Inventory Valuation Methods: FIFO, LIFO, WAC, and How to Choose
Every unit sitting in your warehouse has a cost attached to it, and the method you use to assign that cost changes your reported profit, your tax bill, and the value on your balance sheet. Inventory valuation methods are the accounting rules that decide which cost lands in Cost of Goods Sold (COGS) when you make a sale and which cost stays in ending inventory. Pick one, apply it consistently, and the same set of purchases can produce very different numbers on your books.
This guide covers the four methods that matter, walks through one worked example so you can see the difference in dollars, and gives you a straight answer on how to choose.
What inventory valuation actually decides
When you buy stock at different prices over time, you end up with layers of cost. When you sell, you have to decide which layer to expense. That single decision drives three things:
- COGS on your income statement (higher COGS means lower gross profit)
- Ending inventory on your balance sheet (whatever cost you did not expense)
- Taxable income, because profit is what gets taxed
The two always tie back to one number. Beginning inventory plus purchases equals COGS plus ending inventory. If you push more cost into COGS, less stays in inventory, and the reverse. The methods below are just different rules for splitting that total.
The main inventory valuation methods
FIFO (First In, First Out)
FIFO assumes the oldest units sell first. The cost of your earliest purchases flows into COGS, and your newest costs stay in ending inventory. In a period of rising prices, FIFO gives you the lowest COGS, the highest reported profit, and the highest inventory value. It also mirrors how most physical goods actually move, especially anything perishable or with a shelf life.
LIFO (Last In, First Out)
LIFO assumes the newest units sell first. Your most recent (usually higher) costs hit COGS, leaving older, cheaper costs in inventory. When prices are rising, LIFO produces higher COGS, lower profit, and a lower tax bill, which is exactly why some US companies use it. One catch matters: LIFO is permitted under US GAAP but banned under IFRS, so it is off the table in most of the world.
Weighted Average Cost (WAC)
WAC ignores layers entirely. You blend every unit into one average cost and apply that average to both sales and remaining stock. It smooths out price swings, it is simple to run at scale, and it is the default in a lot of software because you do not have to track individual cost lots. The formula is:
Weighted average cost = total cost of goods available / total units available
Specific Identification
Specific identification tracks the exact cost of each individual item. When you sell that item, you expense its actual cost, no assumptions. This is the right method for serialized, high-value, or one-of-a-kind goods: cars, jewelry, custom equipment, art. It is precise, and impractical for anything you hold in bulk.
Worked example: same purchases, three different answers
Say you buy 300 units across a quarter as your supplier raises prices:
- January: 100 units at $10 = $1,000
- February: 100 units at $12 = $1,200
- March: 100 units at $15 = $1,500
Total: 300 units, $3,700 available. You sell 150 units at $20 each, so revenue is $3,000 and 150 units remain. Here is what each method reports.
| Method | COGS | Ending inventory | Gross profit |
|---|---|---|---|
| FIFO | $1,600 | $2,100 | $1,400 |
| WAC | $1,850 | $1,850 | $1,150 |
| LIFO | $2,100 | $1,600 | $900 |
FIFO expenses the cheap January and February units first (100 at $10 plus 50 at $12 = $1,600). LIFO expenses the pricey March units first (100 at $15 plus 50 at $12 = $2,100). WAC blends everything to $12.33 per unit and applies it both ways (150 at $12.33 = $1,850).
Same goods, same sales, and gross profit swings by $500 depending only on the accounting method. That $500 is real taxable income. Multiply it across thousands of SKUs and you can see why this is not a footnote.
How to choose an inventory valuation method
A few practical rules:
- Match the physical flow when you can. Perishables and dated stock lean FIFO because that is how they actually leave the shelf.
- Go WAC for volume and simplicity. If you move interchangeable units at scale and do not want to track cost lots, weighted average is the least painful method to automate.
- Use specific identification only for serialized or high-value items. It is overkill for bulk goods.
- Think about tax and reporting. In rising-price environments LIFO lowers taxable income, but it is US-only and adds complexity. If you report under IFRS, LIFO is not an option.
- Stay consistent. Accounting standards expect you to keep the same method period to period. You can change it, but you have to justify and disclose the change, so do not flip methods to flatter a quarter.
Whatever you choose, the method is only as good as the cost data behind it. If your purchase costs, receipts, and quantities are not tracked cleanly per location, no formula will save the valuation.
Where the numbers come from
Valuation runs on clean data: what you paid, when you received it, how much you have, and where it sits. That is a tracking problem before it is an accounting problem. If you run multiple warehouses, you also need per-location stock so the same SKU can carry different quantities without corrupting the average.
Inventoros handles this out of the box. It is free, open source, and self-hosted, so your cost and quantity data stays on infrastructure you control. It tracks multi-location stock and exposes everything through a REST and GraphQL API so you can pull cost layers into your own valuation reports. See the features for the full list, or the documentation to self-host it on cPanel, a VPS, or Docker.
FAQ
Which inventory valuation method is most common? FIFO and weighted average cost are the most widely used. FIFO is popular because it tracks real physical flow and is allowed everywhere. WAC wins on simplicity and is the default in many inventory systems. LIFO is comparatively rare and limited to US GAAP.
Is LIFO allowed under IFRS? No. IFRS prohibits LIFO. Only US GAAP permits it. If you report internationally, or plan to, use FIFO, WAC, or specific identification so you are not forced to restate later.
What is the difference between FIFO and weighted average cost? FIFO expenses your oldest costs first and keeps newer costs in inventory, so results track price movements. WAC blends all costs into a single average and applies it to every unit, which smooths out price swings but hides which specific lot sold.
Can you change inventory valuation methods later? Yes, but not casually. The consistency principle expects you to stick with one method. A change is treated as a change in accounting policy, which usually requires justification, disclosure, and sometimes restating prior periods. Talk to your accountant before switching.