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Weighted Average Inventory Calculator
Enter your beginning inventory, then each purchase and sale in order. The weighted average cost per unit, the cost of goods sold, and the ending inventory update as you type — under either periodic or perpetual costing.
Method
Beginning inventory
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What Is the Weighted Average Inventory Method?
The weighted average inventory method values every unit at the same average cost, calculated from all units available for sale, instead of tracking which specific unit was sold.
Stock bought at different prices is pooled. Beginning inventory and every purchase are added together in both units and cost, and one average cost per unit falls out of that pool. Each unit sold and each unit left over carries that same figure.
It is also called the average cost method, or AVCO. Both IFRS and US GAAP permit it, which is one reason it appears so widely in businesses holding identical, interchangeable goods — fuel, grain, screws, chemicals, components.
The appeal is that no unit needs a history. FIFO and LIFO both require you to know which layer a sale came from. Weighted average asks only what everything cost in total and how many units there were. That same total-divided-by-total idea is the weighted average calculator in its simplest form.
How to Calculate Weighted Average Inventory
To calculate weighted average inventory, divide the total cost of goods available for sale by the total units available, then apply that cost to units sold and units remaining.
Weighted Average Inventory Formula
Avg cost = Cost of goods available for sale Units available for sale
The two outputs always reconcile: COGS plus ending inventory equals the cost of goods available for sale. If they do not add up, a figure has been entered twice or missed.
Step-by-Step Weighted Average Inventory Calculation
- Start with beginning inventory. Record the units on hand and their cost per unit.
- Add every purchase in the period. Units and cost, at the price actually paid.
- Total the units available for sale. Beginning units plus purchased units.
- Total the cost of goods available for sale. Beginning cost plus purchase costs.
- Divide cost by units. This is the weighted average cost per unit.
- Apply it twice. Units sold × average cost is COGS; units left × average cost is ending inventory.
Weighted Average Inventory Calculation Example
A business opens the period with 100 units at $10 and makes two purchases, then sells 300 units.
| Source | Units | Unit cost | Total cost |
|---|---|---|---|
| Beginning inventory | 100 | $10.00 | $1,000.00 |
| Purchase 1 | 200 | $12.00 | $2,400.00 |
| Purchase 2 | 150 | $14.00 | $2,100.00 |
| Available for sale | 450 | $12.22 | $5,500.00 |
$5,500 ÷ 450 units = $12.2222 per unit
Selling 300 units gives a COGS of $3,666.67 and leaves 150 units worth $1,833.33. Those two add back to the $5,500 of goods available, which is the check to run on every calculation.
How to Use the Weighted Average Inventory Calculator
Fill in beginning inventory, list purchases and sales in date order, and the average cost, COGS and ending inventory appear immediately.
Enter Beginning Inventory
Put the units carried into the period and their cost per unit in the beginning inventory box above the transaction list. Leave it empty for a business starting with no stock — the calculation still works from the first purchase.
Add Purchases and Costs
Add one row per purchase, set the type to Purchase, and enter the units and the cost per unit actually paid. Freight and duty belong in that cost if your policy capitalises them.
- Description names the row — March purchase, PO 4471. Optional, and it appears in the breakdown.
- Add transaction creates another row, and the Enter key on the last row does the same.
- Currency sets the symbol used for every amount on the panel.
- Decimals controls the displayed precision of the average cost, up to 4 places.
Enter Units Sold
Set a row's type to Sale and enter the units. The unit cost field switches off, because a sale takes stock out at the average cost the calculator already holds rather than at a price you supply.
Order matters under perpetual costing, so list transactions by date. Under periodic costing the order is irrelevant, since one average covers the whole period.
Calculate Ending Inventory and Cost of Goods Sold
No button is needed. Beside the average cost, the panel reports 4 figures:
- Cost of goods sold — the cost released to the income statement.
- Ending inventory value — the cost still sitting on the balance sheet.
- Ending inventory units — what remains on hand.
- Goods available — the units and cost the whole calculation divides.
The bar underneath shows how the cost of goods available splits between COGS and closing stock, and the right-hand column of each row shows the running average after that transaction when perpetual costing is selected.
Periodic vs. Perpetual Weighted Average Inventory
Periodic costing calculates one average at the end of the period. Perpetual costing recalculates a moving average after every purchase, so the two produce different figures from identical transactions.
Periodic Weighted Average Method
Everything is pooled first and costed afterwards. The average of $12.2222 covers all 450 units, whenever they arrived, and every one of the 300 units sold is charged at that rate. COGS is $3,666.67 and ending inventory is $1,833.33.
