Manufacturing cost flows describe how every dollar a manufacturer spends on materials, labor, and factory overhead moves through a series of inventory accounts on the balance sheet and eventually lands on the income statement as cost of goods sold. The path is always the same: raw materials inventory, then work in process, then finished goods, then expense at the moment of sale. Getting each transfer right is what lets a manufacturer report accurate margins and know what its products actually cost to make.
The Three Costs That Attach to a Product
Every manufactured unit carries three kinds of cost. They’re called product costs because they ride along with inventory as an asset until the finished item sells.
Direct Materials
Direct materials are the physical inputs you can trace straight to a finished product: steel in a car frame, flour in a loaf of bread, lumber in a cabinet. They sit in raw materials inventory until someone on the floor requisitions them for a specific job. Acquisition cost includes the purchase price plus freight, import duties, and insurance paid to get the materials to the factory.
Direct Labor
Direct labor is the pay for workers whose hands are on the product during conversion — assembly line workers, machinists, welders. The test is whether the worker’s time can be tied to a specific product or production run. Hours logged on time tickets get multiplied by wage rates and flow into work in process.
Manufacturing Overhead
Manufacturing overhead captures every factory cost that isn’t direct materials or direct labor: factory rent, utilities, equipment depreciation, property taxes on the plant, machine lubricants, and the salaries of supervisors who oversee multiple lines. These costs are real and necessary but can’t be economically traced to a single unit.
Because tracing isn’t practical, overhead gets applied to products using a predetermined rate: estimated annual overhead divided by an estimated activity measure such as direct labor hours, machine hours, or direct labor cost. If a company expects $600,000 in overhead and 20,000 machine hours, the rate is $30 per machine hour, and a job that consumes 10 machine hours picks up $300 in applied overhead. Because the rate is built from estimates, applied overhead almost never matches actual overhead, and the gap gets reconciled at year-end.
Product Costs vs. Period Costs
Not every cost a manufacturer incurs flows through inventory. The CEO’s salary, sales commissions, advertising, corporate rent, and the accounting department’s payroll are period costs. They hit the income statement immediately and never touch an inventory account.
The dividing line is where the cost is incurred. A factory supervisor’s salary is overhead and rides with inventory. The sales manager’s salary is a period cost and is expensed right away. Both are salaries; only one has anything to do with making the product. Misclassifying a period cost as a product cost inflates inventory and overstates profit; the reverse pulls expenses forward and understates it.
The Three Inventory Accounts
Manufacturers use three inventory accounts on the balance sheet, and costs move through them in sequence.
Raw Materials Inventory
Raw materials inventory holds everything purchased from suppliers and waiting to enter production. The account rises when materials arrive and falls when they’re issued to the floor. Both direct materials and indirect materials (cleaning solvents, machine lubricants) start here, but indirect materials get routed to manufacturing overhead rather than straight to work in process when they’re pulled.
Work in Process Inventory
Work in process is the central accumulation point. All three product costs converge here: direct materials transferred from raw materials, direct labor recorded from payroll, and manufacturing overhead applied through the predetermined rate. The balance at any point represents the total cost invested in partially completed goods on the factory floor.
Finished Goods Inventory
Finished goods inventory holds the full production cost of completed products waiting to sell. When a customer order ships, those costs leave finished goods and become cost of goods sold on the income statement.
How a Dollar Moves From Purchase to COGS
The cycle runs in one direction: acquire, produce, complete, sell. Each stage triggers a transfer between accounts.
Acquiring Materials
When raw materials arrive, the purchase price plus freight, duties, and insurance gets added to raw materials inventory. The cost is an asset at this point — money spent but not yet consumed.
Entering Production
A materials requisition moves direct materials out of raw materials and into work in process. Indirect materials follow a different path, moving from raw materials into manufacturing overhead. Direct labor enters work in process as workers log time against specific jobs. Manufacturing overhead is applied by multiplying the predetermined rate by the activity measure the company uses. All three streams build up in work in process, job by job or batch by batch.
Completing Production
When goods finish production and clear inspection, their accumulated costs transfer from work in process to finished goods. That transfer amount is called the cost of goods manufactured. Whatever remains in work in process is the cost of units still on the floor.
Selling the Product
When finished goods ship, their cost leaves finished goods and enters cost of goods sold on the income statement. This is the matching principle at work: the cost of producing the goods is recognized in the same period as the revenue from selling them.
Calculating Cost of Goods Manufactured and Cost of Goods Sold
Two calculations summarize the whole flow, and both follow the same pattern: start with what you had, add what came in, subtract what’s still there.
Cost of Goods Manufactured
Cost of goods manufactured (COGM) is the total cost of units that finished production during the period. The calculation runs through work in process:
- Beginning work in process (cost of partially completed goods carried over)
- Plus total manufacturing costs incurred (direct materials used, direct labor, and overhead applied during the period)
- Minus ending work in process (cost of units still incomplete at period-end)
If beginning work in process was $50,000, the company incurred $400,000 in manufacturing costs, and ending work in process is $35,000, COGM is $415,000.
