inventory date and use the lower one for US tax. It works item by item, not on the whole stock, and does not apply to goods valued under LIFO. Under IAS 2, financial statements use the lower of cost and net realizable value, the estimated selling price minus the costs to sell.

Which inventory method is best for a small business?

No method suits every shop, but some patterns hold.

• Specific identification for a few high-value pieces with serial numbers or unique tags.
• FIFO for most shops with interchangeable goods. It matches the order most shops try to sell in and is accepted under US tax rules and IAS 2.
• Weighted average for bulk goods bought often at shifting prices. Pub 538 does not list an average among its ways to identify cost, so ask your accountant before using one for tax.
• LIFO mainly where prices rise steadily and the tax effect justifies the extra rules.

Separately, Pub 538 lets small business taxpayers that meet a gross receipts test choose not to keep an inventory, though their method must still clearly reflect income. Whichever you choose, keep it consistent from year to year.

Can I change my inventory method?

Yes, with approval. IRS Publication 334 says changing how you figure inventory cost means filing Form 3115, Application for Change in Accounting Method, under either the automatic change or the advance consent procedures, and a user fee may apply. Talk to your accountant before the year of change, since a switch alters opening values and comparisons with earlier years.

Where Headoffis fits

Headoffis keeps unit quantities by product and location, changed by counts, receipts, transfers and reviewed sales. It does not hold cost layers, apply a costing method, or calculate cost of goods sold, stock value or profit; that work stays in your accounting software or with your accountant. The periodic and perpetual records guide explains how a counting routine feeds those figures.

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