Weighted average or FIFO? Choosing a costing method for a trading company

Why does the costing method matter?

The costing method decides what each unit you sell cost you, when identical units were bought at different prices. A trading company buys the same item many times a year, and the price moves with suppliers, currencies and commodities. The units on the shelf look the same. The method decides which price goes to cost of sales and which stays in stock.

That choice flows straight into the numbers people care about:

• gross margin on every invoice and in every monthly report;
• closing stock value on the balance sheet;
• how stable margins look from month to month;
• how much work your stock records and reconciliations take.

It doesn’t change the cash you paid. Over the life of the stock, every method charges the same total cost. It changes when that cost reaches the profit and loss account.

How do weighted average and FIFO work?

Both methods start from the same receipts. They differ in how a sale picks its cost.

FIFO assumes the oldest stock is sold first. Each receipt forms a cost layer; a sale uses up the oldest layer before touching the next. The stock left at the end is valued at the most recent purchase prices.

Weighted average cost blends every unit of an item into one average cost. IAS 2 describes two ways to calculate it: on a periodic basis, or as each additional shipment is received. The second is often called a moving or running average. A system that costs each sale as it happens uses the moving average, because the period hasn’t ended yet.

Neither method needs to match how your storekeepers actually pick. They are cost formulas, not picking rules.

Weighted average vs FIFO: a worked example

Here is one month for one fictional item, a ½-inch brass ball valve, at a trading company in Saudi Arabia. All amounts are in SAR.

Total purchases are 400 units for SAR 18,200. Total sales are 270 units for SAR 16,440, leaving 130 units in stock.

FIFO

• 15 Sep sale (150 units): the 100 oldest units at 40.00, then 50 at 46.00. Cost of sales: 4,000 + 2,300 = SAR 6,300.
• 28 Sep sale (120 units): 120 of the remaining 150 units at 46.00. Cost of sales: SAR 5,520.
• Closing stock (130 units): 30 at 46.00 plus 100 at 50.00 = SAR 6,380.

Moving weighted average

• After 10 Sep: 300 units costing 13,200, so the average is 44.00.
• 15 Sep sale: 150 × 44.00 = SAR 6,600. 150 units remain at 44.00 (6,600).
• After 22 Sep: 250 units costing 6,600 + 5,000 = 11,600, so the average is 46.40.
• 28 Sep sale: 120 × 46.40 = SAR 5,568.
• Closing stock: 130 × 46.40 = SAR 6,032.

Periodic weighted average

Averaging the whole month at once: 18,200 ÷ 400 units = 45.50. Cost of sales is 270 × 45.50 = SAR 12,285; closing stock is 130 × 45.50 = SAR 5,915.

The result side by side

Every method accounts for the same SAR 18,200. In a month of rising prices, FIFO reports SAR 348 more gross profit than the moving average, and carries exactly SAR 348 more in closing stock. Next month, when that stock is sold, the difference reverses.

What changes when prices fall?

When purchase prices fall, the picture flips. FIFO charges the older, higher costs to cost of sales first, so margins look thinner and closing stock carries the newer, lower prices. Weighted average still smooths the movement. Either way, check that stock isn’t carried above what you can sell it for: IAS 2 measures inventory at the lower of cost and net realisable value.

Which costing method suits a trading company?

There is no single right answer, but the questions below usually decide it.

If you distribute building materials, MEP products or industrial supplies, weighted average is often the natural fit: the units are interchangeable and buyers restock the same lines all year. FIFO earns its keep where the age of stock matters, or where finance wants the balance sheet close to current prices.

Whatever you choose, apply it consistently. IAS 2 requires the same cost formula for all inventories of a similar nature and use, and notes that a different location or tax regime alone doesn’t justify a different formula.

What about standard cost?

Standard cost is a third option: you set a fixed cost per item in advance, and every receipt and sale uses it. Whenever you buy at a different price, the difference goes to a purchase price variance account instead of changing the stock value.

Using the same month with a standard cost of SAR 45.00:

Cost of sales at standard is 270 × 45.00 = SAR 12,150; closing stock is 130 × 45.00 = SAR 5,850; and the SAR 200 adverse variance goes to profit or loss. Total cost charged this month: SAR 12,350, for a gross margin of 24.9%.

Standard cost makes margins predictable and shows buying performance at a glance. The trade-off is upkeep. IAS 2 allows the standard cost method for convenience only if the results approximate cost, and expects standards to be reviewed regularly and revised in the light of current conditions. In a trading business where prices move every month, that review is ongoing work.

What does IAS 2 say about costing methods?

IAS 2 Inventories sets the rules for companies reporting under IFRS Accounting Standards. According to the IFRS Foundation’s jurisdiction profiles, the UAE requires companies to apply international accounting standards, and Saudi Arabia requires IFRS as endorsed by SOCPA for listed companies and the IFRS for SMEs Accounting Standard for unlisted ones. The key points of IAS 2:

• Measurement (paragraph 9): inventories are measured at the lower of cost and net realisable value.
• Cost of purchase (paragraph 11): purchase price, import duties and other non-recoverable taxes, transport, handling and other directly attributable costs, less trade discounts and rebates.
• Standard cost (paragraph 21): allowed for convenience if the results approximate cost, with standards reviewed regularly.
• Specific identification (paragraph 23): required for items that are not ordinarily interchangeable.
• FIFO or weighted average (paragraph 25): for everything else, with the same formula for inventories of a similar nature and use.
• LIFO: not permitted.
• Disclosure (paragraph 36): the financial statements disclose the accounting policies used, including the cost formula.

Changing from one cost formula to another is a change in accounting policy under IAS 8, normally applied retrospectively. Agree it with your auditor and make the change at a period boundary. If you report under the IFRS for SMEs Accounting Standard, its inventory section takes the same line on FIFO, weighted average and LIFO; check the detail with your auditor.

How 1flux handles this

1flux sets the costing method per legal entity, so a company in one country and a subsidiary in another, in the same workspace, can each keep their own policy.