Inventory valuation methods: average, FIFO and LIFO

How much did what you sold this month cost? If the purchase price of your merchandise never changed, the answer would be immediate. In the real world, though, prices move, purchases arrive in different batches, and two units of the same product can have different costs depending on when they were bought. When it is time to calculate the cost of sales and the value of the inventory still in your warehouse, you need a clear rule that tells you which cost to assign to each unit that goes out. That rule is the inventory valuation method, and choosing it well is one of the accounting decisions with the biggest impact on your results. In this article we explain what inventory valuation is, what it is used for, which are the three most common methods (weighted average, FIFO and LIFO), how each one works with a short numerical example, how they compare against each other and how to choose the right one for your business. You will also see the direct relationship between the method you choose and the inventory card or kardex, because the method is not a theoretical concept: it is what defines the numbers recorded on every issue from your stock record. If you only want the short answer: inventory valuation assigns a cost to the units sold and to the ending inventory, and the three main methods differ in the order in which they assume purchase costs flow out.

What inventory valuation is and why it matters

Inventory valuation is the accounting procedure that assigns a cost to two things: the units that leave the warehouse during the period (through sales, consumption or shrinkage) and the units that remain as ending inventory. The cost assigned to the units that leave becomes the cost of sales, the figure subtracted from revenue to calculate gross profit; the cost assigned to the remaining units is reported as an asset on the balance sheet and becomes the opening inventory of the next period. It is hard to overstate its importance: changing the method or making a calculation error changes the reported profit, the tax to be paid and the value of the asset, even when the physical merchandise is exactly the same. That is why accounting standards demand consistency: once a method is chosen, it must be applied in the same way period after period, unless there is a valid justification and proper disclosure for changing it. To understand the methods, remember the basic cost of sales formula: opening inventory, plus purchases for the period, minus ending inventory. The total cost available is the same no matter which method you use; what changes is how that cost is split between cost of sales and ending inventory. That split depends on the cost flow assumption behind each method: whether costs flow out in the same order they came in, in reverse order, or all mixed together into a single average cost.

Weighted average cost method

The weighted average calculates a single unit cost for all the available inventory by dividing the total cost by the total number of units available: average cost = total cost available ÷ total units available With that average unit cost you value both the units sold and the ending inventory, without distinguishing which purchase each unit came from. It is one of the most widely used methods in practice because it smooths out price fluctuations: neither expensive nor cheap purchases hit the period's result all at once. It is also simple to run, because you only need to manage one unit cost at a time, and it is accepted by international financial reporting standards. Short numerical example: suppose you have 100 units at $10, buy 200 units at $12 and then 200 units at $15. The total cost available is 100 × $10 + 200 × $12 + 200 × $15 = $1000 + $2400 + $3000 = $6400, for 500 units available. The average cost is $6400 ÷ 500 = $12.80 per unit. If you sell 300 units, the cost of sales is 300 × $12.80 = $3840 and the ending inventory of 200 units is valued at 200 × $12.80 = $2560. Note that $3840 + $2560 = $6400: the available cost was fully allocated.

FIFO method (first in, first out)

FIFO, known in Spanish as PEPS (primeras entradas, primeras salidas), assumes that the first units that entered the warehouse are the first ones to leave. Under this assumption, each issue is deducted from the oldest batches available and the ending inventory is made up of the most recent purchases. Physically it does not have to be that way in the warehouse: FIFO is a cost flow assumption, not a rule about how boxes actually move. In a context of rising prices, FIFO produces the lowest cost of sales of the three methods, because issues are valued at the older, cheaper costs, and consequently gross profit is the highest. Ending inventory, on the other hand, is valued at recent costs, close to the current market price, which gives a realistic picture of replacement value. FIFO is accepted under international standards (IFRS) and is especially logical for perishable goods or items with expiration dates, where physically you do sell the oldest stock first to avoid losses from spoilage. Short numerical example with the same data: first, the 100 units from opening inventory at $10 go out, then 200 units from the purchase at $12. Cost of sales = 100 × $10 + 200 × $12 = $1000 + $2400 = $3400. The remaining 200 units come from the $15 purchase: ending inventory = 200 × $15 = $3000. Check that $3400 + $3000 = $6400.

