Your product cost is not just what the supplier charges you. It’s the total amount you spend to get that item into sellable condition. When you source from multiple suppliers with different pricing, shipping methods, and import requirements, getting this number right is the difference between knowing your real margins and guessing at them.

Use the landed cost method for every product. That means your per-unit cost includes four components: the supplier’s unit price, inbound shipping allocated across units in the shipment, import duties and tariffs if the product is coming from overseas, and any prep or labeling fees like FBA prep, poly bagging, or barcode stickering. Add those together and you have your true cost. A product that costs $8.00 on the supplier invoice might actually cost $11.40 once ocean freight, customs duties, and warehouse prep are factored in. If you’re only recording the $8.00, every margin calculation you run is wrong.

When two suppliers sell you the same product at different prices, record each purchase at its actual landed cost. QuickBooks Online tracks COGS on a FIFO basis, meaning when you sell a unit it deducts the cost of the oldest inventory first. If you bought 100 units at $11.40 landed and later 100 more at $12.10 from a different supplier, QBO expenses the $11.40 units first as you sell through them. This works correctly as long as you record each purchase accurately when it happens. Proper inventory accounting requires this discipline with every shipment received.

Set up your inventory items in QuickBooks with enough detail to track costs by product or product category. Don’t lump everything into one generic inventory account. If you sell phone cases and screen protectors, track them separately so you can see COGS for each line. That granularity is what makes your reporting useful.

Run a COGS report by product or category every month. This is how you catch margin erosion before it damages your profitability. Maybe a supplier raised prices 5% three months ago and you never adjusted your selling price. Maybe freight costs from one vendor crept up. Maybe duties changed on a tariff code. You won’t notice any of this looking at total COGS as one number. Breaking it down by category shows you exactly where margins are shrinking and which supplier relationships need attention.

For imported products, keep documentation organized by shipment. Each inbound shipment has its own supplier invoice, freight bill, customs entry, and duty charges. Allocate those costs across the units in that shipment to arrive at your per-unit landed cost. Do this consistently every time product arrives, not retroactively at the end of the quarter when you can’t remember which charges went with which shipment.

The common mistake is treating COGS tracking as something you clean up later. It needs to happen as inventory comes in. If you wait, costs get estimated or averaged incorrectly, and your product-level profitability data becomes unreliable. Every pricing and purchasing decision you make depends on accurate cost data. Our Orange County small business bookkeeping services work with e-commerce sellers to build this tracking into their regular workflow so the numbers are right from the start, not reconstructed after the fact.