It is the simpler method and needs only period totals, which suits a business that counts stock at period end rather than tracking it continuously.
Perpetual Weighted Average Method
The average is recomputed the moment new stock arrives, and each sale is costed at whatever the average is on that date. With the same transactions ordered March and April, the running average moves twice.
| Transaction | Units on hand | Cost on hand | Average cost |
|---|---|---|---|
| Beginning inventory | 100 | $1,000.00 | $10.0000 |
| Purchase 200 @ $12 | 300 | $3,400.00 | $11.3333 |
| Sell 180 | 120 | $1,360.00 | $11.3333 |
| Purchase 150 @ $14 | 270 | $3,460.00 | $12.8148 |
| Sell 120 | 150 | $1,922.22 | $12.8148 |
COGS becomes $3,577.78 and ending inventory $1,922.22 — still adding to $5,500, but $88.89 of cost has moved from the income statement to the balance sheet. The first 180 units were sold before the more expensive April stock arrived, and perpetual costing records that.
Weighted Average Cost of Inventory
The weighted average cost is the single per-unit figure every unit carries, and it is the number both COGS and ending inventory are built from.
Weighted Average Cost Formula
average cost = (beginning cost + purchases) ÷ (beginning units + units purchased)
The formula is a weighted average in the ordinary sense: each purchase price is weighted by the number of units bought at it. A price paid on 200 units counts twice as heavily as the same price paid on 100. For single-item purchase costing without the COGS and ending-inventory split, use the weighted average cost calculator.
Weighted Average Cost Example
| Source | Unit cost | Share of units | Contribution to average |
|---|---|---|---|
| Beginning inventory | $10.00 | 22.2% | $2.2222 |
| Purchase 1 | $12.00 | 44.4% | $5.3333 |
| Purchase 2 | $14.00 | 33.3% | $4.6667 |
| Weighted average cost | — | 100% | $12.2222 |
The simple average of $10, $12 and $14 is $12.00. The weighted average is $12.2222, higher because the two dearer batches make up 78% of the units. On 450 units that 22 cent gap is $100 of inventory value.
How Weighted Average Affects COGS and Ending Inventory
Weighted average smooths cost changes, placing COGS and ending inventory between what FIFO and LIFO would report.
Every unit carries the same cost, so a price spike is spread across all stock rather than landing on the units sold immediately after it. Reported margins move less from month to month, which is the method's main attraction.
| Method | COGS on 300 units | Ending inventory | Effect on profit |
|---|---|---|---|
| FIFO | $3,400.00 | $2,100.00 | Highest profit |
| Weighted average | $3,666.67 | $1,833.33 | Between the two |
| LIFO | $3,900.00 | $1,600.00 | Lowest profit |
The $500 spread in COGS between FIFO and LIFO is real profit, and weighted average lands in the middle of it. Because costs were rising here, weighted average reports less profit than FIFO and more than LIFO. With falling costs the order reverses.
One consequence is worth planning for: whichever method you pick, COGS and ending inventory always sum to the same $5,500. Choosing a method decides how that fixed pool is split between the income statement and the balance sheet, not how large it is.
Weighted Average vs. FIFO and LIFO
FIFO sells the oldest units first, LIFO the newest, and weighted average refuses to distinguish them at all.
Weighted Average vs. FIFO
FIFO charges the earliest costs to COGS and leaves the newest costs in inventory. When prices rise, that means low COGS, high profit, and an ending inventory close to current replacement cost — $3,400 and $2,100 in the example against $3,666.67 and $1,833.33 under weighted average.
FIFO tracks cost layers, so it needs records of what each batch cost and how much of it remains. Weighted average needs only totals, which is why it is far easier to run on interchangeable goods.
Weighted Average vs. LIFO
LIFO charges the newest costs to COGS, giving the highest COGS and lowest profit while prices rise — $3,900 against $3,666.67 here. Its ending inventory of $1,600 sits on old costs that can drift far from today's prices.
LIFO is also restricted: IFRS prohibits it outright, and US GAAP requires the same method in financial statements as in tax filings when it is used. Weighted average is accepted under both frameworks, which makes it the practical choice for businesses reporting internationally.
Advantages and Limitations of the Weighted Average Method
It is the simplest method to run and the hardest to manipulate, at the cost of never reflecting any single unit's actual cost.
Advantages of Weighted Average Inventory
- Simple to operate. Two totals produce the cost, with no layers to track.
