To calculate raw materials inventory used during a period, take beginning raw materials inventory, add net purchases, and subtract ending raw materials inventory. That gives you the dollar value of materials your business actually consumed. If you started the quarter with $200,000 in steel, bought another $350,000, and counted $180,000 still on the shelf at quarter-end, you used $370,000 worth of steel in production.
The math is straightforward. What trips businesses up is getting each input right.
The Three Inputs
Every raw materials calculation rests on three numbers:
- Beginning raw materials inventory. The dollar value of unused materials on hand at the start of the period. This is the same figure as last period’s ending inventory.
- Net purchases. Total cost of materials acquired during the period, including freight and import duties, minus any returns or allowances received from suppliers.
- Ending raw materials inventory. The dollar value of unused materials still in the warehouse at period-end, established by physical count or a perpetual tracking system.
Beginning inventory plus net purchases gives you total materials available for production. Subtract ending inventory from that total and you have raw materials used.
Pulling Each Number
Beginning Inventory
Pull the ending raw materials balance from the prior period’s balance sheet. If your fiscal year ends December 31, the raw materials asset account balance on that date becomes January 1’s beginning figure. It should already reflect any write-downs, shrinkage adjustments, or obsolescence charges from the previous period. If your number doesn’t match the prior period’s audited balance, resolve the discrepancy before doing anything else. Errors here carry forward dollar for dollar.
Net Purchases
Total purchases include the invoice price of every material acquired during the period, plus the transportation and other charges needed to get those goods into your facility. Federal tax regulations require it: the cost of purchased merchandise includes the net invoice price plus “transportation or other necessary charges incurred in acquiring possession of the goods.”1eCFR. 26 CFR 1.471-3 Inventories at Cost Freight-in, customs duties, and insurance during transit all belong in inventory cost, not on a separate expense line.
Then subtract purchase returns and allowances. If a supplier credited you $8,000 for a defective shipment of resin, that $8,000 reduces total materials cost for the period. Miss those adjustments and the raw materials used figure comes out inflated.
Goods in Transit
Materials moving between a supplier and your warehouse raise a timing question at period-end: who owns them? Under FOB shipping point terms, ownership transfers to you the moment goods leave the supplier’s dock, so those materials belong on your books even before they arrive. Under FOB destination terms, the supplier keeps ownership until delivery. Getting this wrong at reporting date means counting inventory you don’t legally own or missing inventory you do. Review shipping terms on open purchase orders near every close.
Ending Inventory
Ending inventory comes from a physical count on the warehouse floor or a perpetual inventory system that tracks every receipt and issue in real time. Most manufacturers do at least one full physical count per year, often supplemented by cycle counting — rotating small subsets of inventory on a schedule so discrepancies surface early. The IRS allows estimated shrinkage rather than a count on the last day of the year, but only if the business normally conducts physical counts at each location on a regular and consistent basis and adjusts its estimates when actual shrinkage differs.2Office of the Law Revision Counsel. 26 USC 471 General Rule for Inventories
Assigning a Dollar Value to Each Unit
Knowing the quantity is only half the calculation. You also need to attach a dollar value to each unit, and the method you pick changes your reported income.
First-In, First-Out (FIFO)
FIFO assumes the oldest materials get used first. When prices are rising, the cheaper early purchases flow into cost of goods sold while more expensive recent purchases stay in ending inventory. Reported profit and tax liability run higher. FIFO also produces a balance sheet value closer to current market prices and mirrors how most manufacturers actually move stock, since older material tends to get pulled first to avoid spoilage or obsolescence.
Last-In, First-Out (LIFO)
LIFO assumes the newest materials are consumed first. In inflationary periods, the highest-cost purchases hit cost of goods sold, lowering taxable income. The tradeoff: balance sheet inventory values can end up sitting at prices from years or decades ago. Businesses that use LIFO for tax purposes must also use it for financial reporting to shareholders and creditors. The IRS enforces this conformity requirement strictly.3eCFR. 26 CFR 1.472-2 Requirements Incident to Adoption and Use of LIFO Inventory Method
Weighted Average Cost
Divide the total cost of all available materials by the total number of units and you get a single average cost per unit. This smooths out price swings and avoids the dramatic profit fluctuations FIFO and LIFO can produce when commodity prices are volatile. For businesses buying the same raw material repeatedly at different prices, weighted average is often the most practical choice.
Specific Identification
When individual units are distinct and trackable, such as custom alloys, gemstones, or specialty lumber, you can assign the actual purchase cost to each specific item. Impractical for high-volume operations, well suited to businesses dealing in expensive, uniquely identifiable materials.