Cost of Goods Sold
Cost of goods sold (COGS) is the cost of the units that actually sold. The calculation runs through finished goods:
- Beginning finished goods inventory
- Plus cost of goods manufactured
- Minus ending finished goods inventory
COGS is the figure that appears on the income statement and gets subtracted from revenue to arrive at gross profit. Everything upstream funnels into this single number.
Cleaning Up Applied vs. Actual Overhead
Because the predetermined rate is built from estimates, the manufacturing overhead account almost always carries a balance at year-end.
If applied overhead was less than actual spending, overhead is under-applied. The account shows a debit balance, meaning some real costs never made it onto products. The standard fix is to increase cost of goods sold by the difference, which zeroes out the overhead account.
If applied overhead exceeded actual spending, overhead is over-applied. The account shows a credit balance, and the adjustment reduces cost of goods sold.
Adjusting cost of goods sold directly is the standard approach and the one most companies use. When the variance is large enough to materially distort financial statements, some companies allocate the adjustment across work in process, finished goods, and cost of goods sold in proportion to their balances. That three-way split is more precise but more complex, and it’s typically reserved for significant discrepancies.
Which Cost Sits in Which Unit
When a manufacturer buys the same material at different prices over time, the accounting has to decide which cost attaches to units sold and which stays in ending inventory. The physical flow of goods doesn’t have to match the cost flow. These are conventions, not warehouse logistics.
- FIFO (first-in, first-out) expenses the oldest costs first. When prices rise, FIFO puts lower historical costs into cost of goods sold and leaves higher recent costs in ending inventory, producing higher reported gross profit.
- LIFO (last-in, first-out) expenses the newest costs first. When prices rise, LIFO pushes higher recent costs into cost of goods sold and lowers taxable income. Any company using LIFO for tax must also use it for financial reporting; that conformity rule is in federal tax law and prevents showing low income to the IRS while showing high income to shareholders.1Office of the Law Revision Counsel. 26 USC 472 – Last-In, First-Out Inventories
- Weighted average blends all unit costs together. It smooths price swings and simplifies calculations but doesn’t provide LIFO’s tax deferral when prices are rising.
All three methods are permitted under U.S. GAAP. Companies reporting under IFRS cannot use LIFO.2FASB. Accounting Standards Update 2015-11, Inventory (Topic 330) The method doesn’t change actual cash spent, but it shifts where profit lands on the financial statements.
Writing Inventory Down When Value Drops
Costs assigned to inventory don’t stay at their original value forever. Under U.S. GAAP, inventory measured using FIFO or weighted average must be carried at the lower of cost or net realizable value, defined as estimated selling price minus costs to complete and sell. If market conditions drop the value below what was paid, the company writes the inventory down and recognizes the loss immediately.2FASB. Accounting Standards Update 2015-11, Inventory (Topic 330)
Inventory measured using LIFO or the retail inventory method follows the traditional lower-of-cost-or-market test, where market is defined as replacement cost subject to a ceiling (net realizable value) and a floor (net realizable value minus normal profit margin). The mechanics differ; the purpose is the same. Inventory on the balance sheet should never overstate what the company can actually recover from it.
Where the IRS Diverges From GAAP
Federal tax rules for inventory don’t always match GAAP. Two provisions matter most.
Uniform Capitalization Under Section 263A
Section 263A of the Internal Revenue Code requires manufacturers to capitalize a broader set of costs into inventory than financial accounting typically demands. Beyond direct materials, direct labor, and factory overhead, the uniform capitalization rules pull in costs like purchasing, storage, and certain administrative expenses that support production. The effect is that more costs get trapped in inventory as assets and fewer get deducted as current expenses.3Office of the Law Revision Counsel. 26 USC 263A – Capitalization and Inclusion in Inventory Costs of Certain Expenses
Small manufacturers are exempt. If average annual gross receipts over the prior three tax years don’t exceed the inflation-adjusted threshold under Section 448(c), Section 263A doesn’t apply. For 2026, that threshold is $32 million.3Office of the Law Revision Counsel. 26 USC 263A – Capitalization and Inclusion in Inventory Costs of Certain Expenses
Simplified Inventory Methods for Small Businesses
The same gross receipts test opens the door to simplified inventory accounting under Section 471. Small businesses that meet it can treat inventory as non-incidental materials and supplies, effectively deducting costs when materials are used or sold rather than tracking them through the traditional three-account system. Alternatively, they can follow whatever inventory method appears in their financial statements.4Office of the Law Revision Counsel. 26 USC 471 – General Rule for Inventories
For a company with $10 million in revenue and straightforward production, the full cost-flow system may be more detail than the IRS requires. Maintaining it internally still makes sense for pricing and operating decisions, even where tax law lets you skip it.