Inventory Valuation Methods: FIFO, LIFO & Weighted Average Under GAAP

Published: March 27, 2026
Ryan O'Connell, CFA, FRM
Article by Ryan O'Connell, CFA, FRM

Inventory is often the largest current asset on a manufacturer’s or retailer’s balance sheet, and the valuation method a company chooses under GAAP directly determines both Cost of Goods Sold (COGS) on the income statement and ending inventory on the balance sheet. For a company like Caterpillar, whose 2023 10-K disclosed a LIFO reserve exceeding $3 billion, the choice between FIFO, LIFO, and weighted average is one of the most consequential accounting policy decisions management makes. This guide covers every major inventory valuation method under U.S. GAAP, how each affects financial statements, and the analytical adjustments needed to compare companies that use different methods.

What Are Inventory Valuation Methods?

Under U.S. GAAP (ASC 330), companies must assign a cost to both ending inventory and cost of goods sold using a systematic cost flow assumption. Critically, the cost flow assumption does not need to match the physical flow of goods through the warehouse.

Key Concept

A cost flow assumption determines which costs are allocated to COGS and which remain in ending inventory. GAAP permits four methods: FIFO (First-In, First-Out), LIFO (Last-In, First-Out), weighted average cost, and specific identification. LIFO is the only method prohibited under IFRS (IAS 2) — FIFO, weighted average, and specific identification are all permitted under both frameworks.

Companies also choose between two inventory tracking systems:

  • Periodic system — inventory and COGS are calculated only at the end of each accounting period via physical count
  • Perpetual system — inventory is updated continuously after each purchase and sale transaction

Under FIFO, both systems always produce identical results. Under LIFO and weighted average, however, periodic and perpetual systems can produce materially different COGS and ending inventory figures. All examples in this article use the periodic system unless otherwise noted. For how inventory levels affect the cash conversion cycle and working capital management, see our dedicated guide.

First-In, First-Out (FIFO)

Under FIFO, the oldest inventory costs are assigned to COGS first, while the most recently purchased costs remain in ending inventory. This means the balance sheet inventory figure closely approximates current replacement cost.

FIFO Ending Inventory
Ending Inventory = Units Remaining × Most Recent Purchase Costs (in layers)
Work backward from the most recent purchase to fill the remaining units on hand
Cascade Industrial Supply — FIFO Calculation

Cascade Industrial Supply, a wholesale distributor of industrial hardware, had the following inventory activity during Q1:

Purchase Units Unit Cost Total Cost
Beginning inventory 2,000 $4.00 $8,000
March 15 purchase 6,000 $4.40 $26,400
March 30 purchase 2,000 $4.75 $9,500
Total available 10,000 $43,900

Cascade sold 4,000 units during Q1, leaving 6,000 units on hand.

FIFO COGS: 2,000 × $4.00 + 2,000 × $4.40 = $8,000 + $8,800 = $16,800

FIFO Ending Inventory: 4,000 × $4.40 + 2,000 × $4.75 = $17,600 + $9,500 = $27,100

Pro Tip

LIFO is the only cost flow assumption prohibited under IFRS. If your company has international operations or plans to adopt IFRS reporting, FIFO and weighted average both eliminate a future accounting conversion. FIFO’s ending inventory also provides the most useful balance sheet figure because it reflects the most recent purchase prices.

Last-In, First-Out (LIFO)

Under LIFO, the most recently purchased inventory costs are assigned to COGS first, while the oldest costs remain in ending inventory. This produces a COGS figure that closely reflects current replacement costs but leaves ending inventory at potentially outdated prices.

IFRS Prohibition

LIFO is prohibited under IFRS (IAS 2). It is permitted only under U.S. GAAP (ASC 330). Companies preparing IFRS financial statements cannot use LIFO, making this one of the most significant remaining differences between the two frameworks.