LIFO method (last in, first out)

LIFO, known in Spanish as UEPS (últimas entradas, primeras salidas), applies the opposite assumption: the last units to enter are the first to leave. Each issue is deducted from the most recent batches and the oldest batches remain in the warehouse. It is worth saying this clearly but carefully: in several countries it is not accepted under international standards, because IFRS do not allow LIFO for the presentation of financial statements; only in some countries with their own local rules, such as the United States under US GAAP, is it still in use. Before considering this method, check what your country's regulations allow and talk to your accountant. With rising prices, LIFO produces the highest cost of sales, because issues are valued at the recent, more expensive costs, and therefore gross profit is the lowest of the period, with a smaller tax effect. Ending inventory is valued at the old costs, which can lag behind the real replacement price and show an understated asset on the balance sheet. Short numerical example with the same data: first the 200 units from the $15 purchase go out, then 100 units from the $12 purchase. Cost of sales = 200 × $15 + 100 × $12 = $3000 + $1200 = $4200. The remaining stock is 100 units from opening inventory at $10 and 100 units from the $12 purchase: ending inventory = 100 × $10 + 100 × $12 = $1000 + $1200 = $2200. Check that $4200 + $2200 = $6400.

Quick comparison of the methods

The following table summarizes the essential differences between the three inventory valuation methods:

Method	How it calculates the cost of issues	Typical effect on cost of sales	When to use it
Weighted average	Divides the total cost available by the total units	Middle value: smooths out price changes	Homogeneous products, frequent purchases and a desire for stable results
FIFO (PEPS)	Issues the oldest units first	Lower when prices rise (higher profit)	Perishables or items with expiry dates; accepted under international standards
LIFO (UEPS)	Issues the most recent units first	Higher when prices rise (lower profit)	Only if your legislation allows it; not accepted in several countries under international standards

As you can see, the method does not change the physical merchandise or the total cost available: it changes when each cost is recognized as an expense and the value at which inventory is shown on the balance sheet.

The same case with all three methods

To keep the comparison fair, we now apply the three methods to the same case. These are the starting data:

Item	Units	Unit cost	Total cost
Opening inventory	100	$10	$1000
Purchase 1	200	$12	$2400
Purchase 2	200	$15	$3000
Total available	500	—	$6400
Sales for the period	300	—	—
Ending inventory (in units)	200	—	—

With those same figures, the three methods give the following results:

Method	Cost of sales (300 units)	Ending inventory (200 units)	Check total
Weighted average	$3840	$2560	$6400
FIFO (PEPS)	$3400	$3000	$6400
LIFO (UEPS)	$4200	$2200	$6400

Look at the check column: in all three cases the total is $6400, because the available cost does not change; only the split between cost of sales and ending inventory changes. This property is very useful in practice: if cost of sales plus ending inventory does not match the total cost available, there is an error in the calculation. Also notice the expected order in a rising-price scenario: the lowest cost of sales comes from FIFO ($3400) and the highest from LIFO ($4200), while the weighted average lands in the middle ($3840).

How to choose an inventory valuation method

There is no perfect method for every business, but there is an orderly way to decide. These are the criteria to review, in order:

Applicable standards: first check which methods your country's regulations accept. IFRS allow the weighted average and FIFO, but not LIFO; this point is non-negotiable because it defines which options you actually have.
Type of product: if you handle perishables or items with expiry dates, FIFO reflects the physical flow better and makes it easier to track how old the remaining stock is.
Desired stability in results: the weighted average smooths out sharp price changes and prevents one expensive purchase from distorting a single period's profit.
Operational simplicity: the average needs only one unit cost to value everything; FIFO and LIFO require tracking by cost lot or layer, which demands a more detailed record.
Tax effect: each method produces a different profit and therefore a different tax, but it should not be the only criterion: what you save today can cost you dearly in consistency and in an audit.
Consistency: once chosen, always apply it the same way. Changing methods is possible, but it must be justified, documented and disclosed in the financial statements.

For most small and medium businesses the practical decision comes down to weighted average or FIFO: both are internationally accepted, easy to explain and easy to audit. The final choice should be made by your accountant based on the company's activity, because the method directly affects the reported profit and the inventory value on the balance sheet.

The link between the kardex and the valuation method

The kardex, also called the inventory card or perpetual inventory record, logs every receipt, every issue and the running balance of units and values for a product. The valuation method is what tells the kardex which cost to record on each movement: under the weighted average, the unit cost is recalculated whenever new merchandise arrives, so the balance is updated with the new average; under FIFO and LIFO, each issue is deducted from the cost layer that corresponds according to the chosen order, consuming the oldest or the newest batch first depending on the case. That is why the method and the kardex cannot work separately: first you define the valuation policy and then the kardex applies it line by line. If the kardex says one thing and the method says another, the cost of sales does not tie out, the ending inventory does not match the physical count and the financial statements lose reliability. Keeping this record by hand in Excel or on paper makes the process slow and error-prone: one wrongly calculated cost on a single issue is enough to throw the whole balance off. That is why it helps to use inventory software with an integrated kardex, such as Kardex Tauro, which automatically applies the method you configure on every receipt and issue, keeps the balance always in check and leaves you an auditable record of each movement. This way, inventory valuation stops being a headache and becomes a reliable process that supports your accounting decisions.

Labels:

#fifo #lifo #inventory valuation