FIFO vs LIFO Inventory: How Each Method Changes Your Profit and Taxes
FIFO vs LIFO inventory costing decides which costs land in your books when a unit sells, not which physical box leaves the shelf. Both are cost-flow assumptions. You pick one, apply it consistently, and it flows straight into your cost of goods sold (COGS), your gross profit, and the tax you owe.
The two methods sound like a technicality. They are not. On the same sales, in the same month, they can hand you a different profit number and a different tax bill. Here is exactly how, with numbers you can copy.
FIFO vs LIFO inventory: the short version
- FIFO (First In, First Out): the oldest cost is expensed first. Your remaining inventory carries the newest, usually higher, costs.
- LIFO (Last In, First Out): the newest cost is expensed first. Your remaining inventory carries the oldest, usually lower, costs.
That is the entire mechanism. Everything else is a consequence of it, and the consequences get big fast when your purchase prices move.
One thing to nail down up front: this is about which cost you record, not which item you physically ship. You can run FIFO on paper while your warehouse pulls stock in whatever order makes sense. Cost flow and physical flow are separate decisions, and we will come back to that.
A worked example with real numbers
Say you buy the same SKU three times as your supplier keeps nudging prices up:
| Purchase | Units | Unit cost | Total |
|---|---|---|---|
| January | 100 | $10 | $1,000 |
| February | 100 | $12 | $1,200 |
| March | 100 | $14 | $1,400 |
| On hand | 300 | $3,600 |
Now you sell 150 units at $20 each, so revenue is $3,000. Same sale, two costing methods.
FIFO expenses the oldest costs first:
COGS = (100 x $10) + (50 x $12) = $1,000 + $600 = $1,600
LIFO expenses the newest costs first:
COGS = (100 x $14) + (50 x $12) = $1,400 + $600 = $2,000
Same 150 units out the door, a $400 gap in COGS. That gap is the whole story.
What actually changes on your financials
Here is the same sale run all the way through, side by side:
| Line | FIFO | LIFO |
|---|---|---|
| Revenue | $3,000 | $3,000 |
| COGS | $1,600 | $2,000 |
| Gross profit | $1,400 | $1,000 |
| Ending inventory | $2,000 | $1,600 |
When prices are rising, the pattern is always the same:
- FIFO reports higher profit and a higher inventory value on the balance sheet. It also means higher taxable income, so a bigger tax bill.
- LIFO reports lower profit and lower taxable income, so you defer tax. The trade-off is an inventory value on your balance sheet that can drift far below what the stock is actually worth.
That last point matters. Under LIFO your balance sheet can still be carrying units at that old $10 cost years later, long after replacement cost has doubled. Accountants call the buried gain a "LIFO reserve," and it is one reason the method draws scrutiny.
If prices are falling, everything flips: FIFO produces the lower profit and LIFO the higher one. LIFO is only a tax play while your costs keep climbing.
Where weighted average sits
There is a quieter third option: weighted average cost. You blend every purchase into one average and expense that.
Average cost = $3,600 / 300 = $12.00 per unit
COGS = 150 x $12.00 = $1,800
Gross profit = $1,200
It lands neatly between FIFO and LIFO, and it smooths out price swings. For a lot of businesses it is the least fussy answer, which is why it is common in manufacturing and anywhere costs bounce around.
The rule that decides it for most of the world
Before you spend an afternoon modeling LIFO, check whether you are even allowed to use it.
IFRS bans LIFO. US GAAP allows it. So if you report under IFRS, which is most countries outside the United States, LIFO is off the table entirely and the real choice is FIFO versus weighted average.
In the US, LIFO is legal but comes with the LIFO conformity rule: if you use it on your tax return, you generally have to use it in your financial statements too. You do not get to show investors a fat FIFO profit and hand the tax authority a lean LIFO one. Pick your poison and live in it.
Physical flow is a separate question (FIFO and FEFO)
Costing is an accounting decision. How stock actually moves through your warehouse is an operations decision, and for most goods you want the oldest units leaving first no matter what costing method you run. Old stock gets damaged, goes out of style, or quietly rots.
For anything dated or perishable, oldest-first becomes FEFO (First Expired, First Out), which sequences by expiry date rather than receipt date. A batch that arrived later but expires sooner should ship first. Food, cosmetics, pharma, and chemicals live and die by this.
The practical takeaway: run FIFO or FEFO on the floor to protect the product, then choose your costing method for the books based on tax and reporting. They do not have to match, and confusing the two is where a lot of teams tie themselves in knots.
Which method should you pick?
Work through it in order:
- Check your reporting standard. IFRS means no LIFO. That decision may already be made for you.
- Look at your price trend. Steadily rising costs plus a US tax return is the only scenario where LIFO's tax deferral really pays. Flat or volatile costs weaken the case fast.
- Weigh the admin cost. LIFO adds layers, reserves, and disclosures. If you are small, the tax savings often do not cover the accounting headache.
- Think about your balance sheet. If you need inventory to reflect real, current value (raising money, applying for credit, planning a sale), FIFO tells a cleaner story.
- Default to FIFO or weighted average unless a specific, quantified LIFO tax benefit justifies the complexity. Most businesses land here, and honestly, they should.
Whatever you choose, apply it consistently. Switching methods to flatter a quarter is exactly the kind of thing auditors and tax authorities are paid to notice.
Where Inventoros fits
Whichever costing method you settle on, the hard part is tracking cost layers accurately across every purchase, every location, and every sale, so your COGS is real instead of a spreadsheet guess. Inventoros records receipts with their costs, moves stock across multiple locations, and exposes it all through a REST and GraphQL API so your accounting system can pull the exact numbers it needs. It is free, open source, and self-hosted, so the cost data behind your books stays on infrastructure you own. The documentation walks through install on cPanel, a VPS, or Docker.
FAQ
Is FIFO or LIFO better for taxes? In a rising-price environment, LIFO usually lowers your taxable income by pushing higher recent costs into COGS, so it defers tax. That only works if your costs keep climbing, you report under US GAAP, and you accept the LIFO conformity rule. If costs are flat or falling, LIFO offers no tax edge and FIFO may even beat it.
Why is LIFO banned under IFRS? IFRS regulators view LIFO as a distortion. It can leave inventory on the balance sheet at costs from years ago that bear no relation to current value, and it rarely matches how goods physically move. Because most countries follow IFRS, LIFO is effectively a US-only method.
Does FIFO mean I have to ship my oldest stock first? No. FIFO as a costing method is only about which cost you expense, not which unit you pick. That said, shipping oldest stock first (FIFO, or FEFO for dated goods) is good warehouse practice on its own, so most teams do both. Just keep the two ideas separate in your head.
What about weighted average cost? Weighted average blends all your unit costs into one figure and expenses that on each sale. It smooths out price swings and is simpler to run than LIFO, with none of the IFRS restrictions. For many businesses it is the pragmatic middle ground between FIFO and LIFO.