LIFO Ending Inventory (Periodic)
Ending Inventory = Oldest Units × Oldest Purchase Costs (in layers)
Under periodic LIFO, assume the most recent purchases are sold first; ending inventory comes from the earliest purchase layers
Cascade Industrial Supply — LIFO Calculation

Using the same Q1 data (10,000 units available, 4,000 sold):

LIFO COGS: 2,000 × $4.75 + 2,000 × $4.40 = $9,500 + $8,800 = $18,300

LIFO Ending Inventory: 2,000 × $4.00 + 4,000 × $4.40 = $8,000 + $17,600 = $25,600

Compared to FIFO, LIFO produces $1,500 higher COGS and $1,500 lower ending inventory — a direct consequence of assigning the most recent (and highest) costs to COGS.

LIFO Liquidation Risk

When a LIFO company sells more units than it purchases during a period, it dips into old, low-cost inventory layers. These cheap costs flow to COGS, artificially reducing COGS and overstating gross profit and net income. Analysts flag potential LIFO liquidation by watching for a year-over-year decrease in the LIFO reserve, though deflation and inventory mix changes can also reduce the reserve.

LIFO conformity rule: Under U.S. tax law, a company that uses LIFO for tax purposes must also use LIFO for its GAAP financial statements. This requirement is the primary reason many U.S. manufacturers adopted LIFO — the tax savings from lower taxable income in inflationary periods require simultaneous use in financial reporting.

Dollar-Value LIFO

Dollar-value LIFO measures inventory changes in total dollar terms rather than physical units. It uses a price index to separate real quantity changes from price inflation, allowing companies to maintain broader inventory pools and reduce the risk of LIFO liquidation. This is the most commonly used LIFO variant in practice and is frequently tested on the CPA exam.

Retail Inventory Method

The retail inventory method is a separate cost-estimation technique (not a cost flow assumption) used by retailers with large numbers of inventory items. It maintains records at both cost and retail prices and applies a cost-to-retail ratio to estimate ending inventory at cost. The conventional retail method approximates LCNRV. While not itself a LIFO method, retailers can combine it with LIFO cost flow assumptions. For the economic distinction between GAAP cost allocation and production cost curves in microeconomics, see our dedicated guide.

Weighted Average Cost

The weighted average cost method assigns every unit the same average cost per unit, computed by dividing the total cost of goods available for sale by the total number of units available.

Weighted Average Cost Per Unit
WAC = Total Cost of Goods Available ÷ Total Units Available
This single average cost applies equally to all units sold and all units remaining in inventory
Weighted Average Ending Inventory
Ending Inventory = Units Remaining × WAC Per Unit
The same per-unit cost used for COGS also values ending inventory
Cascade Industrial Supply — Weighted Average Calculation

Using the same Q1 data (10,000 units, $43,900 total cost):

WAC per unit: $43,900 ÷ 10,000 = $4.39

COGS: 4,000 × $4.39 = $17,560

Ending Inventory: 6,000 × $4.39 = $26,340

Under a perpetual system, weighted average becomes a moving weighted average — recalculated after every purchase. The moving average produces different COGS and ending inventory figures than the periodic weighted average because the per-unit cost is updated with each new purchase before sales are costed.

LIFO Reserve & Converting Between Methods

Companies that use LIFO are required to disclose the LIFO reserve in their financial statement footnotes, enabling analysts to convert LIFO figures to a FIFO basis for cross-company comparisons.

Key Concept

The LIFO reserve is the cumulative difference between a company’s inventory valued under FIFO and its inventory valued under LIFO. In an inflationary environment, the LIFO reserve is always positive because FIFO ending inventory exceeds LIFO ending inventory.

LIFO Reserve
LIFO Reserve = FIFO Inventory − LIFO Inventory
The reserve represents the cumulative effect of using LIFO instead of FIFO on the balance sheet

Using the Cascade Industrial Supply example: LIFO Reserve = $27,100 − $25,600 = $1,500.

