Theoretically, in a first in, first out system, you’d sell the oldest items in your inventory first. Older products have a tendency to become obsolete over time due to product spoilage, wear and tear, and out-of-date design (if you update the design of the product at any point after your first order). With the FIFO method, you sell those older products first—ensuring that all items in your inventory are as recent as possible.
That being said, FIFO is primarily an accounting method for assigning costs to your goods sold. So you don’t necessarily have to actually sell your oldest products first—you just account for the cost of goods sold using the oldest numbers. In other words, when determining your business’s cost of goods sold (COGS), you would use the costs from the oldest purchase order first, then move on to the costs from the next oldest purchase order and so on.
Because of inflation, businesses using the FIFO method are often able to report higher profit margins than companies using the last in, first out (LIFO) method. That’s because the FIFO method matches older, lower-cost inventory items with higher current-cost revenue. Businesses on the LIFO system, on the other hand, see less of a margin between their current costs and their current revenue.