What is the Weighted Average Cost Method?
The weighted average cost method calculates inventory value by averaging purchase costs across all units on hand — here's how it works and why makers use it.
Last updated: March 2026
When you buy the same material at different prices over the course of a year — and you will — how do you figure out what it actually cost you to make each product? That’s the problem the weighted average cost method solves.
It’s one of three main inventory costing methods (alongside FIFO and LIFO), and it’s the one Craftybase uses by default. Once you understand how it works, the math starts to feel less like accounting jargon and more like common sense.
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What is weighted averaging?
Weighted averaging (or “rolling averaging”) calculates an average by factoring in both the value and the quantity of each item. It’s not just splitting the difference between two prices — it weights the average based on how many units were purchased at each cost.
You’ve probably encountered this before without realising it. In school, final exams count more toward your grade than a weekly quiz, even though both are “tests.” That’s weighted averaging. In inventory, the weighting factor is units on hand.
In perpetual inventory systems, this calculation runs every time there’s a stock change — a new purchase, a manufacture run, a sale. The result is a continuously updated average cost per unit, sometimes called a rolling or moving average.
How to calculate a weighted average
The formula is straightforward:
Weighted average cost formula
Sum of (Unit Cost × Quantity) ÷ Total Units = Weighted Average Unit Cost
Let’s work through a concrete example. Say you have a material you’ve purchased in two batches:
- 1 unit at $10
- 2 units at $20
Simple average: ($10 + $20) ÷ 2 = $15. But that ignores the fact that you bought more units at $20.
Weighted average: ($10 × 1 + $20 × 2) ÷ 3 = $50 ÷ 3 = $16.67
The extra weighting placed on the two $20 units pushes the average up. That’s a more accurate reflection of what your actual inventory costs.
How it works in a perpetual inventory system
The real power of weighted averaging shows up when you track stock changes over time. Every purchase or usage event recalculates the average. Here’s what that looks like in practice:
| Date | Transaction | Unit Cost | Qty Change | Stock on Hand Value | New Avg Unit Cost |
|---|---|---|---|---|---|
| 1 Jan | Purchase | $10.00 | +1 | $10.00 | $10.00 |
| 3 Jan | Purchase | $20.00 | +2 | $50.00 | $16.67 |
| 4 Jan | Used in production | — | -1 | $33.34 | $16.67 |
Notice that using stock doesn’t change the average cost — it just reduces the total quantity. The average only changes when you buy more stock at a different price.
This is the same calculation that runs inside Craftybase every time you add a purchase or record a manufacturing run. You don’t have to do this by hand.
Why is weighted average cost important for inventory?
For makers who buy the same material repeatedly at varying prices, a simple average would give you a distorted cost picture. Weighted averaging factors in price fluctuations as they happen, so your COGS figures stay accurate across the whole year.
A few specific benefits:
- More accurate cost per unit — accounts for actual purchase quantities at each price point, not just the price itself
- Smooths out price volatility — if your supplier raises prices mid-year, the average adjusts gradually rather than creating a sharp jump in your cost reports
- Consistent pricing across batches — products made from the same material have a consistent cost basis, which makes pricing decisions easier
- Simpler than FIFO — no need to track which specific units were used when; the rolling average handles it automatically
FIFO vs Weighted Average vs LIFO — what’s the difference?
There are three main inventory costing methods. Here’s how they compare:
| Feature | FIFO | Weighted Average | LIFO |
|---|---|---|---|
| How it assigns costs | Oldest stock used first | Average across all units on hand | Most recent stock used first |
| COGS when prices are rising | Lower (uses older, cheaper costs) | Middle — blended across all purchases | Higher (uses newest, pricier costs) |
| Inventory value when prices rise | Higher | Middle | Lower |
| Complexity | Medium — must track purchase layers | Lower — one rolling calculation | Higher — multiple cost layers |
| Allowed under IFRS? | Yes | Yes | No |
| Allowed under US GAAP? | Yes | Yes | Yes (US only) |
| Best for | Perishables with strict expiry tracking | Commodity materials with price variation | US tax strategies (specialty use) |
| Craftybase support | No | Yes (default) | No |
For most small handmade businesses, the weighted average method is the practical choice. FIFO requires tracking exactly which units were consumed in what order — fine for managing jam with an expiry date, but unnecessary overhead for soap base or candle wax. LIFO is mostly a US tax strategy and isn’t allowed in many countries.