Converting LIFO COGS to FIFO COGS
FIFO COGS = LIFO COGS − Δ LIFO Reserve
If the LIFO reserve increased during the period, LIFO COGS was higher than FIFO COGS by that amount

When the LIFO reserve decreases year-over-year, it signals LIFO liquidation — old, low-cost layers have been consumed, and reported income is overstated relative to what FIFO would have produced.

Pro Tip

When comparing two companies where one uses FIFO and the other uses LIFO, add the LIFO reserve to the LIFO company’s inventory and increase retained earnings by the after-tax LIFO reserve (LIFO reserve × (1 − tax rate)). This adjustment affects the current ratio, working capital components, inventory turnover, and debt-to-equity ratio — producing the apples-to-apples comparison analysts require.

Lower of Cost or Net Realizable Value (LCNRV)

Under ASC 330 (and IAS 2), inventory must be written down when its net realizable value falls below its historical cost. This is the conservatism principle in action — losses are recognized in the period the decline occurs, not the period the inventory is eventually sold.

Key Concept

Inventory is carried at the lower of its historical cost or its net realizable value (NRV). NRV is the estimated selling price in the ordinary course of business minus estimated costs of completion and estimated costs to sell.

Net Realizable Value
NRV = Estimated Selling Price − Costs to Complete − Selling Costs
NRV represents the net amount the company expects to realize from selling the inventory
LIFO and Retail Inventory Method Exception

Post-ASU 2015-11, the LCNRV rule applies to companies using FIFO and weighted average. Companies using LIFO or the retail inventory method continue to apply the older lower of cost or market (LCM) framework, which uses replacement cost subject to a ceiling (NRV) and a floor (NRV minus normal profit margin). This distinction is frequently tested on the CPA exam.

LCNRV Write-Down Example

Cascade Industrial Supply has 500 units of a slow-moving SKU with a cost of $4.75 per unit. Due to oversupply in the market, the estimated selling price has dropped to $4.50 per unit, and estimated selling costs are $0.20 per unit.

NRV: $4.50 − $0.20 = $4.30 per unit

Since $4.30 < $4.75, inventory must be written down:

Write-down: ($4.75 − $4.30) × 500 = $225

Journal entry: debit Loss on Inventory Write-Down $225, credit Inventory (or Allowance to Reduce Inventory to NRV) $225. Under GAAP, this write-down cannot be reversed even if NRV subsequently recovers. IFRS permits reversal up to original cost.

Inventory Errors and Their Financial Statement Effects

Inventory errors are among the most consequential accounting mistakes because they affect both the income statement and the balance sheet — and they carry over into the next period.

Key Concept

An error in ending inventory flows directly into COGS (since COGS = Beginning Inventory + Purchases − Ending Inventory) and therefore into net income. Because this period’s ending inventory becomes next period’s beginning inventory, the error reverses in the following period — creating a two-period distortion pattern.

Error Effect on Current Period Effect on Next Period
Ending inventory overstated COGS understated, net income overstated COGS overstated, net income understated (self-corrects)
Ending inventory understated COGS overstated, net income understated COGS understated, net income overstated (self-corrects)

While inventory errors self-correct over two periods, both periods contain misstated financial statements. If the error is material, prior-period financial statements must be restated. Auditors specifically test inventory quantities and valuations because of the magnitude of these potential misstatements.

How to Calculate COGS and Ending Inventory

Here is a comprehensive side-by-side comparison of all three methods using the full Cascade Industrial Supply dataset. This is the format used in managerial accounting reports and CPA exam problems.

Cascade Industrial Supply — Full Method Comparison

Given: 10,000 units available for sale ($43,900 total cost). 4,000 units sold at $6.00 each ($24,000 revenue). 6,000 units remaining.

Metric FIFO LIFO Weighted Average
COGS $16,800 $18,300 $17,560
Ending Inventory $27,100 $25,600 $26,340
Gross Profit $7,200 $5,700 $6,440

All three methods allocate the same $43,900 total cost — the difference is entirely in the split between COGS and ending inventory. In this inflationary scenario (unit costs rising from $4.00 to $4.75), FIFO produces the highest ending inventory and lowest COGS, while LIFO produces the lowest ending inventory and highest COGS. Weighted average falls between the two.

