Inventory Accounting Methods: FIFO, LIFO, Weighted Average, and Tax Implications

Inventory is the link between what a product-based business spends and what it reports as taxable income. Under IRC 471, businesses that produce, purchase, or sell merchandise must account for inventory to clearly reflect income. The inventory method determines how much of the cost of goods available for sale is allocated to cost of goods sold (reducing taxable income) versus ending inventory (remaining on the balance sheet). During periods of rising prices (which is most of the time), LIFO produces the highest cost of goods sold and the lowest taxable income, while FIFO produces the opposite. The TCJA simplified inventory requirements for small businesses: taxpayers with average annual gross receipts of $32 million or less over the prior 3 years (for 2026) can treat inventory as non-incidental materials and supplies under IRC 471(c), deducting the cost when sold, consumed, or furnished to customers. These small businesses are also exempt from the uniform capitalization (UNICAP) rules under IRC 263A.

How does the inventory method affect your tax bill?

Which inventory costing method should my business use?

The three primary methods are FIFO (First In, First Out), LIFO (Last In, First Out), and weighted average cost. FIFO assumes the oldest inventory is sold first, which produces lower cost of goods sold and higher taxable income during periods of rising prices. LIFO assumes the newest inventory is sold first, which produces higher cost of goods sold and lower taxable income during inflation, but LIFO requires a LIFO conformity rule (you must use LIFO for financial reporting if you use it for tax). Small businesses with average gross receipts of $32 million or less (for 2026) can use the cash method and avoid accounting for inventory under IRC 471, treating inventory costs as materials and supplies deductible when consumed. Changing your inventory method requires filing Form 3115 and computing a Section 481(a) adjustment to prevent double-counting or omitting income during the transition.

Should I use cash basis or accrual basis accounting for my small business?

Cash basis records income when received and expenses when paid, making it simpler and giving you more control over timing. Accrual basis records income when earned and expenses when incurred, regardless of payment timing, providing a more accurate picture of profitability. The IRS requires accrual for businesses with inventory that have average annual gross receipts exceeding $32 million (for tax years beginning in 2026; $31 million for 2025). Below that threshold, you can choose either method. Most small service businesses use cash basis because of its simplicity and the ability to time income and deductions for tax planning. Once you choose a method, switching requires filing Form 3115 and may trigger a Section 481(a) adjustment that spreads the transition impact over four years.

How often should a small business reconcile its accounts?

Monthly reconciliation is the minimum standard for any business, but weekly reconciliation catches errors faster and makes month-end closing significantly easier. Bank reconciliation compares your accounting records to bank statements to identify timing differences (outstanding checks, deposits in transit) and errors (duplicate entries, missed transactions). Credit card reconciliation should happen monthly at minimum, matching each statement charge to a recorded transaction with the correct expense category and ensuring no unauthorized charges slipped through. Businesses with high transaction volume (retail, restaurants, e-commerce) benefit from daily point-of-sale reconciliation, which catches discrepancies before they compound into material misstatements at year-end.

This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.