How can two identical companies report completely different profits at the end of the year? Imagine they have the exact same products and the same number of sales. It seems impossible, but it's not. The answer comes down to a single accounting choice. It's all about how they value their inventory.
This isn't just a compliance task. It’s a strategic decision. It directly impacts your reported profit, your tax bill, and the story your financials tell. The whole idea is based on a cost flow assumption. And the key word is assumption. It doesn’t have to match how the goods are physically moving off the shelves.
Think about a grocery store. In the dairy aisle, you’re always pushing the older milk to the front. You want it to sell first before it expires. That's FY-foh. First-In, First-Out.
Now, picture the nail bin at a hardware store. Customers just grab a handful from the top. Those are the newest nails that were just dumped in. The old nails from years ago are sitting at the very bottom. That's LIFE-oh. Last-In, First-Out.
To solve an inventory problem, you first need to identify the required method. Is it FY-foh, LIFE-oh, or Weighted-Average? Each method uses the same purchase data, but applies the cost flow assumption differently. A key relationship to remember is that Cost of Goods Sold plus ending inventory must equal the total goods available for sale. This is a useful way to verify your calculation.
Let's walk through the calculations with a hypothetical scenario. Imagine a company uses a periodic system. This just makes the math a bit cleaner for our example.
Let's say they start with a beginning inventory of 100 units at 10 dollars a piece. That's a cost of 1,000 dollars. Then, on April 10th, they buy 200 more units at 12 dollars each. And on April 25th, they buy another 150. Prices went up again, so these were 14 dollars each.
So, all together, they had 450 units available to sell. The total cost was 5,500 dollars. During April, they sold 320 units. This means they have 130 units left in ending inventory.
Okay, let's run the numbers three ways. First up, FY-foh. First-In, First-Out. We need to account for the cost of the 320 units they sold. With FY-foh, we assume we sold the oldest stuff first. So we'll start with the earliest purchases.
We sell all 100 of the beginning units at 10 dollars. That's 1,000 dollars of our COGS. Then we sell all 200 units from the April 10th purchase at 12 dollars. That's another 2,400 dollars. So far, we've accounted for 300 units. We need to get to 320, so we need 20 more. We take those from the next layer, the April 25th purchase, at 14 dollars each. So, 20 times 14 is 280 dollars.
Let's add that up. One thousand dollars, plus 2,400, plus 280. That gives us a total Cost of Goods Sold of 3,680 dollars.
What’s left in ending inventory? We had 150 units in that last purchase, and we only sold 20 of them. So we have 130 units left, all at that 14 dollar cost. That's an ending inventory of 1,820 dollars.
We can confirm our math. The 3,680 dollars in COGS plus the 1,820 in ending inventory equals 5,500 dollars. That correctly matches our total goods available.
Now, let's do the same problem with LIFE-oh. Last-In, First-Out. We sold the same 320 units, but now we assume we sold the newest ones first. We start from the most recent purchases.
We sell all 150 units from the April 25th purchase at 14 dollars. That's 2,100 dollars. We still need to account for 170 more units to get to 320. So, we move to the next newest layer—the April 10th purchase. We sell 170 of those units at 12 dollars each. That's 2,040 dollars.
Our total COGS under LIFE-oh is 2,100 dollars plus 2,040 dollars, which is 4,140 dollars. Notice how it's higher than FY-foh. That's because prices were rising.
So what's left for ending inventory? The oldest stuff. We have the 100 units from beginning inventory at 10 dollars. And we have 30 units left from that April 10th purchase at 12 dollars. That gives us a total ending inventory of 1,360 dollars.
And again, the COGS and ending inventory add up to 5,500. It's important to remember the name: LIFE-oh sells the Last-In units First-Out, so the calculation starts with the most recent purchases.
Finally, there's the weighted-average method. This one smooths everything out. You don't worry about layers. You just calculate one average cost for everything. The total cost of goods available was 5,500 dollars. And we had 450 total units. Divide 5,500 by 450. That gives you an average cost of about 12 dollars and 22 cents per unit.
To get your COGS, just multiply the units sold—320—by that average cost. That gives you a COGS of about 3,911 dollars. For ending inventory, take the remaining 130 units and multiply them by that same average cost. This gives you about 1,589 dollars. And once again, they add up to 5,500.
Let's compare the results in a rising price environment, like our example. With LIFE-oh, you're expensing your newest, most expensive inventory first. This means your COGS is higher. That leads to lower reported income, and a lower tax bill. FY-foh is the exact opposite. And weighted-average will always land you somewhere in the middle.
A key concept with LIFE-oh is LIFE-oh liquidation. This happens when a company sells more inventory than it buys during a period. When that occurs, the company is forced to use older, cheaper inventory layers to calculate its cost of goods sold. The result is an artificially low Cost of Goods Sold. This makes net income appear higher, which increases the company's tax liability. This effect can completely negate the usual tax benefit of using LIFE-oh.
Before we finish, there's one more critical piece. After all this costing, you have to apply a valuation rule. GAAP says you can't overstate your assets. So, inventory has to be reported at the lower of its cost or its net realizable value. We call that NRV.
So what is NRV.? It's the estimated selling price, minus any costs to complete and sell the item. For example, with our FY-foh result, the ending inventory cost was 1,820 dollars. You would compare that cost to the inventory's NRV. If the NRV was lower, you would have to write down the inventory's value. The loss from that write-down would then be reported on the income statement.
The simple Lower of Cost or NRV rule applies to FY-foh and weighted-average. However, for LIFE-oh, the rule is different. It uses a method called Lower of Cost or Market. The "Market" value in this case is more complex. It's determined by three figures. First is the replacement cost. But this cost is bounded by a ceiling and a floor. The ceiling is the NRV. The floor is the NRV minus a normal profit margin. The "Market" value used for the comparison is the middle value of these three numbers: replacement cost, the NRV ceiling, and the NRV-minus-profit floor. This is an important distinction, as the simple NRV rule does not apply to LIFE-oh inventory.
It's helpful to understand how price changes affect the outcomes of these methods. When prices are rising, FY-foh will result in a higher net income compared to LIFE-oh. When prices are falling, the opposite is true. Also, remember that LIFE-oh is prohibited under IFRS. That's a key global distinction.
That covers the essentials of inventory valuation.
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