These three methods determine how your cost of goods sold gets calculated when you sell inventory that was purchased at different prices over time. A simple example helps. Say you bought 100 units at $5 each in January and another 100 units at $7 each in March. In April, you sell 100 units. The method you use decides which cost hits your income statement.

FIFO (First In, First Out) assumes the oldest inventory sells first. In the example above, your cost of goods sold would be $500 because the $5 units are used first. Your remaining inventory on the balance sheet shows $700. When prices are going up, FIFO produces lower cost of goods sold and higher reported profit. This is the most common method for small businesses, especially retail and food businesses, because it matches the way inventory actually moves. You sell or use older stock before newer stock.

LIFO (Last In, First Out) does the opposite. The most recently purchased units hit cost of goods sold first. So your COGS would be $700 and remaining inventory would sit at $500. Higher COGS means lower profit, which means lower taxes in the short term. That sounds attractive, but LIFO has real drawbacks. It’s not allowed under international accounting standards, it makes your balance sheet inventory values look stale over time, and it adds complexity that most small businesses don’t need. Very few small businesses actually use LIFO.

Weighted average takes all inventory costs and blends them. Total cost of $1,200 divided by 200 units gives you $6 per unit. Sell 100 units and your COGS is $600. This is the simplest method to maintain and works well for businesses with high volumes of similar products where tracking individual purchase lots isn’t practical. Think of a store that buys thousands of similar items at slightly different prices throughout the year.

For restaurants and food businesses, FIFO is almost always the right choice because your inventory is perishable and you’re physically rotating stock. For retail shops and e-commerce sellers, FIFO is also standard because it keeps balance sheet values current and is easy to set up in QuickBooks. Weighted average makes sense for businesses with large quantities of interchangeable products where individual cost tracking would be impractical.

The important thing to understand is that these aren’t just accounting technicalities. The method you choose changes your reported profit, your tax bill, and the value of inventory sitting on your balance sheet. Those differences can add up to real money over the course of a year.

Once you pick a method, the IRS expects you to stick with it. Switching requires approval and can trigger adjustments, so it’s worth choosing correctly from the start. If you carry inventory and aren’t sure which method your books are using or whether it’s set up properly, that’s worth looking into with your bilingual bookkeeping services provider before another year closes with numbers that may not reflect your actual business performance.