Switching Methods
Once you adopt a valuation method, the IRS expects you to stay with it. Changing methods, such as moving from FIFO to LIFO, requires filing Form 3115, Application for Change in Accounting Method, during the tax year you want the change to take effect.4Internal Revenue Service. 4.11.6 Changes in Accounting Methods The form triggers a Section 481(a) adjustment that prevents income from being duplicated or skipped during the transition. Don’t file it casually. Get professional help if you’re considering a switch.
Writing Inventory Down
Inventory can’t sit on the balance sheet at original cost forever if its value has fallen. Under the lower of cost or market rule, businesses using LIFO compare inventory cost against current replacement cost, capped at net realizable value and floored at net realizable value minus a normal profit margin. Businesses using FIFO or weighted average compare cost directly against net realizable value. When market value drops below what you paid, write inventory down to the lower figure.
Materials that are damaged, obsolete, or otherwise unsalable at normal prices get separate treatment. The IRS requires completely unsalable goods to be removed and excluded from inventory entirely. Subnormal goods that retain some value must be carried at no less than scrap value, and the taxpayer bears the burden of proof, typically by showing an offering for sale, an actual sale, or a contract cancellation within 30 days of the inventory date.5Internal Revenue Service. Lower of Cost or Market (LCM)
What Belongs in Raw Materials and What Doesn’t
Only direct materials go into the raw materials inventory formula. Direct materials become a physical part of the finished product and can be traced to specific units: steel in an auto frame, fabric in a garment, flour in bread. Indirect materials are consumed during production but can’t be economically traced to individual units. Lubricants, cleaning supplies, disposable gloves, and small fasteners bought in bulk go into manufacturing overhead, not raw materials inventory.
Maintenance, repair, and operations supplies follow the same treatment. Spare machine parts, tools, and cleaning chemicals keep the factory running but never become part of what you sell. Dumping them into raw materials inflates the balance sheet and distorts per-unit production costs. If you can’t point to the material inside the finished product, it’s overhead.
Section 263A: Extra Costs You May Have to Capitalize
The formula captures direct material costs, but federal law may require you to load additional indirect costs into inventory value. Section 263A, commonly called the Uniform Capitalization or UNICAP rules, requires manufacturers to capitalize not just direct costs but also an allocable share of indirect production costs, including certain taxes, pension contributions, and portions of management expenses.6Office of the Law Revision Counsel. 26 USC 263A Capitalization and Inclusion in Inventory Costs of Certain Expenses Interest costs get capitalized too, but only for property with a long useful life or a production period longer than two years (or longer than one year if the cost tops $1,000,000).
Small businesses get a real break. If your average annual gross receipts over the prior three tax years fall below the inflation-adjusted threshold under Section 448(c), which was $29 million for 2023 and adjusts upward annually, you can skip UNICAP entirely.2Office of the Law Revision Counsel. 26 USC 471 General Rule for Inventories Qualifying small businesses can even treat inventory as non-incidental materials and supplies or follow the method used in their financial statements. Check the current year’s revenue procedure for the exact threshold.
Mistakes That Distort the Calculation
The arithmetic is simple. The damage happens in the inputs:
- Ignoring freight and duties. Leaving transportation costs out of inventory and expensing them separately understates asset values and misstates the timing of cost of goods sold. Federal regulations require these costs in inventory.1eCFR. 26 CFR 1.471-3 Inventories at Cost
- Forgetting purchase returns. Return $15,000 of defective copper wire but never reduce the purchases figure, and raw materials used comes out $15,000 too high.
- Counting goods you don’t own. Materials shipped FOB destination that haven’t arrived aren’t yours yet. Counting them inflates ending inventory and understates materials used.
- Mixing direct and indirect materials. Dumping lubricants and disposable supplies into raw materials inventory skews per-unit costs and creates classification issues under GAAP.
- Stale ending inventory values. Skipping the lower of cost or market test when commodity prices have dropped leaves the balance sheet overstated.
Raw materials used feeds directly into cost of goods sold, so errors move straight to reported profit and the tax bill. The IRS requires taxpayers producing or selling merchandise to maintain inventories to clearly determine income,2Office of the Law Revision Counsel. 26 USC 471 General Rule for Inventories and accuracy-related penalties for underpayments run as high as 75 percent of the underpaid amount in fraud cases.7Internal Revenue Service. 20.1.5 Return Related Penalties Willful underreporting through falsely inflated cost of goods sold can also cross into criminal tax evasion.8Internal Revenue Service. Tax Crimes Handbook Get the inputs right and the formula takes care of itself.