Inventory Methods Comparison: FIFO, LIFO, and Weighted Average for the CPA Exam
Compare FIFO, LIFO, and weighted-average inventory methods for the CPA FAR exam. Learn cost flow assumptions, effects on financial statements, and the LIFO reserve.
Inventory Cost Flow Assumptions
Inventory accounting is a foundational topic on the CPA FAR exam. Under ASC 330 (Inventory), entities must choose a cost flow assumption to determine the cost of goods sold and the cost of ending inventory. The three primary methods are first-in, first-out (FIFO), last-in, first-out (LIFO), and weighted average. Each method produces different results for cost of goods sold, ending inventory, and net income when inventory costs are changing.
FIFO (First-In, First-Out)
Under FIFO, the oldest costs are assigned to cost of goods sold and the most recent costs remain in ending inventory. This means that in a period of rising prices, FIFO produces the lowest cost of goods sold, the highest gross profit, and the highest ending inventory valuation among the three methods.
FIFO is generally considered to produce a balance sheet that more closely approximates current replacement cost because ending inventory consists of the most recently purchased items. However, the income statement under FIFO matches older costs against current revenues, which may not reflect the current cost structure.
FIFO Under Periodic and Perpetual Systems
An important exam concept: FIFO produces the same results under both periodic and perpetual inventory systems. Since the oldest costs are always removed first, the timing of the calculation does not affect the outcome.
LIFO (Last-In, First-Out)
Under LIFO, the most recent costs are assigned to cost of goods sold and the oldest costs remain in ending inventory. In a period of rising prices, LIFO produces the highest cost of goods sold, the lowest gross profit, and the lowest ending inventory valuation.
LIFO is often chosen for tax purposes because it minimizes taxable income when prices are rising. However, the LIFO conformity rule requires that if LIFO is used for tax purposes, it must also be used for financial reporting. A significant drawback is that the balance sheet may contain inventory valued at very old costs that do not reflect current economic reality.
LIFO Reserve
The LIFO reserve is the difference between inventory valued under FIFO and inventory valued under LIFO. Entities using LIFO must disclose the LIFO reserve or the amount by which inventory would change if valued under FIFO. This disclosure allows financial statement users to convert LIFO financial statements to a FIFO basis for comparability.
LIFO Liquidation
A LIFO liquidation occurs when a company sells more units than it purchases during a period, dipping into older LIFO layers. This can result in older, lower costs being matched against current revenues, artificially inflating gross profit. Companies must disclose the effect of LIFO liquidation on income when it is material.
Dollar-Value LIFO
Dollar-value LIFO is a variation that measures LIFO layers in dollar terms rather than in units. Inventory is grouped into pools, and layers are added or removed based on changes in the total dollar value of the pool adjusted for price changes using a price index. This method simplifies the application of LIFO when a company carries many different inventory items.
Weighted-Average Method
Under the weighted-average method, a single average cost is computed for all units available for sale during the period. Cost of goods sold and ending inventory are both valued at this average cost. The weighted-average cost is recalculated each time a purchase is made under the perpetual system (moving average) or computed once at the end of the period under the periodic system.
Note: Unlike FIFO, the weighted-average method produces different results under periodic and perpetual systems. Under a perpetual system, the moving-average cost is updated with each purchase, so the cost assigned to units sold depends on the timing of sales.
Lower of Cost or Net Realizable Value
Regardless of the cost flow method, ASC 330 requires inventory to be reported at the lower of cost or net realizable value (NRV) for entities using FIFO or weighted average. NRV is the estimated selling price minus reasonably predictable costs of completion, disposal, and transportation. For entities using LIFO or the retail inventory method, inventory is reported at the lower of cost or market, where market is replacement cost bounded by a ceiling (NRV) and a floor (NRV minus normal profit margin).
Effects on Financial Statements
During periods of rising prices:
- FIFO: Highest ending inventory, lowest COGS, highest net income, highest taxes
- LIFO: Lowest ending inventory, highest COGS, lowest net income, lowest taxes
- Weighted average: Results fall between FIFO and LIFO
During periods of falling prices, these relationships reverse.
Exam Preparation Tips
- Be able to compute cost of goods sold and ending inventory under all three methods for both periodic and perpetual systems.
- Understand how FIFO gives the same results under both systems but LIFO and weighted average do not.
- Know the LIFO conformity rule and the disclosure requirement for the LIFO reserve.
- Understand the lower of cost or NRV rule and how it differs for LIFO entities.
- Watch for LIFO liquidation questions; they are a common trap on the exam.
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