Why does LIFO result in lower taxes than FIFO when prices are rising, and what is the cash flow impact?

The tax advantage of LIFO during inflation is one of the most important practical concepts in inventory accounting. Let me demonstrate with concrete numbers.

Scenario:

Westbrook Hardware buys screwdriver sets in three batches during 2025:

Westbrook sells 450 units during 2025 at $18 each. Revenue = $8,100. Tax rate = 25%.

Under FIFO (first units purchased are sold first):

COGS = (200 x $8) + (200 x $9.50) + (50 x $11) = $1,600 + $1,900 + $550 = $4,050

Gross profit = $8,100 - $4,050 = $4,050

Tax = $4,050 x 25% = $1,012.50

Under LIFO (last units purchased are sold first):

COGS = (200 x $11) + (200 x $9.50) + (50 x $8) = $2,200 + $1,900 + $400 = $4,500

Gross profit = $8,100 - $4,500 = $3,600

Tax = $3,600 x 25% = $900

Tax savings from LIFO = $1,012.50 - $900 = $112.50

Cash flow impact:

Both methods involve the same physical units and the same cash outflows for purchases. The only difference is the tax payment. Under LIFO, Westbrook pays $112.50 less in taxes, keeping that cash in the business. This is a real economic benefit, not just an accounting illusion.

The LIFO Conformity Rule (US GAAP only):

Under the IRS LIFO conformity rule, if a company uses LIFO for tax purposes, it must also use LIFO for its primary financial statements. This means companies cannot use LIFO on the tax return (to save taxes) while showing higher FIFO profits to shareholders. They must accept the lower reported profits in exchange for the tax savings.

IFRS note: IFRS prohibits LIFO entirely. Companies reporting under IFRS must use FIFO or weighted average cost. This is one of the most important GAAP vs. IFRS differences tested on CFA Level I.

When does LIFO backfire? If prices are falling, LIFO produces higher COGS from older, more expensive inventory layers — resulting in HIGHER taxes. Also, LIFO liquidation (dipping into old, low-cost layers) can create unexpected tax bills.

Explore more inventory tax scenarios in our CFA Level I practice questions.