Inventory is what you sell. Supplies are what you use to run your business. That one-sentence distinction drives how each gets recorded in your books, where it appears on your financial statements, and how it affects your taxes.

Inventory includes any products or materials your business holds with the intention of selling to customers. For a retail shop, that’s the merchandise on the shelves. For an e-commerce seller, it’s the products sitting in a warehouse. For a contractor, it might be the lumber and fixtures purchased for a specific project. Inventory sits on your balance sheet as an asset until it’s sold. Once the sale happens, the cost moves to your profit and loss statement as cost of goods sold.

Supplies are the things your business consumes during normal operations. Think office paper, printer ink, cleaning products, packing tape, and trash bags. These items support your work but aren’t part of what you deliver to customers. Supplies get recorded as an expense when purchased and show up on your profit and loss statement right away.

That timing difference is the key financial distinction. If you buy $5,000 worth of product to resell in December but don’t sell it until January, that $5,000 stays on your balance sheet as an asset at year end. It doesn’t reduce your profit for December. But $200 in office supplies bought in December hits your expenses that same month regardless of when you use them.

Where business owners get tripped up is with items that could go either way. Packaging materials are a good example. If the packaging is part of what the customer receives (branded boxes for a subscription product, for instance), it’s typically treated as inventory. If it’s generic shipping materials, it belongs under supplies or shipping expense. The test is whether the item becomes part of the product delivered to the customer.

Another gray area is materials for service businesses. A cleaning company buying cleaning solution isn’t holding inventory. Those chemicals get consumed during service delivery and should be categorized as supplies or as part of cost of goods sold, depending on how you set up your chart of accounts. But if that same company sells cleaning products directly to customers, those products would be tracked as inventory.

Getting this classification wrong distorts your gross profit margin, which is one of the most important numbers for understanding your business. When supplies get mixed into inventory or the other way around, you can’t clearly see what it costs to deliver your product versus what it costs to keep operations running. A small business bookkeeping service will set up your chart of accounts so these categories are clearly separated from the start.

For businesses that carry physical products, proper inventory accounting also means tracking quantities and valuations over time. Supplies don’t need that level of detail. You buy them, expense them, and move on. Inventory requires counts, cost tracking, and adjustments for damaged or obsolete items. The more product you carry, the more this distinction matters for keeping your books accurate and your tax filings correct.

If you’re unsure where a specific expense belongs, ask yourself one question: does this item get sold to a customer or used up by my business? The answer tells you exactly how to categorize it.