Explain FIFO and LIFO. In a period of rising prices, which method produces higher reported net income, and why?

What the interviewer is actually testing

Inventory method questions test whether you understand the causal chain from an accounting policy choice to every financial statement effect, not just "FIFO is high, LIFO is low" as memorized trivia.

1. You can derive, not just recite, the direction of the FIFO/LIFO effects. The strongest candidates reason from first principles: prices are rising, so the newest units cost more; LIFO expenses those newest units first, so COGS is higher and profit is lower under LIFO. Reciting "FIFO equals higher income, LIFO equals lower income" without being able to explain why falls apart the moment the interviewer flips the scenario to a period of falling prices, where the effects reverse.

2. You immediately connect the income statement effect to the balance sheet and cash flow. The complete answer does not stop at gross margin -- it continues to explain that because LIFO reports lower taxable income, the company pays lower cash taxes, which is a real cash flow benefit despite the lower reported earnings. This is the single most-tested insight in the topic and the fastest way to signal seniority.

3. You know the LIFO reserve exists and what it is for. Being asked to convert a LIFO-basis company to a FIFO-equivalent basis, or vice versa, for comparison purposes is a classic elite-boutique question, especially in industrials, retail, and commodity-adjacent coverage groups where LIFO is common (oil and gas, industrials, some retailers).

4. You can connect gross margin to the qualitative story of the business. A strong answer to "what does gross margin tell you" goes beyond the formula to explain that it reflects pricing power, input cost control, product mix, and scale economies -- and that comparing gross margin across companies only works if their inventory accounting policies are consistent, or adjusted to be comparable.

Keep the mechanical walk-through crisp -- most of the differentiation happens in the follow-ups about deflationary environments, LIFO liquidation, and reserve adjustments.

Common traps

Trap 1: Memorizing the direction without understanding it depends on the price environment. Candidates state "FIFO always means higher profit" as an absolute rule. It is only true when prices are rising; in a deflationary environment the effects flip completely.

Say it out loud: The direction depends on the price trend -- in a rising-price environment FIFO produces lower COGS and higher profit than LIFO, but if input costs are falling, LIFO would instead produce the lower COGS and higher profit.

Trap 2: Forgetting the tax and cash flow consequence entirely. Candidates describe the income statement effect of LIFO vs. FIFO but never mention that the difference in reported income changes the actual cash tax bill -- which is the real-world reason the choice matters.

Say it out loud: The accounting choice isn't just cosmetic -- LIFO's lower reported income in an inflationary environment means a lower current tax bill, which is real cash saved, not just a different number on a page.

Trap 3: Assuming IFRS allows LIFO. Some candidates apply US GAAP intuition universally and assume any company, anywhere, can choose LIFO. IFRS explicitly prohibits LIFO.

Say it out loud: LIFO is a US GAAP-only option -- IFRS prohibits it, so only FIFO and weighted-average cost are available under IFRS, which is one reason cross-border comps sometimes need a LIFO-to-FIFO adjustment.

Trap 4: Confusing which method leaves ending inventory closer to current replacement cost. Candidates sometimes say LIFO gives a more "up to date" balance sheet. It is the opposite -- FIFO leaves the most recent costs in ending inventory, while LIFO can leave decades-old cost layers on the balance sheet.

Say it out loud: FIFO leaves ending inventory valued near current replacement cost since the newest purchases remain unsold on paper; LIFO can leave inventory carried at old, stale cost layers that understate its true current value.

Trap 5: Ignoring the LIFO reserve when comparing companies. Candidates compare a LIFO company's gross margin directly against a FIFO peer's without adjusting, producing a distorted read on which company is actually more efficient.

Say it out loud: Before comparing gross margins across a LIFO company and a FIFO company, I'd add back the change in the LIFO reserve to the LIFO company's COGS, or equivalently restate its inventory and COGS to a FIFO-equivalent basis, so the comparison isn't distorted by accounting policy.

Trap 6: Treating an inventory write-down as a cash expense. Candidates model an inventory impairment as reducing cash directly. It's a non-cash charge -- it reduces the inventory asset and pre-tax income, but no cash actually moves at the time of the write-down.

Say it out loud: An inventory write-down is non-cash -- it reduces the carrying value of inventory and hits pre-tax income, but the cash was already spent when the inventory was originally purchased or produced.