Try the Inventory Valuation Calculator

FIFO vs LIFO vs Weighted Average

The choice between inventory valuation methods involves trade-offs across the income statement, balance sheet, tax impact, and regulatory compliance. Here is a structured comparison:

FIFO (First-In, First-Out)

  • Income statement: Lowest COGS and highest net income in inflation
  • Balance sheet: Ending inventory reflects current market prices
  • Tax impact: Highest taxes in inflationary periods
  • Permitted under both GAAP and IFRS
  • Best for perishables, technology, and fashion where physical FIFO is natural
  • Used by Apple, Costco, and most technology companies

LIFO (Last-In, First-Out)

  • Income statement: Highest COGS and lowest net income in inflation (better matching)
  • Balance sheet: Ending inventory may be severely understated (old cost layers)
  • Tax impact: Lowest taxes — primary advantage is tax deferral
  • U.S. GAAP only — prohibited under IFRS
  • Best for bulk commodities, steel, and petroleum
  • Used by ExxonMobil and General Motors (historically)

Weighted Average Cost

  • Income statement: COGS and net income fall between FIFO and LIFO
  • Balance sheet: Ending inventory is a blended average of all purchase prices
  • Tax impact: Middle ground between FIFO and LIFO
  • Permitted under both GAAP and IFRS
  • Best for interchangeable goods (grain, fuel, chemicals)
  • Used by beverage and chemical manufacturers

In deflationary environments, all rankings reverse — LIFO produces the highest income and FIFO the lowest. In a stable-price environment, all three methods converge toward approximately the same result.

Limitations of Inventory Valuation Methods

While cost flow assumptions are necessary for financial reporting, each method introduces specific distortions that users of financial statements should understand:

  1. LIFO balance sheet distortion: LIFO ending inventory can contain cost layers that are decades old, bearing no resemblance to current replacement values. Balance-sheet-based ratios (current ratio, inventory turnover) become misleading without LIFO reserve adjustment.
  2. Method lock-in under LIFO conformity: Switching away from LIFO requires IRS approval and triggers a taxable income catch-up in the year of change, creating a significant switching cost that discourages method changes even when LIFO no longer serves the company well.
  3. Weighted average obscures price trends: By pooling all costs into a single average, the method masks the direction of input cost pressure that FIFO’s layered ending inventory would reveal to analysts.
  4. Periodic vs. perpetual timing differences: LIFO and weighted average produce different results depending on which system is used, creating comparability issues even between companies using the same cost flow assumption.

For how other current asset valuations affect the same balance sheet ratios, see our accounts receivable and bad debt guide. For non-current asset valuation, see our depreciation methods article.

Common Mistakes

Watch Out

These are the most frequently tested mistakes on the CPA exam and the most common errors in real financial statement preparation. Each one can result in misstated COGS, ending inventory, and net income.

  1. Confusing cost flow assumption with physical flow: GAAP allows any cost flow assumption regardless of how goods physically move through the warehouse. A grocery store can use LIFO for accounting while rotating stock FIFO on the shelf. The cost flow is an accounting policy choice, not a description of physical movement.
  2. Using perpetual LIFO results for a periodic LIFO problem: Under periodic LIFO, all sales are assumed to occur at period-end after all purchases are known. Under perpetual LIFO, each sale uses the most recent cost at the moment of that sale. The results can differ materially — always identify which system the problem or company uses.
  3. Not considering the unit of account for LCNRV: ASC 330 permits LCNRV on an individual-item, major-category, or total-inventory basis — whichever most clearly reflects periodic income. However, applying LCNRV at the total-inventory level can mask item-level write-downs by allowing gains on some items to offset losses on others. Most companies use the item-by-item basis; always verify which level the company applies before interpreting its inventory valuation.
  4. Ignoring the LIFO reserve when comparing companies: Comparing a FIFO company’s current ratio to a LIFO company’s current ratio without adjusting for the LIFO reserve produces an apples-to-oranges comparison. The LIFO company’s inventory is understated relative to current replacement cost.
  5. Assuming an inventory error affects only one period: Inventory errors self-correct over two periods, but both periods contain misstated financials. An overstated ending inventory in Year 1 understates COGS (overstates income) in Year 1, then overstates COGS (understates income) in Year 2 when it becomes beginning inventory.