- Smooths price volatility. A spike is spread across all units rather than distorting one month.
- Hard to game. Timing a purchase near period end barely moves the average, while it can shift LIFO sharply.
- Accepted everywhere. Permitted under both IFRS and US GAAP.
- Fits interchangeable goods. When units are identical, tracking which one sold adds cost and no information.
Limitations of Weighted Average Inventory
- No unit matches its real cost. Every unit is valued at a figure that may equal no invoice you hold.
- Ending inventory lags the market. Old low costs stay in the average long after prices move.
- Recalculation burden under perpetual costing. Every purchase changes the average, which is impractical by hand.
- Wrong for unique items. Serialised or high-value goods need specific identification, not an average.
- Two answers from one dataset. Periodic and perpetual disagree, so the policy must be stated and applied consistently.
Common Weighted Average Inventory Calculation Mistakes
Six mistakes account for most weighted average figures that fail to reconcile.
- Averaging the unit prices. $10, $12 and $14 average to $12.00, not the correct $12.2222. Prices must be weighted by units bought.
- Leaving beginning inventory out. Opening stock is part of goods available for sale and belongs in both totals.
- Recalculating after a sale. A sale removes units and cost at the current average and never changes the average itself.
- Mixing the two methods. A periodic average applied to perpetual records produces a figure that reconciles to neither.
- Forgetting freight and duty. If policy capitalises them, they belong in the purchase cost before averaging.
- Rounding the average too early. Rounding $12.2222 to $12.22 before multiplying by 450 units loses a dollar of inventory.
The reconciliation check catches almost all of these: COGS plus ending inventory must equal the cost of goods available for sale. The calculator prints all three, so a broken total is visible at a glance.
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Frequently Asked Questions
How Do You Calculate Weighted Average Inventory?
Divide the cost of goods available for sale by the units available for sale, then multiply that average by the units sold for COGS and by the units remaining for ending inventory. $5,500 across 450 units gives $12.2222 per unit.
What Is the Weighted Average Inventory Formula?
Average cost = (beginning inventory cost + purchases) ÷ (beginning units + units purchased). COGS is units sold × average cost, and ending inventory is units remaining × average cost.
What Is the Difference Between Periodic and Perpetual Weighted Average?
Periodic calculates one average at period end and applies it to every sale. Perpetual recalculates a moving average after each purchase and costs each sale at the average on that date. The same transactions gave $3,666.67 and $3,577.78 of COGS.
How Does Weighted Average Affect COGS?
It smooths COGS, placing it between FIFO and LIFO. With rising prices in the example, COGS was $3,400 under FIFO, $3,666.67 under weighted average, and $3,900 under LIFO.
How Does Weighted Average Affect Ending Inventory?
Ending inventory is valued at the same average as COGS, so it sits between FIFO and LIFO too — $1,833.33 here, against $2,100 under FIFO and $1,600 under LIFO. COGS and ending inventory always sum to goods available for sale.
What Is the Difference Between Weighted Average and FIFO?
FIFO charges the oldest costs to COGS and leaves the newest in inventory, so rising prices produce higher profit than weighted average. FIFO also requires cost layers to be tracked, while weighted average needs only totals.
What Is the Difference Between Weighted Average and LIFO?
LIFO charges the newest costs to COGS, giving higher COGS and lower profit than weighted average while prices rise. LIFO is also banned under IFRS, whereas weighted average is accepted under both IFRS and US GAAP.
When Should a Business Use the Weighted Average Inventory Method?
Use it when units are interchangeable and tracking individual costs adds no information — fuel, grain, fasteners, chemicals, components. It also suits businesses wanting steadier reported margins through volatile purchase prices.
What Is Weighted Average Cost?
Weighted average cost is the per-unit figure every unit carries: total cost of goods available divided by total units available. It weights each purchase price by the number of units bought at that price, which is why it differs from a simple average of prices.
Can Weighted Average Inventory Be Used for Multiple Purchases?
Yes, that is the normal case. Add a row per purchase and the calculator pools them all. Under perpetual costing each purchase resets the running average, which the right-hand column of each row displays.
Calculate Weighted Average Online
Every value-weight pair, one weighted average.
The weighted average calculator multiplies each value by its weight, adds the weighted sum, divides by the total of weights, and prints the weighted average beside the standard arithmetic mean. Course grades, GPA, portfolio returns, and probability distributions all run through the same 4 steps.
Open the Weighted Average Calculator