Inventory affects net income through cost of goods sold: the money you spend on goods sits on the balance sheet as an asset and only reduces reported profit when those goods are sold, written down, lost, or miscounted. Because COGS is subtracted from revenue to get gross profit, anything that pushes more cost onto the income statement in a given period lowers net income for that period, and anything that keeps cost parked as unsold inventory props net income up. The valuation method you choose, the condition of the goods, and the accuracy of your counts all decide how those costs split between the two statements.
How Inventory Turns Into an Expense
While inventory sits in a warehouse, it is a current asset. The cost does not touch the income statement. When a customer buys the item, the cost shifts to cost of goods sold on the income statement. Inventory is a deferred expense in that sense: you already paid for it, but the hit to profit waits for the sale.
The arithmetic is simple. Beginning inventory, plus purchases or production during the period, minus ending inventory, equals cost of goods sold. Higher ending inventory means lower COGS and higher net income for the period. Lower ending inventory means more cost has flowed through, and net income drops. The same pool of costs gets split between the balance sheet and the income statement based on what sold.
Valuation Methods Change the Profit You Report
How you assign costs to the units that sold versus the units still on the shelf can materially change reported profit, even when the physical goods and the sales are identical. The IRS recognizes several methods, and each produces different results depending on which way prices are moving.1Internal Revenue Service. Publication 538, Accounting Periods and Methods
- First-In, First-Out (FIFO) treats the oldest costs as the ones that sold first. When prices are rising, the cheaper older costs flow into COGS and the more expensive recent purchases stay in ending inventory. COGS is lower, net income is higher.
- Last-In, First-Out (LIFO) treats the newest costs as the ones that sold first. During inflation, the more expensive recent costs hit COGS, pushing net income down. The tradeoff is a lower tax bill in the same period.
- Weighted average cost pools all costs and divides by total units for a single per-unit cost. It smooths price swings and lands between FIFO and LIFO.
The gap between methods is not cosmetic. A business with steadily rising input costs can report meaningfully different profit under FIFO than under LIFO with nothing else changing.1Internal Revenue Service. Publication 538, Accounting Periods and Methods
LIFO Comes With a Conformity Rule
If you use LIFO on your tax return, you cannot use a different method to show better numbers to shareholders or lenders. Section 472 of the Internal Revenue Code requires a company using LIFO for tax to use it for all financial reports and credit applications as well. Once you adopt LIFO, you must keep using it every year unless the IRS authorizes a change.2Office of the Law Revision Counsel. 26 USC 472 – Last-in, First-out Inventories The initial choice sticks, and any later switch is treated as a change in accounting method requiring IRS consent through Form 3115.3Internal Revenue Service. About Form 3115, Application for Change in Accounting Method
Write-Downs Reduce Income Before You Sell Anything
Inventory does not always hold its value. Products go obsolete, materials spoil, market prices fall. When inventory value drops below what you paid, accounting rules require you to write it down. Under current U.S. rules, most companies report inventory at the lower of cost or net realizable value. Businesses using LIFO or the retail inventory method still follow the older lower-of-cost-or-market framework.
A write-down is an immediate expense. It reduces net income for the period even though nothing has been sold. If you paid $50,000 for electronics components and the market value falls to $30,000 because a newer technology replaced them, you record a $20,000 loss in the period you recognize the decline. The goods are still in your warehouse; the profit is already gone.
Industries with fast product cycles feel this most: consumer electronics, fashion, anything perishable. Carrying too much stock in these sectors is not just a cash problem. Falling values become reported losses.
Shrinkage Is a Direct Loss
Shrinkage is inventory that vanishes between purchase and count: theft, damage, spoilage, and administrative errors. When a physical count comes in below what your records show, the gap becomes a cost that lowers net income. Small amounts usually get absorbed into COGS. Larger or unusual losses may show as a separate expense line.
The IRS lets businesses use shrinkage estimates during the year rather than waiting for a physical count, but only if they regularly perform physical counts at each location and adjust the estimates against actual results.4Office of the Law Revision Counsel. 26 USC 471 – General Rule for Inventories Physical inventories are required at reasonable intervals, and the books must be adjusted to match the actual count.1Internal Revenue Service. Publication 538, Accounting Periods and Methods
Unlike a write-down, where you still hold reduced-value goods, shrinkage means the inventory is gone entirely. Retailers with high-theft exposure and food businesses with perishable stock generally see the biggest shrinkage effects on their income statements.
Counting Errors Distort Two Separate Years
Miscounts move through the statements in predictable ways. Overcount ending inventory and COGS comes in too low, so net income is inflated. Undercount and the opposite happens: COGS is too high and net income is understated.
These errors are described as self-correcting because this year’s ending inventory becomes next year’s beginning inventory. An overstatement at the end of year one becomes an overstatement at the start of year two, which pushes year-two COGS up and year-two net income down. Across the two years, the totals are right.
The label is misleading, though. Each individual year is still wrong. Inflated first-year income can trigger bonus payouts, mislead investors, and produce incorrect tax payments. By the time the reversal shows up in year two, decisions have already been made on bad numbers. Accurate physical counts are the only reliable safeguard.
UNICAP Pulls Overhead Into Inventory Cost
The cost of inventory is not limited to what your supplier charged. Under Section 263A of the Internal Revenue Code, businesses that produce property or acquire it for resale must capitalize certain indirect costs into their inventory values: warehouse rent, insurance on stored goods, purchasing department salaries, and similar overhead allocable to getting inventory ready for sale.5Office of the Law Revision Counsel. 26 US Code 263A – Capitalization and Inclusion in Inventory Costs of Certain Expenses
These uniform capitalization rules, known as UNICAP, block the immediate deduction of overhead that is really part of producing or holding inventory. Those costs get added to inventory on the balance sheet and only reach the income statement as part of COGS when the goods sell. The effect is deferred expense recognition, which usually increases taxable income in the current year compared to deducting the same costs right away.
UNICAP covers manufacturers and resellers, though the specific costs to capitalize differ between producing goods and buying them for resale.5Office of the Law Revision Counsel. 26 US Code 263A – Capitalization and Inclusion in Inventory Costs of Certain Expenses If the IRS finds that costs which should have been capitalized were deducted instead, correction runs through Form 3115 and can carry additional tax for prior years.6Internal Revenue Service. Instructions for Form 3115
Small Businesses May Be Exempt From Most of This
Not every business carries the full weight of these rules. Section 471(c) creates an exception for small businesses that meet the gross receipts test under Section 448(c), which starts at a base of $25 million in average annual gross receipts and is adjusted for inflation each year.4Office of the Law Revision Counsel. 26 USC 471 – General Rule for Inventories Below that threshold, you can treat inventory as non-incidental materials and supplies (effectively deducting costs when items are used or sold instead of formally tracking inventory), or you can follow whatever method your financial statements already use.
The same gross receipts test exempts qualifying businesses from UNICAP under Section 263A. For a smaller retailer or manufacturer, that removes the overhead allocation work and much of the compliance burden. Because the threshold moves with inflation each year, a growing business that qualifies today may cross the line later and land under the full rules. That crossing is itself a change in accounting method requiring IRS consent.