FIFO vs Weighted Average Cost: Which Inventory Valuation Method Should You Use?

FIFO and weighted average are two ways to turn receipt costs into a cost for the units you sell and a value for the units you still hold. FIFO uses the oldest receipt cost first. Weighted average blends the costs you have on hand into one unit cost.

You pick one method as the valuation policy for the business. A report can still show the other calculation so you can compare them. That comparison is a view. It is not a second set of books.

What FIFO does with receipt layers

FIFO means first in, first out. Each receipt keeps its own unit cost, as a layer, until those units are sold or otherwise leave inventory.

When you sell, you consume the oldest layer first. If that layer is smaller than the sale, you finish it and take the rest from the next oldest layer. Units that remain keep the cost of the layers that have not been consumed yet.

FIFO is useful when purchase costs move and you want the cost of goods sold to reflect the earlier buy, and the remaining stock to reflect the later buy. It is also the method people usually mean when they talk about "layers" after two shipments arrive at two different landed costs.

What weighted average does

Weighted average, often shortened to WAC, adds up the cost of the units on hand and divides by the number of units. Every unit then carries that one blended cost until the next receipt changes the blend.

A new receipt at a higher cost pulls the average up. A new receipt at a lower cost pulls it down. The sale does not pick an old layer and a new layer. It multiplies the quantity sold by the current average.

WAC is useful when units are interchangeable and a single current cost is easier to explain than a stack of historical shipments. It hides the difference between those shipments on purpose. That is the method, not a missing report.

One hypothetical shipment, two answers

This example is hypothetical. It is not a customer record, and it ignores tax, discounts, and later returns so the arithmetic stays visible.

You receive two lots of the same item, then sell 12 units. Both receipt costs below are landed costs: invoice price plus the freight or duty already allocated to that receipt. How that allocation is done is covered in the landed cost guide.

• Receipt A: 10 units at $40 landed cost. Extended cost $400.
• Receipt B: 10 units at $52 landed cost. Extended cost $520.
• Total before the sale: 20 units, $920.

FIFO for the sale of 12

The oldest layer is Receipt A. All 10 of those units go out at $40, which is $400. The sale still needs 2 units, so those come from Receipt B at $52, which is $104.

• Cost of the 12 units: $400 + $104 = $504.
• Units left: 8, all from Receipt B.
• Value of what remains: 8 × $52 = $416.
• Check: $504 + $416 = $920, the cost that came in.

Weighted average for the same sale

Average unit cost before the sale: $920 / 20 = $46.

• Cost of the 12 units: 12 × $46 = $552.
• Units left: 8.
• Value of what remains: 8 × $46 = $368.
• Check: $552 + $368 = $920.

The total cost that entered inventory is the same. The split between "sold" and "still here" is not. In this example FIFO charges the sale less, because it uses the cheaper layer first, and it leaves the dearer layer in stock. Weighted average charges the sale more and leaves a lower remaining value. A later sale, or a receipt in the other price order, can reverse that pattern. Do not treat this one case as proof that FIFO always produces a lower cost of goods.

Where landed cost changes the unit cost

If Receipt B's invoice price was $40 and freight allocated on that receipt added $12, the landed cost is $52. FIFO then has a $52 layer. Weighted average uses $52, not $40, when it blends.

That is why the receipt matters more than the purchase order for valuation. The order can show the supplier's price. The receipt is where extra cost pools are allocated onto the units that arrived. Two receipts of the same item, with two different freight bills, are two costs. FIFO keeps them as layers. Weighted average folds the second receipt into the average as soon as it is received.

A confirmed purchase order that has not been received yet has no layer and does not change the average. Stock and cost both wait for the goods receipt.

One stored policy, and a report that can show the other

Inveta stores one valuation policy for the account: FIFO or weighted average. Weighted average is the default until you change it. Movements that need a unit cost, including a transfer between locations, use that stored policy.

