FIFO vs weighted average inventory: which method should your small business use?

If you buy and sell physical goods, your accounting has a question that sounds boring but quietly shapes your profit: when you sell one item out of stock that you bought at different prices, which cost do you record?

FIFO vs weighted average inventory are the two most common answers, and choosing one affects your reported profit, your tax bill, and how your balance sheet looks to a lender. Here's what each method does, in plain language.

FIFO vs weighted average inventory: the core idea

Both methods answer the same question — the cost of goods sold (COGS) — by making an assumption about the order stock flows out.

Under FIFO (first in, first out), you assume the oldest items sell first. The cost recorded for each sale comes from the earliest purchases still in stock. What's left on the shelf is valued at the most recent purchase prices.

Under the weighted average method, you blend every purchase price into one average cost per unit. Each sale is recorded at that average, and remaining stock is valued at it too. (Technically there are two flavors: a periodic average computed once per period, and a moving average recalculated after every purchase — the moving average is what most small-business systems use.)

A worked example: FIFO vs weighted average inventory in numbers

Say you run a small trading business. During the quarter:

1 January: buy 100 units at $10 each → $1,000
1 March: buy 100 units at $12 each → $1,200
Total available: 200 units, $2,200

You sell 120 units at $20 each → revenue $2,400.

FIFO: the 120 sold units cost 100 × $10 + 20 × $12 = $1,240. Ending inventory: 80 × $12 = $960. Gross profit: $2,400 − $1,240 = $1,160.

Weighted average: average cost = $2,200 ÷ 200 = $11.00 per unit. COGS = 120 × $11 = $1,320. Ending inventory: 80 × $11 = $880. Gross profit: $2,400 − $1,320 = $1,080.

Same business, same quarter, same sales — different profit. That's why the choice matters.

When prices rise: FIFO shows higher profit and higher tax

Notice the pattern in the example: because purchase prices were rising, FIFO recorded the cheaper old costs against sales, producing $80 more profit than weighted average.

In a rising-price environment — the normal state of most economies — FIFO generally reports higher gross profit and higher ending inventory values than weighted average, because the balance sheet reflects the most recent (higher) costs. Higher reported profit usually means a higher tax bill. When prices fall, the effect reverses: FIFO shows lower profit.

Weighted average smooths everything out. It sits between FIFO and (in rising markets) lower profit figures, because the blended cost reacts to price changes gradually rather than in steps.

Which one should you pick?

There is no universally right answer, but there are good heuristics:

Perishables and time-sensitive goods (food, pharmaceuticals, fashion): FIFO matches physical reality — you genuinely sell the oldest stock first. Auditors and lenders understand it intuitively.
Commodities and interchangeable goods (hardware, chemicals, raw materials) where units are identical and mixed together: weighted average is the honest reflection of how stock actually flows.
Tax planning: in a rising-price environment, weighted average reports slightly lower profit, which can reduce tax — but only if your tax rules permit it. Always confirm with your accountant.
Simplicity: weighted average (moving average) is easier for a small team to operate day to day, because every item of a product shares one current cost.

One hard rule: whatever you pick, apply it consistently from period to period. Switching methods year to year to flatter the numbers is not allowed under IAS 2 (the standard requires the same cost formula for all inventories of a similar nature and use), and your tax authority will ask questions.

What IAS 2 allows (and bans)

The accounting standard for inventories, IAS 2, permits FIFO and the weighted average cost formula. It explicitly bans LIFO (last in, first out) — you cannot assume the newest items sell first, even though some tax regimes historically allowed it. If your software offers LIFO, do not use it for IFRS financial statements.

Practical tips for a small business

Pick one method per inventory group (all finished goods of similar nature use the same formula).
Write it down in your accounting policy note — a lender or auditor will ask.
Let your software do the math. A modern invoicing or inventory system should recalculate moving averages automatically on every purchase. Spreadsheets work at tiny scale; past a few hundred lines, they become an error factory.
Count stock regularly. Both methods assume the quantities are right. A method can't fix missing units.

Getting inventory valuation right is one of the quiet foundations of trustworthy financial statements — and it's exactly the kind of routine we're building into Point, so a small team can keep clean stock records without an accounting degree.

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