LIFO (Last In, First Out): Definition

What Is LIFO (Last In, First Out)?

LIFO is one of several methods used to assign costs to inventory as items are issued from stock. The method matters because items in inventory are rarely all purchased at the same price. When prices change over time, the assumption about which items were "used first" affects both the recorded cost of goods sold and the balance sheet value of remaining inventory.

Under LIFO, when an item is issued from inventory, the accounting system assigns the cost of the most recently purchased units to that issue. Older, earlier purchases remain in the inventory balance. This is the reverse of FIFO, which assigns the cost of the oldest units to each issue and leaves the most recent purchases in inventory.

LIFO is not generally how physical inventory works in practice. Leaving the oldest stock in place and always issuing the newest creates obvious problems: items at the back of a shelf deteriorate, consumables expire, and parts may become obsolete while newer units are consumed in front of them. LIFO is primarily a tax and accounting strategy, not a physical stock management practice. A company can apply LIFO cost flow assumptions in its financial statements while still physically managing inventory on a FIFO basis.

LIFO, FIFO, and Weighted Average: A Comparison

Three inventory costing methods are most commonly used. Each produces different values for cost of goods sold and ending inventory, with significant implications for reported profit and tax liability in periods of price change.

In a deflationary environment (falling purchase prices), the effects reverse: LIFO produces lower COGS and higher inventory values than FIFO. In stable price environments, the three methods produce similar results.

The LIFO Reserve

The LIFO reserve is the cumulative difference between the inventory value reported under LIFO and what it would be under FIFO. In a long-established company operating in an inflationary environment, the LIFO reserve can grow very large over time.

Financial analysts typically add the LIFO reserve back to LIFO-based inventory values when comparing a LIFO-reporting company against FIFO-reporting competitors, to produce a like-for-like comparison of balance sheet inventory values. The existence of a large LIFO reserve signals that reported inventory on the balance sheet significantly understates current replacement cost.

LIFO and Tax Strategy

LIFO's primary practical benefit for U.S. companies is the reduction of taxable income in inflationary periods. By matching the highest recent purchase costs against current revenue, LIFO increases reported cost of goods sold and reduces reported pretax profit. The tax savings represent a real cash benefit: lower taxes paid today have a present value even if future tax payments increase when the LIFO inventory is eventually liquidated.

This tax benefit comes with a cost: the "LIFO conformity rule" under U.S. tax law requires that any company using LIFO for tax purposes must also use LIFO for its primary financial reporting. A company cannot use LIFO to reduce its tax bill while reporting higher profits under FIFO to shareholders.

LIFO in Spare Parts and Maintenance Inventory

For maintenance and MRO spare parts, physical inventory management practice almost universally follows FIFO or a first-expire-first-out (FEFO) approach rather than LIFO. The reason is straightforward: spare parts can deteriorate, expire, or become obsolete if left in storage while newer receipts are consumed in front of them. Rubber seals degrade. Lubricants expire. Electronic components are superseded by newer designs. Issuing from the back of the bin first ensures the oldest stock is used before deterioration sets in.

For inventory accounting purposes, a facility can choose whichever cost flow method is most appropriate for its financial reporting: LIFO, FIFO, or weighted average. This accounting choice is independent of physical stock rotation practice. A storeroom that always physically issues the oldest unit on the shelf can still use LIFO cost flow assumptions in its inventory management system and accounts if that is the organization's policy for financial reporting.

In practice, most CMMS systems default to FIFO or weighted average cost for spare parts inventory control because these methods more accurately reflect the physical flow of goods and produce more accurate per-unit cost tracking for work order costing.

LIFO vs. FIFO: A Worked Numerical Example

To see how LIFO and FIFO produce different financial results, consider a maintenance storeroom that purchases a specific bearing at three different prices over a quarter and then issues four units to a work order.

Purchases: 2 units at $100 each (January), 2 units at $120 each (February), 2 units at $140 each (March). Total: 6 units on hand.

Issue: 4 units issued to a work order in April.

LIFO produces $80 more in COGS than FIFO ($520 vs $440), which reduces reported profit by $80 and reduces the taxable income by the same amount. At a 25 percent tax rate, that is $20 in immediate tax savings. The trade-off: the ending inventory on the balance sheet is valued at $200 under LIFO versus $280 under FIFO, a $80 understatement. Over decades, and with larger price increases, this gap compounds into the LIFO reserve.

LIFO Liquidation

A LIFO liquidation occurs when inventory quantities fall below the oldest LIFO cost layers. This happens when a company sells or uses more inventory than it purchases in a period, drawing down stock into the older, lower-cost layers at the bottom of the LIFO stack.

The effect is counterintuitive. When old, low-cost LIFO inventory layers are charged to COGS, the cost of goods sold falls even though current replacement costs have not changed. This produces artificially high reported profit in the period of the liquidation, a one-time earnings boost that does not reflect operational improvement. If the company is profitable, it also creates an unexpected tax liability on that inflated profit.

LIFO liquidations can occur involuntarily (supply disruptions, supplier delays, or demand spikes that force inventory drawdowns) or as a deliberate strategy (delaying purchases to push profits into a high-cash period). Securities analysts adjust for LIFO liquidation effects when modeling earnings quality, because they distort period-to-period comparisons. Footnote disclosures in U.S. GAAP financial statements are required when a LIFO liquidation has a material effect on earnings.

Why LIFO Is Prohibited Under IFRS

LIFO is not permitted under International Financial Reporting Standards (IFRS), which are used in over 140 countries outside the United States. IFRS requires inventory to be measured at the lower of cost and net realizable value, using either FIFO or the weighted average cost method.

The prohibition reflects several concerns: LIFO balance sheet values are systematically understated in inflationary environments, making cross-company comparisons misleading. The LIFO conformity rule creates an incentive for companies to adopt LIFO primarily for tax reasons rather than because it accurately reflects actual inventory flow. And the mismatch between LIFO-based balance sheet values and actual inventory replacement costs reduces the reliability of financial statements for investment analysis.

U.S. companies that report under GAAP and use LIFO but have significant international operations may need to present supplemental FIFO-basis disclosures to meet IFRS requirements for foreign subsidiaries or to facilitate comparison with international competitors.

Frequently Asked Questions

The Bottom Line

LIFO is primarily a tax and financial reporting method, not a physical inventory management practice. Its practical value is the reduction of taxable income in inflationary periods, achieved by matching the most recent and typically highest purchase costs against current revenue. This benefit is real for U.S. companies, but comes with the cost of understated balance sheet inventory values and restrictions on financial reporting format.

For maintenance and spare parts professionals, the more operationally relevant question is physical stock rotation: ensuring that the oldest spare parts are used before newer receipts, regardless of what cost flow method the accounting system uses. FIFO physical rotation prevents deterioration and obsolescence in the storeroom and produces more accurate per-job cost tracking when linked to work orders in the CMMS.