The weighted average sits in the middle on every axis: middle complexity, middle COGS impact, middle inventory value. For makers dealing with fluctuating raw material costs and no need to track specific lot numbers, that “middle ground” is actually the sweet spot.
Why should your business use weighted average costing?
Beyond the accounting mechanics, there’s a practical case for weighted averaging that comes down to time and accuracy:
It’s less work. Once your inventory system is tracking purchases, the rolling average calculates itself. No manually assigning costs to specific batches.
It gives you reliable COGS figures. When you need to calculate cost of goods sold for tax time or pricing decisions, a weighted average gives you a defensible, consistent number.
It handles supplier price swings gracefully. Your costs don’t jump dramatically when prices shift — they blend in gradually as new stock is purchased.
It works for raw materials and finished goods. Whether you’re tracking ingredient costs or the fully manufactured products you sell, the same method applies.
How Craftybase handles weighted average costing
Craftybase is built around the weighted average cost method. Every time you record a material purchase or a manufacturing run, Craftybase recalculates the rolling average unit cost automatically — no spreadsheet formulas required.
This feeds directly into your COGS calculations. When an order comes in from Etsy, Shopify, or another connected channel, Craftybase uses the current weighted average cost of each component to calculate what that order actually cost you to fulfill. That figure flows into your COGS report and your Schedule C at year end.
The result: you always know what your products truly cost, not what you guessed they cost when you set a price three months ago.
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Frequently Asked Questions
What is the weighted average cost method?
The weighted average cost method is an inventory valuation approach that calculates the cost per unit by averaging all purchase prices, weighted by quantity. Instead of tracking exactly which units were used when, it maintains a rolling average that updates each time new stock is purchased. This gives you a consistent, blended cost figure across all your inventory — especially useful when material prices fluctuate throughout the year.
How do I calculate the weighted average cost of inventory?
Multiply each purchase quantity by its unit cost, add those figures together, then divide by total units on hand. For example: 1 unit at $10 and 2 units at $20 gives (1×$10 + 2×$20) ÷ 3 = $16.67. In a perpetual inventory system, this recalculates automatically every time you record a new purchase. Craftybase handles this calculation in real time — you just enter your purchases and it keeps the running average current.
What's the difference between FIFO, LIFO, and weighted average cost?
FIFO (First In, First Out) assigns costs using the oldest purchase prices first. LIFO (Last In, First Out) uses the most recent prices first — it's banned under IFRS and mainly used for US tax purposes. Weighted average cost blends all purchase prices proportionally by quantity, landing between FIFO and LIFO in terms of reported COGS and inventory value. For most makers, weighted average is the lowest-friction option because it doesn't require tracking individual purchase lots.
Which inventory costing method is best for small handmade businesses?
Weighted average cost is the best fit for most small handmade businesses. It's simpler than FIFO (no need to track which specific batches were consumed) and more practical than LIFO (which is prohibited outside the US). If you buy the same materials repeatedly at varying prices — which most soap, candle, and jewelry makers do — the rolling average gives you a stable, reliable cost basis without extra record-keeping overhead.
Does Craftybase use the weighted average cost method?
Yes. Craftybase uses weighted average costing by default for all material and product inventory. Every time you record a purchase, manufacture, or sale, the rolling average unit cost updates automatically. This feeds directly into your COGS calculations and year-end financial reports — so you always have an accurate, up-to-date picture of what your products truly cost to make, without manual spreadsheet work.
Does the weighted average cost method work for perpetual inventory?
Yes — weighted average cost is specifically well-suited to perpetual inventory systems, where stock levels update in real time. In a perpetual system, the weighted average recalculates every time a purchase is recorded, giving you a continuously accurate cost figure. This is sometimes called a "moving average" or "rolling average." Periodic inventory systems can also use weighted average, but the calculation only happens at set intervals rather than continuously.