Cost analysis can also be calculated under the other method. That is a way to see what the same receipts would look like if you had used the other rule. It does not mean the business is keeping two official valuations at once. If the stored policy is weighted average, the operational cost is the average. A FIFO view on a report is a comparison, not a second ledger, and it does not rewrite the history of costs already recorded under the stored policy.

Switching the stored policy later is a decision about which rule to use going forward. This article does not claim that a switch reconstructs every past sale. Do not assume closed history silently converts from layers into an average, or the other way around, without checking the records you already posted.

Which method fits the operation

Use FIFO when shipments of the same item regularly arrive at different landed costs and you want remaining stock to carry the newer cost. Distributors who buy the same SKU from a supplier whose freight changes by season often care about that split. The layers are only as good as the receipt costs. A missing freight pool makes a clean FIFO layer that is still the wrong number.

Use weighted average when units are interchangeable and people need one current cost: a reorder check, a branch transfer, a price review. The average moves with each receipt. It will not tell you that the units still on hand "came from" the expensive container. If that sentence matters, FIFO is the clearer policy.

Spare-parts businesses often use average for bins of identical consumables and still care about FIFO for items whose replacement cost jumps. The valuation policy in Inveta is one setting for the account, not a different method per item. Pick the method that should apply to the stock you actually cost, and keep receipt costs complete enough for that method to mean something.

Neither method is a certification. Inveta does not claim GAAP or IFRS compliance, and it does not file tax returns from a valuation toggle. The numbers above are arithmetic on two hypothetical receipts. Your accountant still decides what your financial statements require.

What changes the result, and what does not

The result changes when:

• A new receipt arrives at a different landed cost.
• You sell or issue a quantity that crosses from one FIFO layer into the next.
• A cost pool on a receipt changes the landed cost before you treat that cost as final.

The result does not change when:

• You only confirm a purchase order.
• You look at the other method in a cost analysis view, if you leave the stored policy alone.
• You transfer a unit and expect the transfer to invent a new purchase cost. A transfer moves quantity. Its unit cost follows the policy already stored. It is not a new supplier receipt.

Serial and batch identity are also separate from this choice. A serial tells you which unit moved. A batch tells you which lot and quantity moved. FIFO and weighted average tell you what cost to attach. You can track a lot and still cost it with either policy. The serial and batch article covers identity. This one covers cost.

Frequently asked questions

Can I keep FIFO and weighted average as two official valuations?

No. One policy is stored for the account. Cost analysis can show the other calculation as a view. Use the stored policy as the cost you operate with.

Does the cheaper receipt always get sold first under FIFO?

Only if it is the older layer. FIFO follows receipt order, not "whichever cost is lower." In the example, Receipt A was both older and cheaper. If the $52 receipt had arrived first, FIFO would have sold that layer first.

Why is my average not the invoice price?

Because the average uses landed cost after receipt charges are allocated, and because it blends every unit still on hand. Freight on one receipt changes the blend even when the supplier invoice did not.

Does a transfer create a new FIFO layer at a new price?

A transfer is not a new purchase. It moves stock and uses the stored valuation policy for the unit cost of that move. A new layer at a new purchase cost comes from a new receipt, not from sending goods to another warehouse.

Will this article's $504 and $552 appear in my account?

No. Those figures exist only for the hypothetical 10 at $40, 10 at $52, and a sale of 12. Your receipts, quantities, and allocated freight will produce different numbers. The check that still applies is the same: cost sold plus cost remaining should equal the cost that came in, for the units in the example you are reviewing.

Use one rule, and feed it real receipt costs

FIFO leaves a trail of layers. Weighted average keeps one moving unit cost. Both can be right for a business, and both are wrong if the receipt cost is only the supplier invoice while the freight sat in a spreadsheet.

Choose the policy before the second shipment arrives, and put landed cost on the receipt that created the layer or the new average. The inventory costing tools are there for that sequence. When you want the policy on your own items, create an Inveta account and receive two shipments before you judge the method on a single invoice price.