Frequently Asked Questions

There is no universally best method — the optimal choice depends on the company’s industry, tax strategy, and reporting goals. FIFO produces the most current balance sheet values and is permitted under both GAAP and IFRS, making it the default for international or multinational companies. LIFO is chosen primarily for its U.S. tax deferral benefit in inflationary environments. Weighted average suits companies with homogeneous, interchangeable inventory where individual unit tracking is impractical. Most U.S. retail and manufacturing companies use FIFO or weighted average; LIFO usage is concentrated in commodity-intensive industries.

Yes, but it is not simple. Under GAAP, a change in inventory method is a change in accounting principle under ASC 250, requiring the company to demonstrate that the new method is preferable. LIFO-to-FIFO switches are the most common and require IRS approval because of the LIFO conformity rule. The company must recognize the cumulative effect of the change, which for long-time LIFO users can produce a significant one-time tax liability as the LIFO reserve is unwound. The financial statements must also be retrospectively adjusted to reflect the new method in prior-period comparatives.

LIFO liquidation occurs when a LIFO company sells more units than it purchases during a period, forcing it to dip into old, low-cost inventory layers. Because those old costs are much lower than current replacement costs, COGS is artificially reduced and gross profit is overstated — giving the false impression of improved profitability. Analysts flag LIFO liquidation by watching for a decrease in the LIFO reserve from one period to the next. Companies sometimes avoid year-end LIFO liquidation by making strategic year-end inventory purchases to replenish layers.

No. IFRS (IAS 2) explicitly prohibits the use of LIFO. The IASB concluded that LIFO does not represent a faithful depiction of inventory flows and results in an outdated balance sheet. Any company reporting under IFRS — including most companies outside the United States — must use either FIFO, weighted average cost, or specific identification. This is one of the most significant remaining differences between U.S. GAAP and IFRS.

The choice of method directly affects several key ratios. Current ratio: FIFO produces a higher inventory balance than LIFO in inflation, increasing the current ratio. Inventory turnover: LIFO’s lower inventory denominator inflates the turnover ratio, making a LIFO company appear to manage inventory more efficiently than it actually does. Gross profit margin: FIFO’s lower COGS produces a higher gross margin in inflation. Debt-to-equity: LIFO’s lower retained earnings (from higher cumulative COGS) increases leverage ratios. Analysts always adjust LIFO financials using the LIFO reserve before comparing ratios across companies using different methods. See our accounts receivable and bad debt article for how other current asset valuations affect the same ratios.

A periodic system counts inventory and calculates COGS only at the end of each accounting period. A perpetual system updates inventory and COGS after every transaction. FIFO always produces identical results under both systems. LIFO and weighted average do not: under perpetual LIFO, each sale is costed using the most recent purchase price at that date, which can differ from periodic LIFO where all sales are assumed to occur after all purchases. Under a perpetual system, weighted average becomes a moving weighted average — recalculated after each purchase. For exam problems and financial analysis, always identify which system is being used. Use our Inventory Valuation Calculator to model different methods interactively.

Disclaimer

This article is for educational and informational purposes only and does not constitute accounting or tax advice. Inventory accounting rules are governed by ASC 330 (U.S. GAAP) and IAS 2 (IFRS); consult the authoritative standards and a licensed CPA for specific accounting guidance. Numerical examples are illustrative and based on Kieso, Weygandt & Warfield, Intermediate Accounting, 17th Edition (Wiley).