What is average weighted cost?
Average weighted cost exists to smooth out price swings, so that cost of goods sold (COGS) and inventory value stay consistent even when purchase prices change from one order to the next. The method shows up most often in manufacturing and retail operations that move large volumes of identical or interchangeable goods, where tracking each unit separately would be impractical. According to IHL Group’s 2026 Inventory Distortion Study, inventory distortion reached $1.7 trillion in global retail, equal to 6.2% of global retail sales — a reminder of why accurate inventory costing matters.
Key characteristics
- One blended cost: WAC merges every unit into a single cost per unit, so there is no per-item tracking to maintain.
- Simple formula: WAC = total cost of goods available for sale / total units available for sale.
- Best fit: identical or interchangeable goods, frequent purchases, and fluctuating prices. See how it compares with other common costing methods.
- Standards-accepted: The WAC method is permitted under both GAAP and IFRS accounting. Under IFRS, IAS 2 names weighted average cost as one of two cost formulas alongside FIFO.
- Periodic vs. perpetual: periodic recalculates the average at period end, while perpetual (moving average) recalculates after each purchase. In Fishbowl, the average recalculates only when new units are received, not when units sell, and it resets when stock reaches zero. That is built-in discipline that keeps your costing honest.
Example
Picture a bolt and fastener supplier that starts a period with 100 units valued at $1,000 in total. During the period, the supplier buys 200 more units for $3,000, which brings the running total to $4,000 across 300 units. Divide $4,000 by 300, and the average cost lands at $13.33 per unit. The business then applies that $13.33 figure to value remaining stock, calculate cost of goods sold, and report ending inventory.
Related terms
FAQ
Is weighted average cost the same as average cost?
Yes. “Average weighted cost,” “weighted average cost,” and the “average-cost method” all describe the same blended-cost approach to valuing inventory.
When should a business use WAC?
A business should reach for WAC when its goods are identical or interchangeable, when prices fluctuate, or when tracking each individual unit’s cost is impractical.
Is WAC allowed under GAAP and IFRS?
Both accept it. Under IFRS’s IAS 2, weighted average cost is one of two named cost formulas alongside FIFO.
Fishbowl keeps that blended cost accurate for you, recalculating on receipt and resetting at zero, so your books and your shelves agree.