Inventory valuation assigns a cost to units sold and units still on hand. That cost affects cost of goods sold, gross profit, the inventory asset on the balance sheet, and, depending on the jurisdiction, taxable income.
The core relationship is:
cost of goods sold = beginning inventory + net purchases and production cost - ending inventoryThe physical movement of goods and the accounting cost formula are related but not always identical. A warehouse may rotate perishable goods physically by first expiry while its accounting policy uses a permitted cost formula consistently.
The five methods at a glance
| Method | How cost is assigned | Common fit | Important caution |
|---|---|---|---|
| FIFO | Oldest costs move to COGS first | Interchangeable goods and many general inventories | Ending inventory reflects newer costs |
| LIFO | Newest costs move to COGS first | Permitted U.S. tax and reporting situations | Not permitted under IFRS |
| Weighted average | One average unit cost is applied | High-volume, interchangeable units | Smooths price changes |
| Specific identification | Actual cost follows the identified item | Unique, serialized, or high-value items | Requires reliable item-level traceability |
| Retail method | Cost is estimated from retail value and cost-to-retail ratios | Retail interim estimates and large assortments | An estimate, not a substitute for sound records |
The applicable accounting and tax rules depend on the entity and jurisdiction. IAS 2 permits specific identification for non-interchangeable items and FIFO or weighted average for ordinarily interchangeable items. In the United States, IRS Publication 538 discusses specific identification, FIFO, LIFO, and retail inventory rules. Ask a qualified accountant before selecting or changing a reporting method.
A common example
Assume a business buys 200 units at $30 and later buys 300 units at $40. Total inventory available is 500 units costing $18,000. The business sells 150 units.
1. First in, first out (FIFO)
FIFO assigns the oldest costs to the units sold first.
COGS = 150 x $30 = $4,500
ending inventory = 50 x $30 + 300 x $40 = $13,500When purchase costs rise, FIFO usually reports lower COGS and higher ending inventory than LIFO for the same transactions.
2. Last in, first out (LIFO)
LIFO assigns the newest costs to the units sold first.
COGS = 150 x $40 = $6,000
ending inventory = 150 x $40 + 200 x $30 = $12,000LIFO rules can be complex. It is available in some U.S. circumstances but is not an IAS 2 cost formula, so businesses reporting under IFRS should not use it.
3. Weighted average cost
Weighted average combines the cost of interchangeable units into one average.
average unit cost = $18,000 / 500 = $36
COGS = 150 x $36 = $5,400
ending inventory = 350 x $36 = $12,600A periodic system calculates the average for a reporting period. A perpetual moving-average system recalculates after each purchase, so the result can differ when sales occur between receipts.
4. Specific identification
Specific identification assigns the actual cost of an identified item to COGS when that item is sold. It works for unique or traceable units such as vehicles, artwork, custom machinery, or serialized equipment.
Suppose four identified items cost $110, $200, $500, and $650. If the $500 item sells, COGS is $500 and ending inventory is $960. The calculation is direct, but only if the system reliably connects the physical unit, its acquisition cost, and the sale.
5. Retail inventory method
The retail method estimates ending inventory at cost from the retail value of goods and a cost-to-retail ratio. A simplified form is:
goods available at retail - sales at retail = ending inventory at retail
ending inventory at retail x cost-to-retail ratio = estimated ending inventory at costAssume goods available have a $100,000 retail value and $60,000 cost, giving a 60% cost-to-retail ratio. If sales at retail are $70,000, ending inventory at retail is $30,000 and its estimated cost is $18,000.
Markup, markdown, department, and LIFO treatments can change the calculation. Apply the rules required by the relevant accounting and tax framework.
How to choose an inventory valuation method
Consider five questions:
- Are units interchangeable? Unique items favor specific identification; interchangeable units fit a cost formula.
- Which framework applies? Tax, U.S. GAAP, IFRS, and local statutory reporting may permit different treatments.
- Can the system support it? Item-level identification and moving averages require accurate transaction data.
- Does it reflect the operation consistently? A method should produce reliable, repeatable reporting rather than a desired one-period result.
- What happens when costs change? Run a sensitivity comparison so managers understand the effects on COGS, margin, and ending inventory.
Changing an accounting method can require approval, disclosures, or tax filings. Consistency is important because switching methods can make periods difficult to compare.
Controls that protect inventory valuation
- reconcile the inventory subledger to the general ledger;
- perform physical counts or cycle counts and investigate differences;
- separate owned goods from consigned or customer-owned goods;
- capture freight and other permitted landed costs consistently;
- review slow-moving, damaged, and obsolete stock for write-down;
- test negative quantities, unusual unit costs, and backdated transactions;
- lock the reporting period after review and document adjustments.
Strong inventory control protects the quantities underneath the calculation. A precise cost formula applied to an inaccurate count still produces an inaccurate inventory value.